| 1. |
- Villa, M., et al.
(författare)
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The apparent capacitance of the electrode "charging" process
- 2009
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Ingår i: Physical and Analytical Electrochemistry General Session - 215th ECS Meeting. - San Francisco, CA : The Electrochemical Society. ; , s. 47-59
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We investigate simple models of the electrode charging (discharging) at constant current i, where the potential (E) is recorded as a function of time, or charge, q = i·t. Our goal is to assess the advantages of a representation in terms of capacitance, C = dq / dE ,vs. E. Such a plot is related with cyclic voltammetry (c.v.) plot (ic.v. vs E) at a constant rate (β = dE / dt) since, under appropriate circumstances, we should have C = ic.v. / β = dq / dE. We will discuss the following items: a) origins and suppression of the singularities in the capacitance pilots, b) effects of the finite charging currents, c) comparison between c.v. and electrode charging experiments.
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| 2. |
- Alkadir Abdulahi, Birhan, 1985, et al.
(författare)
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Structural engineering of pyrrolo[3,4-: F] benzotriazole-5,7(2 H,6 H)-dione-based polymers for non-fullerene organic solar cells with an efficiency over 12%
- 2019
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 7:33, s. 19522-19530
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we have synthesized two wide band gap donor polymers based on benzo[1,2-b:4,5-b′]dithiophene (BDT) and pyrrolo[3,4-f]benzotriazole-5,7(2H,6H)-dione (TzBI), namely, PBDT-TzBI and PBDT-F-TzBI and studied their photovoltaic properties by blending them with ITIC as an acceptor. Polymer solar cell devices made from PBDT-TzBI:ITIC and PBDT-F-TzBI:ITIC exhibited power conversion efficiencies (PCEs) of 9.22% and 11.02% and while annealing at 160 °C, improved the device performances to 10.24% and 11.98%, respectively. Upon solvent annealing with diphenyl ether (DPE) (0.5%) and chlorobenzene (CB), the PCE of the PBDT-F-TzBI-based device increased to 12.12%. The introduction of the fluorinated benzodithiophene (BDT-F) moiety on the backbone of PBDT-F-TzBI improved the open circuit voltage, short circuit current and fill factor simultaneously. The high PCEs of the PBDT-F-TzBI:ITIC-based devices were supported by comparison and analysis of the optical and electronic properties, the charge carrier mobilities, exciton dissociation probabilities, and charge recombination behaviors of the devices.
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| 3. |
- Asrat, Daniel, et al.
(författare)
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Prevalence of Helicobacter pylori vacA and cagA genotypes in Ethiopian dyspeptic patients
- 2004
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Ingår i: Journal of Clinical Microbiology. - 1098-660X. ; 42:6, s. 2682-2684
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Tidskriftsartikel (refereegranskat)abstract
- A total of 300 gastric biopsy samples and 50 Helicobacter pylori isolates were collected from Ethiopian adult dyspeptic patients. The vacA and cagA genes were detected in 90 and 79% of biopsy specimens, respectively, and in 100 and 87% of clinical isolates, respectively. Both genes were detected in 84% of the gastric biopsy samples and in 87% of the clinical isolates. Among vacA genotypes, the s1/m1 genotype was the most common in gastric biopsy samples (48%). The vacA and cagA positive H. pylori strains were detected to a higher degree in patients with chronic active gastritis (71%) than patients with other histopathological findings (29%) (P < 0.05).
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| 4. |
- Bjornbom, E., et al.
(författare)
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Reduction of NOx with NH3 in presence of pyrolysed macro-cycle catalyst
- 1991
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Reduction of NOx with NH3 in the presence of pyrolyzed cobalt-tetraphenylporphyrin, CoTPP 'macro-cycle black', was studied. Active carbon, Norit RBXS 1, was used as a carrier. The experimental conditions were varied as follows: temperature from 95 to 140°C, space velocity of the gas mixture 1000-5000 h-1 and catalyst content 0-1%. The results showed that, in the experimental range studied, the temperature has no significant effect on the conversion of NOx. The conversion of NOx at low space velocity of the gas (1000 h-1) was high (approx. 90%), both in the presence and absence of CoTPP black. This was explained by the fact that the active carbon used as a catalyst support also has a catalytic effect on the reduction of NOx. At low space velocity this effect is sufficient to achieve high conversion of NOx in the presence of active carbon only. The conversion decreased at higher space velocity, however. The presence of CoTPP black counteracted the negative effect of the increased space velocity. The effect of the 'macro-cycle black' on the conversion of NOx was significant at higher space velocitites.
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| 5. |
- Burks, Terrance, 1969-
(författare)
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Application of Nanomaterials for the Removal of Hexavalent Chromium and their Biological Implications
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The International Agency for Research on Cancer (IARC) stated that chromium in the form of Cr(VI) has been deemed to be a class-A human carcinogen. It has been a major contaminant associated with wastewater. Moreover, the existence of heavy metals in aquatic systems is a critical concern for the environment as well as industries that manufacture or consume these particular elements. In order to remove these particular toxic metals, several well-known conventional methods including ion-exchange, filtration and adsorption are used. Amongst these methods, adsorption offers significant advantages such as the low-cost materials, ease of operation and efficiency in comparison to the other conventional methods.The aim of this work was to develop nanomaterials (particles and fibers) to address some critical issues for the treatment of heavy metals, especially chromium in aqueous systems. Furthermore, the use of nanomaterials and how they relate to nanoscale operations at the biological level has generated considerable concerns in spite of their novel properties.The first part of this thesis deals with the synthesis and characterizations of Fe3O4, magnetite, as nanoparticles which were further coated with surfactants bis(2,4,4-trimethylpentyl)dithiophosphinic acid, Cyanex-301, and 3-Mercaptopropionic acid with the active compound being the thiol (SH) groups, that will suffice as a viable material for Cr(VI) removal from aqueous solutions. The proposed mechanism was the complexation between the thiol group on Cyanex-301 and 3-Mercaptopropionic acid, respectively. The effect of different parameters on the adsorption including contact time, initial and final Cr(VI) ion concentration and solution pH was investigated.The second part of this thesis encompassed the fabrication of flexible nanocomposite materials, with a large surface area and architecture for the removal of Cr(VI) in batch and continuous flow mode. A technique known as electrospinning was used to produce the nanofibers. The flexible yet functional materials architecture has been achieved by growing ZnO nanorod arrays through chemical bath deposition on synthesized electrospun poly-L-lactide nanofibers. Moreover, polyacrylonitrile nanofibers (PAN) were synthesized and adapted by the addition of hydroxylamine hydrochloride to produce amidoxime polyacrylonitrile nanofibers (A-PAN). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to identify the morphologies and particle sizes whereas Fourier-Transform Infrared spectroscopy (FT-IR) was used to identify either the presence or absence of functional groups for the formation of PAN and A-PAN nanofibers. The optimization of functionalized nanoadsorbents to adsorb Cr(VI) was also carried out to investigate the effect of experimental parameters: contact time, solution pH, initial, final and other metal ion concentration. Commercially manufactured pristine engineered (TiO2, ZnO and SiO2) nanoparticles and lab-made functionalized (Fe3O4 and CeO2) nanoparticles were studied while the powders were suspended in appropriate media by Dynamic Light Scattering (DLS) to identify their cytotoxicity effects.
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| 6. |
- Burks, Terrance, et al.
(författare)
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ZnO-PLLA Nanofiber Nanocomposite for Continuous Flow Mode Purification of Water from Cr(VI)
- 2015
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Ingår i: Journal of Environmental and Public health. - : Hindawi Publishing Corporation. - 1687-9805 .- 1687-9813. ; 2015
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Tidskriftsartikel (refereegranskat)abstract
- Nanomaterials of ZnO-PLLA nanofibers have been used for the adsorption of Cr(VI) as a prime step for the purification of water.The fabrication and application of the flexible ZnO-PLLA nanofiber nanocomposite as functional materials in this well-developedarchitecture have been achieved by growing ZnO nanorod arrays by chemical bath deposition on synthesized electrospun poly-Llactidenanofibers. The nanocomposite material has been tested for the removal and regeneration of Cr(IV) in aqueous solutionunder a “continuous flow mode” by studying the effects of pH, contact time, and desorption steps.Theadsorption of Cr(VI) speciesin solution was greatly dependent upon pH. SEM micrographs confirmed the successful fabrication of the ZnO-PLLA nanofibernanocomposite.Theadsorption and desorption of Cr(VI) species were more likely due to the electrostatic interaction between ZnOand Cr(VI) ions as a function of pH.The adsorption and desorption experiments utilizing the ZnO-PLLAnanofiber nanocompositehave appeared to be an effective nanocomposite in the removal and regeneration of Cr(VI) species.
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| 7. |
- Bursell, Martin, et al.
(författare)
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La0.6Ca0.4CoO3, La0.1Ca0.9MnO3 and LaNiO3 as bifunctional oxygen electrodes
- 2002
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Ingår i: Electrochimica Acta. - 0013-4686 .- 1873-3859. ; 47:10, s. 1651-1660
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Tidskriftsartikel (refereegranskat)abstract
- A series of perovskite catalysts was investigated for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolyte and at room temperature, supplied by oxygen or air. A meniscus cell was used to screen-test candidate catalysts for their bifunctionality and assess their activity for ORR at 3 mm depth of immersion (DOI) in the electrolyte. Based on the meniscus data LaNiO3, La0.1Ca0.9MnO3 and La0.6Ca0.4CoO3 were selected for further assessment in microelectrode and half-cell studies. Activity tests for the ORR and OER, Tafel slopes at high current densities and apparent activation energies for the ORR were determined using a microelectrode technique on samples of the selected perovskites, La0.1Ca0.9MnO3, La0.6Ca0.4CoO3 and LaNiO3 with and without graphite support. Tafel slopes of ca. 120 mV per decade and apparent activation energies of approximately 18 kcal mol(-1) were measured at high cathodic current densities. Cycle-life and performance of La0.1Ca0.9MnO3, La0.6Ca0.4CoO3 and LaNiO3-based gas-diffusion electrodes in half-cell configurations were tested at a constant current density of 25 mA cm(-2) With subsequent and intermittent polarizations. Similar activities resulted in the ORR, while increased numbers of cycles were observed for the La0.1Ca0.9MnO3-based electrode. Furthermore, electrode material compositions, especially PTFE contents were optimized to conform to the establishment of the three phase interactions of the electrode structure, Transmission Electron microscopy (TEM) and BET-surface area analyses were carried out in order to find out the morphological and surface properties of the perovskite materials.
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| 8. |
- Caetano de Souza, Antonio Carlos, et al.
(författare)
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A low cost & safe system of hydrogen production utilizing NaBH4 and CoO catalysis
- 2007
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Ingår i: 2nd International Congress University-Industry Cooperation (UNIDU07).
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Konferensbidrag (refereegranskat)abstract
- The objective of this study was to evaluate the hydrogen production through hydrolysisof sodium borohydride (NaBH4) utilizing catalysts containing CoO. The reactant is safe and stable(when dry) at room temperature. Few works and studies have presented results of investigationsutilizing catalysts containing cobalt; however utilizing catalysts containing CoO were not found yet.In this work simple and cheap hydrogen generation system was developed having reactions atnormal conditions of temperature and pressure. A solution containing a gravimetric composition of10% wt. NaOH, 10% wt. NaBH4 and 80% wt. H2O was utilized. The reaction was carried out atvarious times using the same catalyst to evaluate its performance. This catalyst presented highrates of hydrogen production, especially at its start-up (about 99% of the theoretical hydrogenvolume was produced) at room temperature. After start-up, e.g., when more solution was put, rateof hydrogen production decreased having its production performance also decreased. Probablythis fact occurred due to the formation of the solid phase products such as NaBO2 which might fillthe porous catalyst structure; decreasing the catalytic area. This catalyst is suggested in situationswhere high production rates are necessary such as start-up of fuel cells.
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| 9. |
- Caetano de Souza, Antonio Carlos, et al.
(författare)
-
Hydrogen production through hydrolysis of NaBH4: The use of catalysts containing Pt and Pt-Ru
- 2007
-
Ingår i: 2nd International Congress University-Industry Cooperation (UNIDU07).
-
Konferensbidrag (refereegranskat)abstract
- Several works about hydrolysis of NaBH4 utilizing various catalysts (such as catalysts containing Pt or Ru) are available in the literature. Investigations involving NaBH4 has increased due to the possibility to produce hydrogen using simple and safe systems, even at room temperatures with very high efficiencies. A solution containing a gravimetric composition of 10%wt. NaOH, 10%wt. NaBH4 and 80%wt. H2O was utilized and the reaction was initiated immediately as soon as this solution was put in the chosen catalysts, in this case, catalysts containing Pt and mixtures of Pt-Ru. Catalysts containing Pt and Pt-Ru presented high yields of hydrogen after the solution being inserted in the reaction vessel several times. In this study it was found out that the rates of hydrogen production were increased with catalysts containing Pt and Pt-Ru (99 and 96% of theoretical hydrogen production respectively). The catalysts containing Pt presented higher production rate, while the catalysts containing the mixed Pt-Ru presented a quasi-linear production, e.g., stable production rate.
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| 10. |
- Chamoun, Mylad, et al.
(författare)
-
Bifunctional Performance of Flow Assisted Rechargeable Iron-Air Alkaline Batteries
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Low cost rechargeable iron-air alkaline batteries have all essential attributes to adapt for large scale energy storage applications. To actualize this implementation needs to overcome the challenges including poor efficiency and short cycle lifetime. Herein, suitable synthesized catalysts for the air electrode were investigated prior to iron-air cell testing. NiCo2O4 as sole catalyst proved exceptional bifunctional OER/ORR activity and stability over 440 h operation in air. This catalyst fitted into an electrolyte and oxygen flow assisted rechargeable iron-air prototype and performed stable over 588 h and had an energy density of 377 Wh kg-1 Fe. Inadequate coulombic efficiencies of 75 – 85% and energy efficiencies around 50% hurt the performance of the cell though and needed further development. Nevertheless, the findings in this work reports the opportunities and obstacles of the rechargeable iron-air battery.
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| 11. |
- Chamoun, Mylad, et al.
(författare)
-
Electrochemical Performance and in Operando Charge Efficiency Measurements of Cu/Sn-Doped Nano Iron Electrodes
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Fe-air or Ni-Fe cells can offer low-cost and large-scale sustainable energy storage. At present, they are limited by low coulombic efficiency, low active material use, and poor rate capability. To overcome these challenges, two types of nanostructured doped iron materials were investigated: (1) copper and tin doped iron (CuSn); and (2) tin doped iron (Sn). Single-wall carbon nanotube (SWCNT) was added to the electrode and LiOH to the electrolyte. In the 2 wt. % Cu + 2 wt. % Sn sample, the addition of SWCNT increased the discharge capacity from 430 to 475 mAh g−1, and charge efficiency increased from 83% to 93.5%. With the addition of both SWCNT and LiOH, the charge efficiency and discharge capacity improved to 91% and 603 mAh g−1, respectively. Meanwhile, the 4 wt. % Sn substituted sample performance is not on par with the 2 wt. % Cu + 2 wt. % Sn sample. The dopant elements (Cu and Sn) and additives (SWCNT and LiOH) have a major impact on the electrode performance. To understand the relation between hydrogen evolution and charge current density, we have used in operando charging measurements combined with mass spectrometry to quantify the evolved hydrogen. The electrodes that were subjected to prolonged overcharge upon hydrogen evolution failed rapidly. This insight could help in the development of better charging schemes for the iron electrodes.
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| 12. |
- Dong, Hanwu, et al.
(författare)
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An air-metal hydride battery using MmNi(3.6)Mn(0.4)Al(0.3)Co(0.7) in the anode and a perovskite in the cathode
- 2010
-
Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 35:9, s. 4336-4341
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen storage alloy MmNi(3.6)Mn(0.4)Al(0.3)Co(0.7) (MH) was tested as anode material in a metal hydride-air cell. The cathode was a non-noble metal air electrode based on a mixture of perovskite and pyrolyzed macrocycles on carbon. Polarization and discharge capacities of the electrodes were measured and compared at 22 degrees C and 40 degrees C using air or oxygen at the cathode. Discharge capacity reaching 330 mAh/g MH with pure oxygen at 40 degrees C and 305 mAh/g MH with air at 22 degrees C were obtained. Power densities and/or energy densities were found to significantly depend on the increase of the electrode kinetics on both the ORR (oxygen reduction reaction) and HOR (hydrogen oxidation reaction). However, for air electrode, an increase of oxygen concentration by using pure oxygen gas plays a more important role than an 18 degrees C temperature increase. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
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| 13. |
- Endalew, Abebe K., et al.
(författare)
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Heterogeneous catalysis for biodiesel production from Jatropha curcas oil (JCO)
- 2011
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 36:5, s. 2693-2700
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Tidskriftsartikel (refereegranskat)abstract
- This work focuses on the development of heterogeneous catalysts for biodiesel production from high free fatty acid (FFA) containing Jatropha curcas oil (KO). Solid base and acid catalysts were prepared and tested for transesterification in a batch reactor under mild reaction conditions. Mixtures of solid base and acid catalysts were also tested for single-step simultaneous esterification and transesterification. More soap formation was found to be the main problem for calcium oxide (CaO) and lithium doped calcium oxide (Li-CaO) catalysts during the reaction of jatropha oil and methanol than for the rapeseed oil (RSO). CaO with Li doping showed increased conversion to biodiesel than bare CaO as a catalyst. La(2)O(3)/ZnO, La(2)O(3)/Al(2)O(3) and La(0.1)Ca(0.9)MnO(3) catalysts were also tested and among them La(2)O(3)-ZnO showed higher activity. Mixture of solid base catalysts (CaO and Li-CaO)and solid acid catalyst (Fe(2)(SO(4))(3)) were found to give complete conversion to biodiesel in a single-step simultaneous esterification and transesterification process. (C) 2011 Elsevier Ltd. All rights reserved.
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| 14. |
- Endalew, Abebe K., et al.
(författare)
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Inorganic heterogeneous catalysts for biodiesel production from vegetable oils
- 2011
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Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 0961-9534 .- 1873-2909. ; 35:9, s. 3787-3809
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Forskningsöversikt (refereegranskat)abstract
- Biofuels are renewable solutions to replace the ever dwindling energy reserves and environmentally pollutant fossil liquid fuels when they are produced from low cost sustainable feedstocks. Biodiesel is mainly produced from vegetable oils or animal fats by the method of transesterification reaction using catalysts. Homogeneous catalysts are conventionally used for biodiesel production. Unfortunately, homogeneous catalysts are associated with problems which might increase the cost of production due to separation steps and emission of waste water. Inorganic heterogeneous catalysts are potentially low cost and can solve many of the problems encountered in homogeneous catalysts. Many solid acid and base inorganic catalysts have been studied for the transesterification of various vegetables oils. The work of many researchers on the development of active, tolerant to water and free fatty acids (FFA), as well as stable inorganic catalysts for biodiesel production from vegetable oils are reviewed and discussed.
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| 15. |
- Eriksson, Tore, et al.
(författare)
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Temperature swing adsorption device for oxygen-enriched air
- 2014
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Ingår i: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526 .- 1879-1786. ; 76, s. 174-179
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Tidskriftsartikel (refereegranskat)abstract
- In connection with a project aimed at producing oxygen-enriched air from ambient air using temperature differences in the so-called temperature swing adsorption (TSA), a device was designed and constructed that took into consideration most of the conceivable parameters governing such a process. While designing the device, care was taken so that it was adaptable to different operating modes, fulfilling high versatility and extending to more processes than producing oxygen-enriched air. The device was small-scale, mounted on a movable table. It was equipped with a total of 54 individually controllable on/off valves. The valves could be controlled at a resolution of 1 s using a programmable logic controller, controlled by a personal computer, so the time program for the valves could be easily exchanged for a readymade program. The device had six cylinders, with removable lids filled with zeolite and easily maintained plastic tubing, which could therefore be changed or replaced without much difficulty. The results show that 15 L of oxygen could be produced at a concentration of 30% in the oxygen-enriched air per kg zeolite and hour. Equipping the device in the future with valves that close and open securely in both directions would vastly extend the possibility of using this technology to other applications, in addition to this method of TSA process for air separation.
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| 16. |
- Fatima, Masoom, et al.
(författare)
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Low-Cost Single Chamber MFC Integrated With Novel Lignin-Based Carbon Fiber Felt Bioanode for Treatment of Recalcitrant Azo Dye
- 2021
-
Ingår i: Frontiers in Energy Research. - : Frontiers Media SA. - 2296-598X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- A flow through anaerobic microbial fuel cell (MFC) was designed and optimized for efficient treatment of recalcitrant textile wastewater. The membrane-less MFC was first time fabricated with a unique combination of electrodes, a novel bioanode of synthesized lignin-based electrospun carbon fiber supporting a biofilm of Geobacter sulfurreducens for acetate oxidation and an air-breathing cathode, consisting of a pyrolyzed macrocycle catalyst mixture on carbon bonded by polytetrafluoroethylene (PTFE). The effects of different organic loadings of acetate along with Acid Orange (AO5), operation time and ionic strength of auxiliary salts (conductivity enhancers) were investigated and responses in terms of polarization and degradation were studied. In addition, the decomposition of the organic species and the degradation of AO5 along with its metabolites and degraded products (2-aminobenzenesulfonic acid) were determined by chemical oxygen demand (COD) analysis, UV-Vis spectrophotometry and high-performance liquid chromatography (UV-HPLC) techniques. SEM and TEM images were also used to find out the biocompatibility of the microbes on lignin-based electrospun carbon felt anode and the morphology of the cathode. Reduction and breakage of the azo bond of AO5 occurs presumably as a side reaction, resulting in the formation of 2-aminobenzenesulfonic acid and unidentified aromatic amines. Maximum current density of anode 0.59 Am-2 and power density of 0.12 Wm(-2) were obtained under optimized conditions. As a result, decolouration of AO5 and chemical oxygen demand (COD) removal efficiency was 81 and 58%, respectively. These results revealed that the low-cost MFC assembly can offer significant potential for anaerobic decolouration of recalcitrant textile wastewater.
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| 17. |
- Gebru, Bahre, et al.
(författare)
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The role of forest status in households’ fuel choice in Uganda
- 2023
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Ingår i: Energy Policy. - : Elsevier. - 0301-4215 .- 1873-6777. ; 173
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate how households' choice of energy source is influenced by the status of the local forest resource. We assume that households choose between clean fuels (e.g., kerosene, LPG, solar, and electricity), dirty biobased fuels (e.g., firewood, animal dung, crop residues, and charcoal), and mixed fuels. We integrate socioeconomic data with high-resolution satellite data on forest conditions from the Uganda National Panel Survey. The findings from a random-effects multinomial logit model indicate that households in vegetated areas are 6–7% less likely to rely solely on dirty biobased fuels, and 6–8% more likely to use mixed fuels, compared to those in non-vegetated areas. A larger forest stock is more strongly associated with lower use of firewood than charcoal. A possible explanation for the findings is the presence of policies for forest conservation and enhanced forest property rights, which improve forest conditions and limit opportunities to collect firewood. Given households' dependence on forest-based fuels, such policies could need to be modified to secure households’ access to these fuels.
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| 18. |
- Han, Ruiping, et al.
(författare)
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Review on Heat-Utilization Processes and Heat-Exchange Equipment in Biogas Engineering
- 2016
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Ingår i: Journal of Renewable and Sustainable Energy. - : AIP Publishing. - 1941-7012. ; 8:3
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Tidskriftsartikel (refereegranskat)abstract
- With the increasing demand for environmental protection and renewable energy, bioenergy technology has been attracting considerable attention. Anaerobic digestion (AD) is the process to convert the low-grade biomass into bioenergy, in which both heat-recovery and -recycling should be treated carefully in order to improve the process efficiency. In this work, the heat-recovery and its utilization processes were reviewed, and different types of heat exchangers as well as their advantages in biogas engineering were surveyed. It shows that the recovery and utilization of the waste heat from biogas plants with an internal system, such as slurry effluent unit, the combined heat and power unit, the sanitation unit, and the internal recycle unit, are important for improving the AD efficiency of biogas production. For example, the recovery and recycling of waste heat from the effluent can result in a 2-3 °C temperature increase for the inlet manure slurry. For thermophilic AD, the heat recovery from effluent can save about 50% of the total heat requirement. The external heating process is more suitable for large- and medium-scale biogas plants, and the heat transfer coefficient of external heating (850-1000 W/m2 K-1) is almost two-times higher than that of the internal heating (300-400 W/m2 K-1). To utilize the waste heat in biogas plants, heat exchangers have been designed for biogas slurry. However, further improvement on the heat exchangers with anti-blockage, anti-fouling, high efficiency, and low investment is still needed. Moreover, the heat exchanger suitable for a low-temperature-difference system is specially needed in China, but the development is still in its infancy. Therefore, to tailor to the Chinese national conditions, special external heating processes should be designed and reoriented to the diversity of biomass, the climatic environmental conditions, and the renewable Chinese policies
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| 19. |
- Hu, W. K., et al.
(författare)
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AB(5)-type hydrogen storage alloys as catalysts in hydrogen-diffusion electrodes for novel H-2/hydride//perovskite/O-2 alkaline fuel cells
- 2004
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:48, s. 18530-18534
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Tidskriftsartikel (refereegranskat)abstract
- Development of a non-noble-metal catalyst electrode is an important issue in the research and development of fuel cells. The catalytic activity and durability of AB(5)-type hydrogen storage alloys used in hydrogen-diffusion electrodes for alkaline fuel cells are evaluated. The experiments demonstrate that the activity and stability for hydrogen oxidation is greatly improved if the particle size is decreased from 5-30 to 1-10 mum. This also improves the electrode stability. SEM and XRD analyses show that no disintegration of the smaller catalyst particles is observed in long-term tests. A novel H-2/hydride//perovskite/O-2 alkaline fuel cell was constructed as a non-noble-metal fuel cell concept. The results showed that both gas-diffusion electrodes had high catalytic activities and good stability. A maximum power density of 54 mW/cm(2) was achieved at 120 mA/cm(2) when using H-2/O-2 and 49 mW/cm(2) at 100 mA/cm(2) when using H-2/air.
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| 20. |
- Hu, W. K., et al.
(författare)
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Zr-based AB(2)-type hydrogen storage alloys as dual catalysts of gas-diffusion electrodes in an alkaline fuel cell
- 2004
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:26, s. 8756-8758
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Tidskriftsartikel (refereegranskat)abstract
- Zr-based AB(2)-type hydrogen storage alloys as dual catalysts for hydrogen adsorption and oxidation reactions in alkaline fuel cells were investigated. A hydrogen-diffusion electrode composed of this hydride alloy was constructed, and its performance in terms of catalytic activities and durability was evaluated. Results demonstrated that the hydrogen-diffusion electrode had not only good activity but also excellent stability at a current density of 40-60 mA/cm(2) after surface treatments using a 1.0 M HF solution. XPS analyses showed that the improvement in catalytic activity is related to the formation of a nickel-rich layer and the removal of other oxides on the catalyst surface. The novel possible application of Zr-based hydride alloys could lead to an attempt to exploit new catalysts to lower material cost for hydrogen fuel cells.
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| 21. |
- Jukka-Pekka, Spets, et al.
(författare)
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Test of Different Anode Electrocatalysts for Direct Glucose Anion Exchange Membrane Fuel Cell
- 2016
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Ingår i: International Journal of Electrochemical Science. - : Electrochemical Science Group. - 1452-3981. ; 11:6, s. 4219-4230
-
Tidskriftsartikel (refereegranskat)abstract
- Direct glucose anion exchange membrane fuel cell (AEMFC) with near-neutral-state electrolyte of 0.1 M [PO4] (tot) was studied with five different anode electrocatalysts (Pt, PtRu, PtNi, Au, PdAu) at a temperature of 37 degrees C and at a glucose concentration of 0.1 M. The cathode catalyst in each test was Pt supported on carbon (60 wt.%). Four anode electrocatalysts (supported on carbon) had a total metal content of 40 wt.% while the fifth anode material of PtRu had a higher content of 60 wt.%. Moreover, in order to show the influence of the metallic content on the fuel cell performance, anode catalysts with 60 wt.% (Pt) and 10wt.% (PtNi) were tested. The operation of the AEMFC was controlled by means of an in-house-made electronic load with PI-controller (i.e. a feedback controller that has proportional and integral action on control error signal) either at constant current (CC) or at constant voltage (CV). The primary objective was to characterize the Coulombic efficiency (CE) based on the exchange of two electrons and compare the specific energy (Wh kg(-1)) for the direct glucose AEMFC related to the different electrode combinations and electrocatalysts. As a result of these screening tests, two most efficient anode electrodes with Pt and PtNi were selected to be used for further AEMFC studies.
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| 22. |
- Jukka-Pekka, Spets, et al.
(författare)
-
Towards an Efficient Direct Glucose Anion Exchange Membrane Fuel Cell System with Several Electro-Oxidation Units
- 2017
-
Ingår i: International Journal of Electrochemical Science. - : ESG. - 1452-3981. ; 12:5, s. 3697-3708
-
Tidskriftsartikel (refereegranskat)abstract
- This work covers the direct glucose anion exchange membrane fuel cell (AEMFC) with near-neutralstate electrolyte of 0.1 M [PO4] (tot) having two high-performing anode electrocatalysts (Pt and PtNi) at 37 degrees C and at a glucose concentration of 0.1 M. The cathode catalyst in each test was a Pt supported on carbon (60 wt.%). The PtNi/C had a total metal content of 40 wt.% and the Pt/C 60 wt.%. The operation of the AEMFC was controlled by means of an in-house made electronic load with PI-controller (i.e. a feedback controller, which has proportional and integral action on control error signal). There were two primary objectives with this study. At first, to find out how the electrode modifications of the anode (i.e. by increasing the thicknesses of these electrodes by adding extra carbon) affect the Coulombic efficiency (CE, based on the exchange of two electrons) and the specific energy (SPE, Wh kg(-1)) values of the direct glucose AEMFC. Secondly, investigate how a two-stage fuel cell system with two fuel cells concatenated and used one after the other for the electrochemical oxidation of glucose, influence the CE and SPE values. The results show that the modified PtNi anode shows superior results for the AEMFC compared to our earlier results. As for the two-stage fuel cell system, it increased the average electric power (mWh) and SPE when compared to single fuel cell systems except when the higher selective anode catalyst (Pt) was used in the first fuel cell prior to the fuel cell in the second fuel cell containing the lower selective anode catalyst (PtNi).
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| 23. |
- Kiros, Bahre
(författare)
-
Essays on the impact on households of natural resource scarcity and climate change
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis comprises four empirical papers aimed at comprehending the interdependencies among climate change, scarcity of natural resources such as water and forests, human health, and households’ responses.Paper I investigates the impact of precipitation variability on households’ sanitation technology choices in Ethiopia. The findings indicate that increased precipitation variability causes households to abandon improved sanitation facilities in favor of unimproved sanitation systems. Paper II examines how local forest resource conditions affect households’ fuel choice in Uganda. The use of biobased fuels has detrimental effects on both human health and forests. The results show that, when compared to households in non-vegetated areas, those in more vegetated areas are less likely to depend on dirty biobased fuels like firewood and charcoal. A larger forest stock is associated with a greater likelihood of using a combination of clean and dirty fuels. Paper III analyzes the impacts of water scarcity, as measured by time spent collecting water, on diarrhea prevalence and the purchase of health insurance in Ethiopia. Results show that water scarcity has a significant and positive impact on both. Finally, paper IV scrutinizes the effects of seasonal temperature on seasonal farm labor market outcomes in Ethiopia. The main findings show that rising temperatures reduce the number of hired farm labor days and wage payments during planting, harvesting, and whole agricultural season.
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| 24. |
- Kiros, Yohannes, 1956-, et al.
(författare)
-
Cobalt and cobalt-based macrocycle blacks as oxygen-reduction catalysts in alkaline fuel cells
- 1993
-
Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 45:2, s. 219-227
-
Tidskriftsartikel (refereegranskat)abstract
- The electrochemical reduction of oxygen on high surface are carbons catalyzed by cobalt and pyrolyzed macrocycles has been studied in alkaline fuel cells. Tests were also carried out with 'green black', i.e., pyrolyzed phyto-biomass. Galvanostatic polarization curves show that cobalt from cobalt acetate and fine cobalt metal power exhibit a high catalytic activity. The activity of pyrolyzed cobalt tetraphenylporphyrin (CoTPP) is due to the combined effects of the cobalt additive and the charred residue of the macrocycle. 'Green black', with chlorophyll as macrocycle black precursor, has a similar effect. The dissolution of cobalt from the electrode surface has been established. Life tests with these electrodes are reported. © 1993.
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| 25. |
- Kiros, Yohannes, et al.
(författare)
-
Cost-effective perovskite for intermediate temperature solid oxide fuel cells (ITSOFC)
- 2001
-
Ingår i: Journal of New Materials for Electrochemical Systems. - 1480-2422. ; 4:4, s. 253-258
-
Tidskriftsartikel (refereegranskat)abstract
- Low lanthanum containing perovskite, Ca0.9La0.1MnO3 (CLM) was synthesized. The material was characterized and examined as a cathode for the intermediate temperature (400 to 650C) solid oxide fuel cell (ITSOFC) applications. ITSOFCs using this cost-effective perovskite as a cathode displayed an excellent cell performance: between 300 and 1500 mA/cm(-2) (100 to 500 mWcm(-2)) for temperatures ranging from 450 to 600 degreesC. The role of AgO as additive to the perovskite has also showed an enhancement in the fuel cell performance.
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| 26. |
- Kiros, Yohannes, et al.
(författare)
-
Determination of the thicknesses of the active layer and cathode limiting currents in AFC
- 2004
-
Ingår i: Electrochemistry communications. - : Elsevier BV. - 1388-2481 .- 1873-1902. ; 6:6, s. 526-530
-
Tidskriftsartikel (refereegranskat)abstract
- A series of double-layered gas diffusion electrodes with two different electrocatalysts, i.e., Ag and pyrolyzed macrocycle mixture (PMM) were prepared in order to find out the maximum limiting current densities (i(L)) by varying the oxygen partial pressures in 6 M KOH and at 65 degreesC. As optimization of the active (catalyst) layer is important for better utilization of the catalytic reactions for oxygen reduction and thereby attainment of high current density, electrochemical measurements in half-cells were carried out to substantiate the current-thickness relationships. The thicknesses for both the active layers and diffusion layers were determined by using SEM. i(L) for an oxygen concentration simulating that of air was found to be 2.2 A cm(-2) for the PMM with 0.51 mm and 1.6 A cm-2 for the Ag-based catalyst with 0.56 mm thicknesses of the active layer. An overlay of a mathematical model, describing the parameters for determination of i(L), has also been inserted alongside the experimental values.
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| 27. |
- Kiros, Yohannes, et al.
(författare)
-
Effect and characterization of dopants to Raney nickel for hydrogen oxidation
- 2003
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 360:02-jan, s. 279-285
-
Tidskriftsartikel (refereegranskat)abstract
- Raney nickel and its alloys with the transition metals were prepared and investigated as gas diffusion electrodes for the hydrogen oxidation reaction (HOR) in 6 M KOH and at 60degreesC. The spongy Raney nickel prepared by a mixture of Ni and Al with a weight ratio of 1: 1 was compared for the catalytic activity as hydrogen electrodes with other alloy formations containing 2 wt.% of Cu, Fe, Cr, Ti and La. Depending on the composition of the active layer, the electrocatalytic activity of the Raney nickel was found to decrease in a descending order of the doped metals: Cr>La>Ti>Cu>Fe and with no admixture. The catalytic response of the electrodes, especially for the Cr and Ti-based Raney Ni showed high enrichment and aggregation on the surface and hence affects the activity and stability. Surface area, particle size. average pore diameter, particle morphology and surface elements of the various alloy combinations, have been analyzed and assessed using BET-specific surface areas, SEM and EDXS.
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| 28. |
- Kiros, Yohannes, 1956-
(författare)
-
Electrocatalytic properties of Co, Pt, and Pt-Co on carbon for the reduction of oxygen in alkaline fuel cells
- 1996
-
Ingår i: Journal of the Electrochemical Society. - : Electrochemical Society. - 0013-4651 .- 1945-7111. ; 143:7, s. 2152-2157
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of cobalt, platinum, and cobalt-platinum, alloys on high surface area carbons for oxygen reduction in alkaline electrolyte was investigated. The Pt-Co catalyst with ca. 1:3 atomic ratio was prepared by addition of H2PtCl6 solution to a mixture of methanol and a 5% surfactant in deionized water containing cobalt acetate and carbon suspension. This was followed by drying and heat-treatment at 700 and 900°C in a flow of hydrogen and nitrogen gas mixtures. Polarization curves and kinetic parameters for Pt, Co, and Pt-Co were conducted and compared in 6 M KOH and at 80°C. Higher activities were observed for the Pt-Co alloy, that had been heat treated at 900°C. In addition to increased activity of this catalyst, the unalloyed base metal (Co) contributes to total performance improvement of the oxygen reduction process. Furthermore, surface, structural, and chemical characterizations of the catalysts were carried out using transmission electron microscopy, x-ray diffraction, Brunauer, Emmett, and Teller method, and atomic absorption spectroscopy. Dissolution of cobalt from the electrodes, both from the single cobalt phase and Pt-Co alloy catalysts, has been established. The x-ray results demonstrated a shift to lower lattice parameters (3.618 Å) by the Pt-Co alloys, prepared at 900°C, than the pure platinum catalyst (3.919 Å).
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| 29. |
- Kiros, Yohannes, 1956-, et al.
(författare)
-
Electrode R&D, stack design and performance of biomass-based alkaline fuel cell module
- 1999
-
Ingår i: International journal of hydrogen energy. - : Pergamon Press. - 0360-3199 .- 1879-3487. ; 24, s. 549-564
-
Tidskriftsartikel (refereegranskat)abstract
- Electrode formulations with di}erent materials and manufacturing techniques were tested electrochemically in order to assess their stability and activity in long!term operations. Cathode electrocatalysts such as CoTPP, Ca0.9La0.1MnO3 and Pt-Co alloys were incorporated in high surface area carbons and operated at a constant load of 100 mA cm-2 80C and an electrolyte concentration of 6M KOH. Similarly, anode catalysts with Pt-Pd bimetallic combinations were also tested and ascertained in half!cell measurements. Surface area measurements and Transmission Electron Microscopy (TEM) analyses were carried out both before and after the electrochemical test procedures. The electrodes were incorporated into a seven and two cell module design of the external and internal manifolding types and the experiences gained from these design principles are described, respectively. Furthermore, a biomass fed AFC module with all the system descriptions, steps, and a demonstration layout of producer gas to alkaline fuel cell are examined and discussed. Wood charcoal and agro-residues were used as feedstock and as a primary fuel. Power output of the different feedstock in a producer gas fed alkaline fuel cell has the shown potentiality and effciency to be applied as a stand alone power generator.
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| 30. |
- Kiros, Yohannes, 1956-, et al.
(författare)
-
Gas diffusion electrode
- 2012
-
Patent (populärvet., debatt m.m.)abstract
- A method of preparing a gas diffusion electrode comprising a diffusion layer, and a reaction layer arranged to eachother, wherein the diffusion layer is prepared by i) admixing a) sacrificial material, b) polymer and c) a metal - based material and d)optional further components, wherein the sacrificial material has a release temperature below about 275 °C and is added in anamount from about 1 to about 25 wt% based on the total weight of components a) -d) admixed; ii) forming a diffusion layer from theadmixture of step i); iii) heating the forming diffusion layer to a temperature lower than about 275 °C so as to release at least a partof said sacrificial material from the diffusion layer. A gas diffusion electrode comprising a diffusion layer and a reaction layer ar -ranged to one another, wherein the diffusion layer has a porosity ranging from about 60 to about 95 %, and an electrolytic cell comprising the electrode. An electrolytic cell, a fuel cell comprising the gas diffusion electrode and a metal-air battery comprising thegas diffusion electrode.
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| 31. |
- Kiros, Yohannes, et al.
(författare)
-
Long-term hydrogen oxidation catalysts in alkaline fuel cells
- 2000
-
Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 87:02-jan, s. 101-105
-
Tidskriftsartikel (refereegranskat)abstract
- Pt/Pd bimetallic combination and Raney Ni catalysts were employed in long-term electrochemical assessment of the hydrogen oxidation reaction (HOR) in 6 M KOH. Steady-state current vs. potential measurements of the gas diffusion electrodes have shown high activity for these types of catalysts. Durability tests of the electrodes have shown increased stability for the Pt/Pd-based catalysts than the Raney Ni at a constant load of 100 mA/cm(2) and at temperatures of 55 degrees C and 60 degrees C, respectively. Surface, structural and chemical analyses by BET surface area, transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) were used to characterize the composite electrode/catalyst both before and after the electrochemical testing.
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| 32. |
- Kiros, Yohannes, et al.
(författare)
-
Low energy consumption in chlor-alkali cells using oxygen reduction electrodes
- 2008
-
Ingår i: International Journal of Electrochemical Science. - 1452-3981. ; 3:4, s. 444-451
-
Tidskriftsartikel (refereegranskat)abstract
- An air/oxygen gas diffusion electrode for use as a cathode to replace the traditional hydrogen-evolving electrode in chlor-alkali electrolysis was assessed. Attempts to stabilize the cathode have been addressed in order to circumscribe problems associated with "flooding" or "wetting-in" properties. Variation of the hydrophobic concentration in the gas diffusion layer had a significant effect on the electrochemical tests of both the half-cell and electrolysis of the chlor-alkali cells. Life-tests as well as performance characteristics for both types of cells have shown encouraging results at NaOH concentration levels of ca 8M NaOH and temperatures of 70 and ca. 80 degrees C, respectively. Though cell voltages of about 2V were achieved and thereby reducing the energy consumption by 30-35% compared to the state-of-the-art membrane cell, the contributions of overvoltages were still high compared to the equilibrium potential of about 1.23V. Efforts to limit the individual parts of overvoltages as well as maintenance of the zero-gap cell at least on the anode side have been carried out. Two different kinds of cation exchange membranes have been used for the electrolysis cell. However, the cation exchange membrane with hydrophilic properties having high initial performances showed tendencies of blister formations.
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| 33. |
- Kiros, Yohannes
(författare)
-
Metal porphyrins for oxygen reduction in PEMFC
- 2007
-
Ingår i: International Journal of Electrochemical Science. - 1452-3981. ; 2:4, s. 285-300
-
Tidskriftsartikel (refereegranskat)abstract
- A short literature review on alternative catalysts for the cathodic oxygen reduction in acid (H2SO4) and polymer electrolyte membrane fuel cell ( PEMFC) with special emphasis on pyrolyzed macrocycles and precursor materials from metals, organic molecules and N-containing elements has been conducted. Furthermore, various catalytic materials comprising two different concentrations of iron and cobalt tetramethoxyphenyl porphyrins and perovskites were prepared by both the impregnation and precipitation reactions. Screening tests of the individual catalytic materials and their mixtures were carried out in half-cell measurements using the rotating disc electrode (RDE) in 0.5M H2SO4 and at room temperature. Cyclic voltammograms were recorded at a scan rate of 10 mV s(-1) both with and without rotations. The peak potential at 0 rpm was used to study and compare the catalytic activities towards oxygen reduction reaction (ORR). Concentrations of 30wt% Fe and Co/TMPP have shown increased performance characteristics, while those with lower or increased contents, acid-treated and mixed with perovskite have displayed lower activities. Polarization data for the catalyst containing 30wt% FeTMPP was also obtained. Acid leaching of the pyrolysis products has resulted in substantial decrease of the metals from the pyrolysis products supported on carbon. TEM, BET-surface area and EDX analyses on the samples have shown high aggregation of the metals with crystalline structure, surface areas depending on the compositions of the catalysts and increased surface concentration of the metals with absence of nitrogen on the moiety.
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| 34. |
- Kiros, Yohannes, 1956-
(författare)
-
Oxygen reduction electrode
- 2002
-
Patent (populärvet., debatt m.m.)abstract
- The invention refers to an oxygen reduction electrode comprising at least three layers: a current collector, a diffusion layer comprising at least PTFE; and a catalytical active layer comprising at least a mixture of perovskites and pyrolysed macrocycles. In this way, oxygen may be utilised from air without an initial removal of carbon dioxide. Moreover, the invention refers to methods for preparing the electrode, as well as fuel cells and other products wherein the electrode can be used.
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| 35. |
- Kiros, Yohannes, et al.
(författare)
-
Oxygen reduction electrodes for electrolysis in chlor-alkali cells
- 2006
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 51:16, s. 3346-3350
-
Tidskriftsartikel (refereegranskat)abstract
- Oxygen reduction electrodes, containing non-noble metal catalysts supported on high surface area carbon and wet-proofed with PTFE were tested under reaction conditions for the chlor-alkali electrolysis. Double-layer gas diffusion electrodes were prepared by rolling of an active layer and diffusion layer on a nickel wire screen, compressed and sintered at 300 degrees C. Electrochemical measurements for substantiating the activity and stability of the half-cells were conducted in 8 M NaOH by supplying oxygen at a cell temperature of 70 degrees C and a constant current load of 300 mA cm(-2). An electrolysis cell with a dimensionally stable anode (DSA) and double-layered cathode was assembled, where 4.8 M NaCl and oxygen were supplied, respectively, for the production of chlorine and NaOH. The cell performances as well as stability of the electrodes were investigated at about 80 degrees C. This study shows that by replacing the high voltage consuming hydrogen-evolving reaction and by adopting highly active electrocatalysts as cathode materials, energy savings of more than 30% could be realized.
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| 36. |
- Kiros, Yohannes, et al.
(författare)
-
Preparation of high surface area La0.1Ca0.9MnO3 and its electrochemical activities
- 2007
-
Ingår i: THERMEC 2006, Pts 1-5. - 9780878494286 ; , s. 1361-1366
-
Konferensbidrag (refereegranskat)abstract
- The use of perovskites as potential heterogeneous catalysts in a number of chemical and electrochemical reactions have attracted the research interest due to high surface reactivity and low cost. Since catalysis is strongly dependent on surface areas, texture and structural homogeneity, the development of effective modes of preparation of perovskites is of utmost importance for the achievement of high performances, especially for electrochemical applications in fuel cells and metal/air batteries. The precipitation reaction method for the synthesis of La0.1Ca0.9MnO3 at low temperatures in the presence of alkaline support electrolyte has shown significant gain in the surface and electrochemical properties. Enhanced BET-surface area of this production method as compared to the dry pyrolysis method was obtained. Multifunctional application for cathodic reactions in alkaline fuel cell (AFC) and intermediate temperature solid oxide fuel cell (IT-SOFC) as well as for bifunctional systems of both oxygen reduction reaction (orr) and oxygen evolution reaction (oer) has been investigated. Parameter optimisations of the ingoing materials and analyses of the solid-state properties of the catalyst pertaining to structural, chemical and surface characteristics have also been carried out.
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| 37. |
- Kiros, Yohannes, 1956-, et al.
(författare)
-
Pyrolyzed macrocycles on high surface area carbons for the reduction of oxygen in alkaline fuel cells
- 1991
-
Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 36:4, s. 547-555
-
Tidskriftsartikel (refereegranskat)abstract
- Polarization characteristics and preparation methods of double-layer porous gas diffusion electrodes on various carbon materials in alkaline fuel cells were investigated. The electrodes with active carbon carriers were catalyzed with cobalt/iron tetraphonylporphyrin or silver. These electrodes show a potential of - 186 mV (versus Hg/HgO) at 1.0 A/cm2 when operated with oxygen at 40 °C and 5 M KOH. Various techniques such as surface area measurements, scanning (SEM) and transmission (TEM) electron microscopy in combination with energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS) were used to characterize the structure and morphology of the catalyst layer.
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| 38. |
- Kiros, Y.
(författare)
-
Separation and permeability of zincate ions through membranes
- 1996
-
Ingår i: Journal of Power Sources. - 0378-7753. ; 62:1, s. 117-119
-
Tidskriftsartikel (refereegranskat)abstract
- A novel method for the separation of zincate ions in alkaline media has been developed. This development uses a precipitation reaction of Mn(OH)2 and application on a microporous separator (Celgarde). The amount of zinc, passed through the membranes was estimated by electrogravimetric method. Different inorganic materials in combination with the separator material have been tested. Effective low grade permeability of zincate ions and increased resistivities have been found to be related to the amount of Mn(OH)2 applied on the separator.
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| 39. |
- Lampinen, Markku J., et al.
(författare)
-
Research on bioorganic fuels as power sources
- 2010
-
Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 35:22, s. 12635-12641
-
Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the kind of the bioorganic fuel cells that are equipped with or without ion exchange membranes The bioorganic materials of interest are alcohols (methanol ethanol) and glucose which are obtained from renewable energy sources such as biomass The operation temperatures of the direct fuel cells cover from room temperature up to 150 C The direct bioorganic fuel cells belong to the subject area of Advanced fuel cells of the Working group 4 in the EU COST Action 543 among the collaborating Universities and Institutes Bioorganic fuel cells are suitable for application in small portable power sources such as backups battery chargers and in electronic devices A number of current and earlier works are summansed and advances are highlighted in this area with special emphasis on glucose as a fuel.
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| 40. |
- Li, Zhuofeng, 1991-, et al.
(författare)
-
Tuning morphology, composition and oxygen reduction reaction (ORR) catalytic performance of manganese oxide particles fabricated by γ-radiation induced synthesis
- 2021
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 583, s. 71-79
-
Tidskriftsartikel (refereegranskat)abstract
- A γ-radiation induced synthesis method is used to fabricate manganese oxide catalysts through both reduction and oxidation routes. It is shown that the morphology, composition and electrochemical performance of the produced manganese oxide particles can be tuned by altering the redox conditions. The catalysts prepared via radiolytic oxidation have a hollow spherical morphology, possess γ-MnO2 structure and show high catalytic activity for the complete four-electron reaction pathway of the oxygen reduction reaction (ORR) in alkaline electrolyte. Meanwhile, the catalysts synthesized via radiolytic reduction possess a rod-like morphology with a Mn3O4 bulk structure and favour the incomplete two-electron reaction pathway for ORR. The high catalytic activity of the manganese oxide synthesized via the oxidation route can be attributed to high electrochemical surface area and increased amount of Mn3+ on the surface as compared to those in the sample obtained via the reduction route.
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| 41. |
- Marini, S., et al.
(författare)
-
Advanced alkaline water electrolysis
- 2012
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 82, s. 384-391
-
Tidskriftsartikel (refereegranskat)abstract
- A short review on the fundamental and technological issues relevant to water electrolysis in alkaline and proton exchange membrane (PEM) devices is given. Due to price and limited availability of the platinum group metal (PGM) catalysts they currently employ, PEM electrolyzers have scant possibilities of being employed in large-scale hydrogen production. The importance and recent advancements in the development of catalysts without PGMs are poised to benefit more the field of alkaline electrolysis rather than that of PEM devices. This paper presents our original data which demonstrate that an advanced alkaline electrolyzer with performances rivaling those of PEM electrolyzers can be made without PGM and with catalysts of high stability and durability. Studies on the advantages/limitations of electrolyzers with different architectures do show how a judicious application of pressure differentials in a recirculating electrolyte scheme helps reduce mass transport limitations, increasing efficiency and power density.
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| 42. |
- Marini, S., et al.
(författare)
-
Oxygen evolution in alkali with gas diffusion electrodes
- 2013
-
Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 38:26, s. 11496-11506
-
Tidskriftsartikel (refereegranskat)abstract
- Progresses in the area of the oxygen evolution reaction (OER) are now occurring at a much faster rate relative to few years ago. For this reason, it has been deemed appropriate to present a critical review of the major and most recent contributions towards a fundamental understanding of what determines the OER electrocatalytic properties of a material. Furthermore, the technologies used to produce practical OER electrodes with top activities are assessed and the current benchmarks of performance are identified. Furthermore, results pertaining to our work on Raney-Ni gas diffusion anodes, which have been optimized in thickness and composition, are presented. An addition of 10 wt.% of a Co3O4 micrometric powder as co-catalyst (with Raney Ni-Fe) was found to enhance the polarization behavior and performance. The electrode so obtained achieves activities comparable with those of the best electrodes reported in the literature. Great emphasis has been placed in the analysis of the stability of the prepared Gas Diffusion Electrodes. Most of the GDEs were found to be stable in weeks long experiments with intermittent operation. The issue of integrating several functional layers (gas diffusion layer, active layer with current collector, separator layer) within a single, mechanically strong electrode assembly is briefly addressed.
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| 43. |
- Marini, S., et al.
(författare)
-
Stable and inexpensive electrodes for the hydrogen evolution reaction
- 2013
-
Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 38:26, s. 11484-11495
-
Tidskriftsartikel (refereegranskat)abstract
- The HER activities of Raney-Ni electrodes obtained by partial leaching of Al in a Ni-Al-Fe alloy doped with Mo, Cr or Pd were studied in 28% KOH. PTFE bonded Gas Diffusion Electrodes (GDEs) were prepared by the rolling method before sintering at 300 degrees C under N-2. Ni in alkaline electrolyte has a lower intrinsic HER activity than Pt in acid. However, the spongy and highly porous character of Raney-Ni greatly enhances HER resulting in a cheap material with outstanding catalytic performance. The polarization behavior of GDEs consisting mainly of Raney-Ni catalysts with optional addition of co-catalyst or conductivity enhancing powders, such as carbonyl iron, carbonyl nickel, copper and molybdenum oxide are studied as a function of temperature and time in order to determine activities, behavior in the high current density regime, and long term stability in view of potential exploitation in industrial electrolysis. Cr and Pd-doped Raney-Ni initially achieve outstanding performances with unusually low "Tafel slopes". After weeks long cathodic treatments, these GDEs eventually attain inferior but stable activities due to an apparently irreversible aging of Raney-Ni. The aging of Mo-doped Raney-Ni is less conspicuous, and relevant performances are sometimes improved by additives. A clear picture is emerging of the mechanisms controlling polarization and aging behavior of Raney-Ni GDEs. From this picture, suggestions are put forward on how to improve stability and performances of full electrode assemblies and make them suitable for use in advanced alkaline electrolyzers.
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| 44. |
- Meheretu, Yonas, et al.
(författare)
-
Prevalence of orthohantavirus-reactive antibodies in humans and peri-domestic rodents in northern Ethiopia
- 2021
-
Ingår i: Viruses. - : MDPI. - 1999-4915. ; 13:6
-
Tidskriftsartikel (refereegranskat)abstract
- In 2012, Tigray orthohantavirus was discovered in Ethiopia, but its seasonal infection in small mammals, and whether it poses a risk to humans was unknown. The occurrence of small mammals, rodents and shrews, in human inhabitations in northern Ethiopia is affected by season and presence of stone bunds. We sampled small mammals in two seasons from low-and high-density stone bund fields adjacent to houses and community-protected semi-natural habitats in Atsbi and Hagere Selam, where Tigray orthohantavirus was first discovered. We collected blood samples from both small mammals and residents using filter paper. The presence of orthohantavirus-reactive antibodies in blood was then analyzed using immunofluorescence assay (human samples) and enzyme linked immunosorbent assays (small mammal samples) with Puumala orthohantavirus as antigen. Viral RNA was detected by RT-PCR using small mammal blood samples. Total orthohantavirus prevalence (antibodies or virus RNA) in the small mammals was 3.37%. The positive animals were three Stenocephalemys albipes rats (prevalence in this species = 13.04%). The low prevalence made it impossible to determine whether season and stone bunds were associated with orthohantavirus prevalence in the small mammals. In humans, we report the first detection of orthohantavirus-reactive IgG antibodies in Ethiopia (seroprevalence = 5.26%). S. albipes lives in close proximity to humans, likely increasing the risk of zoonotic transmission.
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| 45. |
- Menya, E., et al.
(författare)
-
Characterization and alkaline pretreatment of rice husk varieties in Uganda for potential utilization as precursors in the production of activated carbon and other value-added products
- 2018
-
Ingår i: Waste Management. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0956-053X .- 1879-2456. ; 81, s. 104-116
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Tidskriftsartikel (refereegranskat)abstract
- In this study, 13 rice husk (RH) varieties from 4 agro-ecological zones in Uganda were characterized, NaOH-pretreated, and evaluated for their potential utilization as precursors for production of bio-oil, ash, char, and activated carbon for selected applications. RH varieties were characterized through particle size analysis, bulk density, proximate and ultimate analyses, specific surface area, pore volume, as well as lignocellulosic and inorganic compositions. Selected RH varieties were subsequently pretreated at NaOH concentrations of 1-4%w/v, using pretreatment ratios of 5 g RH: 40 mL NaOH. Properties varied among RH varieties, suiting them as feedstocks for different applications. Upland rice husk varieties are more suited precursors for production of bio-oil, and activated carbon due to their relatively lower ash content, higher specific surface area, as well as higher volatile matter and fixed carbon contents. Upland rice husks could as well be employed in the preparation of electrodes for electrochemical devices, due to their relatively higher specific surface area. A high ash content (21-32% dry basis) of lowland rice husks presents good prospects for their calcination, since larger amounts of rice husk ash could be obtained, and employed in different applications. Lowland rice husk varieties could also be more suited precursors for production of char for soil amendment, due to their relatively higher ash content, which subsequently increases their char yields. However, alkaline pretreatment of rice husks using 2-4%w/v NaOH can reduce the ash content by as much as 74-93%, depending on the rice husk variety, which paves way for utilizing rice husks with a high ash content in different applications. Aside from ash reduction, the enhanced specific surface area (1.2-1.7 m(2) g(-1)), volatile matter (68-79%db) and fixed carbon (19-24%db) contents of NaOH-pretreated rice husks suggests they are more suited feedstocks than when employed in their raw form, for production of bio-oil, as well as activated carbon.
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| 46. |
- Menya, E., et al.
(författare)
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Effect of alkaline pretreatment on the thermal behavior and chemical properties of rice husk varieties in relation to activated carbon production
- 2020
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Ingår i: Journal of thermal analysis and calorimetry (Print). - : Springer Science and Business Media LLC. - 1388-6150 .- 1588-2926. ; 139:3, s. 1681-1691
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Tidskriftsartikel (refereegranskat)abstract
- Thermal behavior and chemical properties of selected raw and NaOH-pretreated rice husk varieties were investigated. NaOH-pretreatment process involved soaking 5 g rice husk samples in 40 mL of 2%w/v NaOH, shaking (400 rpm) and heating (50 °C) for 3 h. NaOH-pretreated samples were water-washed, oven-dried, and milled for use in the determination of their thermal behavior and surface functional groups. Alkaline wash-water was also analyzed for sugar components. Thermal decomposition temperatures, degradation rates, and the subsequent mass losses varied from one rice husk variety to another. These thermal properties increased after NaOH-pretreatment of the rice husk varieties, reducing their char yields (17.1–20.4% db). These changes mainly had to do with the lignin, hemicellulose, and ash removal from the rice husk varieties, as confirmed by their FTIR analysis, as well as by the sugar composition analysis of their alkaline wash-water. Consequently, the FTIR spectra differed between the raw and NaOH-pretreated rice husk varieties.
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| 47. |
- Menya, E, et al.
(författare)
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Optimization of pyrolysis conditions for char production from rice husks and its characterization as a precursor for production of activated carbon
- 2020
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Ingår i: Biomass Conversion and Biorefinery. - : Springer. - 2190-6815 .- 2190-6823. ; 10, s. 57-72
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Tidskriftsartikel (refereegranskat)abstract
- Response surface methodology was employed to optimize pyrolysis conditions for production of char with maximumyield, fixedcarbon content, and with minimum ash content from Uganda’s New Rice for Africa (NERICA) 1 rice husk variety. The aim wasto obtain rice husk char with more suitable properties as an activated carbon precursor. Mathematical models were developed toexplain the relationships between the experimental responses and the pyrolysis parameters of temperature (400–600 °C), heating rate (10–25 °C min−1), and heating period (60–120 min). The optimized rice husk char was further characterized for elementaland proximate compositions, thermal behavior, specific surface area, as well as surface functional groups. Results from theanalysis of variance (ANOVA) revealed that the quadratic model best fits each of the responses. Pyrolysis temperature had thegreatest influence on each of the responses, followed by heating period, and lastly heating rate. Optimum pyrolysis conditionswere found to be temperature (406 °C), heating rate (10 °C min−1), and heating period (60 min), resulting in char yield, fixedcarbon, and ash contents of 35.26, 55.39, and 35.01% dry basis, respectively. Compared to raw rice husk, the resulting rice huskchar was found more suited as activated carbon precursor, due to its enriched carbon content (60.35%) and specific surface area (123.9 m2 g−1). Thermogravimetric analysis of the rice husk char revealed that thermal activation temperatures higher than 400 °C may be required to considerably devolatilize the char, forming a more porous activated carbon.
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| 48. |
- Menya, E., et al.
(författare)
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Production and performance of activated carbon from rice husks for removal of natural organic matter from water : A review
- 2018
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Ingår i: Chemical engineering research & design. - : Institution of Chemical Engineers. - 0263-8762 .- 1744-3563. ; 129, s. 271-296
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Forskningsöversikt (refereegranskat)abstract
- Adsorption by activated carbon has great potential to improve natural organic matter (NOM) removal from water. However, the high production and regeneration costs limit its wide scale application. To address these limitations, research efforts have been focused on finding low cost materials that can be transformed into activated carbon. Rice husk is one of such materials of research focus, especially in the developing countries, where over 96% of rice husks are generated globally. Although numerous investigations have been made concerning the production of activated carbon from rice husks, the existing scientific information still remains widely scattered in literature. Furthermore, the scientific information regarding performance of rice husk activated carbon during NOM removal from water still remains poorly documented. This review article therefore provides ample information on efforts made by various researchers concerning production of activated carbon from rice husks and its adsorption performance in relation to NOM removal from water. Properties and pretreatment of rice husks in relation to production of activated carbon are discussed. Activation of rice husks by physical and chemical methods under numerous conditions is reviewed. Factors affecting NOM adsorption by activated carbon are briefly discussed. Adsorption performance of rice husk activated carbon is also reviewed with respect to NOM removal from water, and where possible compared with other source derived activated carbons. The data from literature revealed that NOM removal by rice husk activated carbon can be as effective as commercial activated carbon. Consequently, rice husk activated carbon has potential to serve as an alternative to commercial activated carbon.
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| 49. |
- Menya, E., et al.
(författare)
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Synthesis and evaluation of activated carbon from rice husks for removal of humic acid from water
- 2022
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Ingår i: Biomass Conversion and Biorefinery. - : Springer Nature. - 2190-6815 .- 2190-6823. ; 12:8, s. 3229-3248
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Tidskriftsartikel (refereegranskat)abstract
- Activated carbon was synthesized from the New Rice for Africa (NERICA) rice husk variety, followed by its evaluation for removal of humic acid from water. Product values of carbon yield, C and total specific surface area, as,BET were employed as the performance criterion. The best physically activated carbon resulted from char activation at 800 °C for 10 min, leading to as,BET and C×as,BET values of 756.8 and 402.7 m2 g−1, respectively. The best chemically activated carbon resulted from 30 wt% H3PO4 activation of rice husk at 400 °C for 30 min, leading to as,BET and C×as,BET values of 2258.4 and 1058.7 m2 g−1, respectively. Despite the higher as,BET value, the maximum adsorption capacity of the best chemically activated carbon (5.3 mg g−1) was found lower than 8.9 and 27.2 mg g−1 exhibited by the chemically activated carbons prepared at 500 and 600 °C, respectively. The best adsorption conditions included carbon dose of 0.5 g, solution pH of 2, and contact time of 60 min. The adsorption capacity of the prepared activated carbons (27.2 mg g−1) was comparable to that of the commercial activated carbon (30.40 mg g−1). The analyses of the adsorption isotherms and kinetics revealed that the experimental data fits well the Langmuir isotherm model, as well as the pseudo-second-order kinetic model. The latter suggests that the adsorption of humic acid onto the activated carbon was controlled by the chemisorption process. Overall, the study revealed that the NERICA rice husk variety has good prospects for preparation of activated carbons for humic acid adsorption.
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| 50. |
- Nissinen, T. A., et al.
(författare)
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MnCo2O4 preparation by microwave-assisted route synthesis (MARS) and the effect of carbon admixture
- 2003
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 15:26, s. 4974-4979
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Tidskriftsartikel (refereegranskat)abstract
- Catalyst spinel MnCo2O4 with particle size <30 nm was prepared by a novel microwave-assisted route. To determine the optimal amount of carbon needed as a microwave susceptor, varying amounts of amorphous carbon powder (7-26 wt %) were mixed with the aqueous solutions of Mn- and Co-nitrates. After heat treatment at 200degreesC in a conventional oven, the mixtures were heat-treated in a microwave oven (2.45 GHz) at a power of 350 W. The effect of the carbon amount on the formation and properties of the catalysts was studied. In this production method, 13 wt % of carbon was found to be the minimum needed for spinel MnCo2O4 formation. Most of the carbon was oxidized during the microwave treatment. When the carbon content in the nitrate-carbon mixture was increased beyond 13 wt %, the carbon content and the specific surface area of the final catalyst started to decrease. However, the carbon amount of 18 wt % in the initial nitrate-carbon mixture was found to be the most preferable when considering the catalytic activity of the spinel toward oxygen reduction reaction in alkaline electrolyte.
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