| 1. |
- Lindberg, Aleksandra, 1990-
(författare)
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Selectivity and gas composition in electrochemical systems by mass spectrometry
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This doctoral thesis presents experimental studies of gaseous products of two electrochemical systems: the chlorate process and the nickel-metal hydride (NiMH) battery, employing mass spectrometry.The cathodic efficiency for the hydrogen evolution reaction (HER) of the chlorate process was investigated by employing ex-situ synthesized MnOx electrodes. Without the addition of toxic chromium (VI), used today in industry, high cathodic efficiency was achieved. The effect of different annealing temperatures in the electrode preparation on HER efficiency was examined. The addition of 1000 times lower concentrations of chromium (VI) than used in the industry today, together with in-situ added molybdate,showed promising results in keeping high cathodic efficiency and selectivity towards HER. The evolution of oxygen decreases anodic efficiency and also presents a safety risk due to simultaneously proceeding of HER in the undivided cell. The amount of produced oxygen by two types of electrodes TiRu and TiRuSnSb, was followed. Oxygen is produced by homogenous hypochlorite decomposition, heterogeneously by different electrode surface present in the electrolyte solution and anodically during the electrolysis i.e. electrochemically.Investigating gas composition in batteries presents a challenge due to the complexity of reactions leading to the gas evolution.Additionally, the gas consumption has a significant impact on the amount and constituents of the collected gases. The methodology for investigating gas composition of the NiMH battery without influencing the battery performance was established. Two technologies, sampler and microcapillary, gave reasonable and complementing results.
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| 2. |
- Abbasi, M., et al.
(författare)
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Fabrication of Spin-Coated Ti/TiHx/Ni-Sb-SnO2 Electrode : Stability and Electrocatalytic Activity
- 2018
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Ingår i: Journal of the Electrochemical Society. - : ELECTROCHEMICAL SOC INC. - 0013-4651 .- 1945-7111. ; 165:9, s. H568-H574
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Tidskriftsartikel (refereegranskat)abstract
- A novel three-layer anode having the composition Ti/TiHx/Ni-Sb-SnO2 (Ti/TiHx/NATO) was successfully prepared by a spin-coating and pyrolysis process aiming at a long service lifetime and good electrocatalytic properties for ozone formation. The TiHx as an interlayer was produced by electrochemical cathodic reduction of a coated layer of the TiOx on the titanium substrate. Spin coating and thermal decomposition were used to deposit the Sn-Sb-Ni precursor on the surface of the prepared Ti/TiHx electrode. Cyclic and linear scanning voltammetry, Raman spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to reveal the electrode performance and morphology. Results show that the onset potential for the oxygen evolution reaction (OER) of Ti/TiHx /NATO is higher than for Ti/NATO. They also indicate that the service lifetime of the Ti/TiHx/NATO is twice as long as the Ti/NATO at a current density of 50 mA.cm(-2) at room temperature. Electrochemical ozone generation and degradation of the methylene blue were investigated to confirm selectivity and activity of the electrodes. After 5 min electrolysis, a current efficiency for ozone generation of 56% was obtained the electrode with TiHx while 38% was obtained on Ti/NATO under same conditions. The results also confirm that the Ti/TiH x /NATO has a higher kinetic rate constant and decolorization efficiency for removal of the methylene blue compare to the Ti/NATO. The rate constant for the pseudo-first ordered reaction of methylene blue degradation showed high values of 350 x 10(-3) min(-1) for Ti/NATO and 440 x 10(-3) min(-1) for Ti/TiHx/NATO.
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| 3. |
- B. Araujo, Rafael, et al.
(författare)
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Elucidating the role of Ni to enhance the methanol oxidation reaction on Pd electrocatalysts
- 2020
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 360
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Tidskriftsartikel (refereegranskat)abstract
- Amongst promising available technologies enabling the transition to renewable energy sources, electrochemical oxidation of alcohols, in a direct fuel cell or in an electrolysis reaction (H-2 production), can be an economically and sustainable alternative to currently used technologies. In this work, we highlight the advantages of a Pd-Ni bimetallic electrocatalyst for methanol electrooxidation - a convenient choice due to the low cost of Ni combined with the observed acceptable catalytic performance of Pd. We report a synergistic effort between experiments and theoretical calculations based on density functional theory to provide an in-depth understanding - at the atomistic level - of the origin of the enhanced electrochemical activity of methanol electrooxidation using the bimetallic catalysts Pd3Ni and PdNi over pure Pd. Cyclic voltammograms and High-Performance Liquid Chromatography (HPLC) demonstrate higher activity towards methanol electrooxidation with increased Ni concentration and, furthermore, higher selectivity for CO2. These effects are understood by: 1) changes in the methanol oxidation reaction mechanism. 2) Mitigation or suppression of CO poisoning on the Pd-Ni alloys as compared to the pure Pd catalyst. 3) A stronger tendency towards highly oxidized intermediates for the alloys. These findings elucidate the effects of a bimetallic electrocatalyst for alcohol electrooxidation as well as unambiguously suggest PdNi as a more cost-effective alternative electrocatalyst.
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| 4. |
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| 5. |
- White, Jai, et al.
(författare)
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Synergistic Bimetallic PdNi Nanoparticles : Enhancing Glycerol Electrooxidation while Preserving C3 Product Selectivity
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Electrochemical conversion of glycerol offers a promising route to synthesise value-added glycerol oxidation products (GOPs) from an abundant biomass-based resource. While noble metals provide a low overpotential for the glycerol electrooxidation reaction (GEOR) and high selectivity towards three-carbon (C3) GOPs, their efficiency and cost can be improved by incorporating non-noble metals. Here, we introduce an effective strategy to enhance the performance of Pd nanoparticles for the GEOR by alloying them with Ni. The resulting PdNi nanoparticles show a significant increase in both specific activity (by almost 60%) and mass activity (by almost 25%) during the GEOR at 40 °C. Additionally, they exhibit higher resistance to deactivation compared to pure Pd. Analysis of the GOPs reveals that the addition of Ni into Pd does not compromise the selectivity, with glycerate remaining at around 60% of the product fraction, and the other major product being lactate at around 30%. Density functional theory calculations confirm the reaction pathways and the basis for the higher activity of PdNi. This study demonstrates a significant increase in the GEOR catalytic performance, while maintaining the selectivity for C3 GOPs, using a more cost-effective nanocatalyst.
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| 6. |
- Yu, Xiaowen, et al.
(författare)
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Electrocatalytic Glycerol Oxidation with Concurrent Hydrogen Evolution Utilizing an Efficient MoOx/Pt Catalyst
- 2021
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Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 17:44
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Tidskriftsartikel (refereegranskat)abstract
- Glycerol electrolysis affords a green and energetically favorable route for the production of value-added chemicals at the anode and H2 production in parallel at the cathode. Here, a facile method for trapping Pt nanoparticles at oxygen vacancies of molybdenum oxide (MoOx) nanosheets, yielding a high-performance MoOx/Pt composite electrocatalyst for both the glycerol oxidation reaction (GOR) and the hydrogen evolution reaction (HER) in alkaline electrolytes, is reported. Combined electrochemical experiments and theoretical calculations reveal the important role of MoOx nanosheets for the adsorption of glycerol molecules in GOR and the dissociation of water molecules in HER, as well as the strong electronic interaction with Pt. The MoOx/Pt composite thus significantly enhances the specific mass activity of Pt and the kinetics for both reactions. With MoOx/Pt electrodes serving as both cathode and anode, two-electrode glycerol electrolysis is achieved at a cell voltage of 0.70 V to reach a current density of 10 mA cm−2, which is 0.90 V less than that required for water electrolysis.
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| 7. |
- Yu, Xiaowen, et al.
(författare)
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Hydrogen Evolution Linked to Selective Oxidation of Glycerol over CoMoO4—A Theoretically Predicted Catalyst
- 2022
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 12:14
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical valorization of biomass waste (e.g., glycerol) for production of value-added products (such as formic acid) in parallel with hydrogen production holds great potential for developing renewable and clean energy sources. Here, a synergistic effort between theoretical calculations at the atomic level and experiments to predict and validate a promising oxide catalyst for the glycerol oxidation reaction (GOR) are reported, providing a good example of designing novel, cost-effective, and highly efficient electrocatalysts for producing value-added products at the anode and high-purity hydrogen at the cathode. The predicted CoMoO4 catalyst is experimentally validated as a suitable catalyst for GOR and found to perform best among the investigated metal (Mn, Co, Ni) molybdate counterparts. The potential required to reach 10 mA cm−2 is 1.105 V at 60 °C in an electrolyte of 1.0 ᴍ KOH with 0.1 ᴍ glycerol, which is 314 mV lower than for oxygen evolution. The GOR reaction pathway and mechanism based on this CoMoO4 catalyst are revealed by high-performance liquid chromatography and in situ Raman analysis. The coupled quantitative analysis indicates that the CoMoO4 catalyst is highly active toward C—C cleavage, thus presenting a high selectivity (92%) and Faradaic efficiency (90%) for formate production.
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| 8. |
- Agredano Torres, Manuel, et al.
(författare)
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Dynamic power allocation control for frequency regulation using hybrid electrolyzer systems
- 2023
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Ingår i: 2023 IEEE Applied Power Electronics Conference And Exposition, APEC. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 2991-2998
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Konferensbidrag (refereegranskat)abstract
- The increase in hydrogen production to support the energy transition in different sectors, such as the steel industry, leads to the utilization of large scale electrolyzers. These electrolyzers have the ability to become a fundamental tool for grid stability providing grid services, especially frequency regulation, for power grids with a high share of renewable energy sources. Alkaline electrolyzers (AELs) have low cost and long lifetime, but their slow dynamics make them unsuitable for fast frequency regulation, especially in case of contingencies. Proton Exchange Membrane electrolyzers (PEMELs) have fast dynamic response to provide grid services, but they have higher costs. This paper proposes a dynamic power allocation control strategy for hybrid electrolyzer systems to provide frequency regulation with reduced cost, making use of advantages of AELs and PEMELs. Simulations and experiments are conducted to verify the proposed control strategy.
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| 9. |
- Anil, Athira, et al.
(författare)
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Effect of pore mesostructure on the electrooxidation of glycerol on Pt mesoporous catalysts
- 2023
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 11:31, s. 16570-16577
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Tidskriftsartikel (refereegranskat)abstract
- Glycerol is a renewable chemical that has become widely available and inexpensive due to the increased production of biodiesel. Noble metal materials have shown to be effective catalysts for the production of hydrogen and value-added products through the electrooxidation of glycerol. In this work we develop three platinum systems with distinct pore mesostructures, e.g., hierarchical pores (HP), cubic pores (CP) and linear pores (LP); all with high electrochemically active surface area (ECSA). The ECSA-normalized GEOR catalytic activity of the systems follows HPC > LPC > CPC > commercial Pt/C. Regarding the oxidation products, we observe glyceric acid as the main three-carbon product (3C), with oxalic acids as the main two-carbon oxidation product. DFT-based theoretical calculations support the glyceraldehyde route going through tartronic acid towards oxalic acid and also help understanding why the dihydroxyacetone (DHA) route is active despite the absence of DHA amongst the observed oxidation products.
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| 10. |
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| 11. |
- Diaz-Morales, Oscar, et al.
(författare)
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Catalytic effects of molybdate and chromate–molybdate films deposited on platinum for efficient hydrogen evolution
- 2023
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Ingår i: Journal of chemical technology and biotechnology (1986). - : Wiley. - 0268-2575 .- 1097-4660. ; 98:5, s. 1269-1278
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Sodium chlorate (NaClO3) is extensively used in the paper industry, but its production uses strictly regulated highly toxic Na2Cr2O7 to reach high hydrogen evolution reaction (HER) Faradaic efficiencies. It is therefore important to find alternatives either to replace Na2Cr2O7 or reduce its concentration.RESULTS: The Na2Cr2O7 concentration can be significantly reduced by using Na2MoO4 as an electrolyte co-additive. Na2MoO4 in the millimolar range shifts the platinum cathode potential to less negative values due to an activating effect of cathodically deposited Mo species. It also acts as a stabilizer of the electrodeposited chromium hydroxide but has a minor effect on the HER Faradaic efficiency. X-ray photoelectron spectroscopy (XPS) results show cathodic deposition of molybdenum of different oxidation states, depending on deposition conditions. Once Na2Cr2O7 was present, molybdenum was not detected by XPS, as it is likely that only trace levels were deposited. Using electrochemical measurements and mass spectrometry we quantitatively monitored H2 and O2 production rates. The results indicate that 3 μmol L−1 Na2Cr2O7 (contrary to current industrial 10–30 mmol L−1) is sufficient to enhance the HER Faradaic efficiency on platinum by 15%, and by co-adding 10 mmol L−1 Na2MoO4 the cathode is activated while avoiding detrimental O2 generation from chemical and electrochemical reactions. Higher concentrations of Na2MoO4 led to increased oxygen production.CONCLUSION: Careful tuning of the molybdate concentration can enhance performance of the chlorate process using chromate in the micromolar range. These insights could be also exploited in the efficient hydrogen generation by photocatalytic water splitting and in the remediation of industrial wastewater.
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| 12. |
- Duwig, Christophe
(creator_code:cre_t)
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Exhibition : Towards the energy of the future – the invisible revolution behind the electrical socket
- 2023
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Konstnärligt arbeteabstract
- Energy Crisis! Electricity Price drama! The threat of global energy poverty! Media are generous with spectacular titles. Yes, energy is important, and yes, nearly all societal challenges are connected to how we convert, distribute and use energy. Therefore, the KTH Energy Platform and KTH Library presented an exhibition with the theme Towards the energy of the future – the invisible revolution behind the electrical socket.The exhibition displayed showcase illustrations from the book made by Lotta Waesterberg Tomasson, as well as books related to energy and electricity from the KTH Library's collections. In parallell with the exhibition, a series of live popular science lunch seminars with presentations of selected chapters of the book took place. As part of the exhibition, students from KTH's Electrical Engineering program also showcased exciting projects that connect to the anthology’s contents, made with materials and equipment from the student-driven ELAB and “Studentverkstan”. Visitors were also invited to share their reflections and ideas on energy.
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| 13. |
- Endrodi, Balazs, et al.
(författare)
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A review of chromium(VI) use in chlorate electrolysis : Functions, challenges and suggested alternatives
- 2017
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Ingår i: Electrochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-4686 .- 1873-3859. ; 234, s. 108-122
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Forskningsöversikt (refereegranskat)abstract
- Sodium chlorate is industrially produced by electrolysis of an aqueous salt solution, in which chromium ( VI) constitutes an important excipient component. It is added to a concentration of a few grams Na2Cr2O7/ liter to the electrolyte and has several functions in the process, the most important being to increase the Faradaic efficiency for hydrogen evolution in the undivided electrochemical cells. A thin film of Cr(OH)(3) x nH(2)O formed by reductive deposition on the cathodes decreases the rate of unwanted side reactions, while still enabling hydrogen evolution to occur. In addition chromium(VI) buffers the electrolyte at the optimum pH for operation and promotes the desired homogeneous reactions in the electrolyte bulk. Chromium species also affect the rates of hydrogen and oxygen evolution at the electrodes and are said to protect the steel cathodes from corrosion. Although chromium(VI) stays in a closed loop during chlorate production, chromate is a highly toxic compound and new REACH legislation therefore intends to phase out its use in Europe from 2017. A production without chromium(VI), with no other process modifications is not possible, and today there are no commercially available alternatives to its addition. Thus, there is an urgent need for European chlorate producers to find solutions to this problem. It is expected that chromium-free production will be a requirement also in other parts of the world, following the European example. As the chromium(VI) addition affects the chlorate process in many ways its replacement might require a combination of solutions targeting each function separately. The aim of this paper is to explain the role and importance of chromium(VI) in the chlorate manufacturing process. Previous achievements in its replacement are summarized and critically evaluated to expose the current state of the field, and to highlight the most promising avenues to be followed. An attempt is also made to reveal connections with other research fields (e.g. photochemical water splitting, corrosion science) facing similar problems. Allied effort of these different communities is expected to open up research avenues to the mutual benefit of these fields.
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| 14. |
- Endrodi, Balazs, et al.
(författare)
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In situ formed vanadium-oxide cathode coatings for selective hydrogen production
- 2019
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Ingår i: Applied Catalysis B. - : Elsevier. - 0926-3373 .- 1873-3883. ; 244, s. 233-239
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Tidskriftsartikel (refereegranskat)abstract
- Electrode selectivity towards hydrogen production is essential in various conversion technologies for renewable energy, as well as in different industrial processes, such as the electrochemical production of sodium chlorate. In this study we present sodium metavanadate as a solution additive, inducing selective cathodic formation of hydrogen in the presence of various other reducible species such as hypochlorite, chlorate, oxygen, nitrate, hydrogen-peroxide and ferricyanide. During electrolysis a vanadium-oxide coating forms from the reduction of sodium metavanadate, explaining the observed enhanced selectivity. The hydrogen evolution reaction proceeds without significantly altered kinetics on such in situ modified electrode surfaces. This suggests that the reaction takes place at the interface between the electrode surface and the protective film, which acts as a diffusion barrier preventing the unwanted species to reach the electrode surface.
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| 15. |
- Endrodi, Balazs, et al.
(författare)
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Selective electrochemical hydrogen evolution on cerium oxide protected catalyst surfaces
- 2020
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 341
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Tidskriftsartikel (refereegranskat)abstract
- To date the only known solution to avoid the unwanted electrochemical reduction of hypochlorite and chlorate in industrial chlorate production, performed in undivided cells, is the addition of dichromate to the chlorate electrolyte. Because of the toxicity of this compound its use is restricted within the European Union to time limited authorization by REACH. Therefore, an alternative to sodium dichromate is essential to maintain, or even increase the process efficiency. The addition of cerium (III) salts to a hypochlorite solution increases the cathodic selectivity towards hydrogen evolution (HER), the preferred cathode process in industrial chlorate production. This is attributed to the deposition of a thin cerium oxide/hydroxide coating on the cathode, induced by the increased local alkalinity during electrolysis. Performing the electrodeposition of such protective coating ex situ, well-controlled coating thickness can be achieved. Optimizing the deposition conditions (time, current density), a coherent and stable coating is formed on the electrode surface. On this protected electrode surface the electrochemical reduction of hypochlorite is suppressed by ca. 90% compared to the bare Pt electrode, while the HER proceeds with high selectivity and unchanged kinetics. Interestingly, other electrochemical reactions (O-2 reduction, H2O2 reduction and oxidation) are also suppressed by the protective coating, suggesting that the deposited layer acts as an inorganic membrane on the electrode surface.
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| 16. |
- Endrodi, Balazs, et al.
(författare)
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Selective Hydrogen Evolution on Manganese Oxide Coated Electrodes : New Cathodes for Sodium Chlorate Production
- 2019
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 7:14, s. 12170-12178
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Tidskriftsartikel (refereegranskat)abstract
- The safety and feasibility of industrial electrochemical production of sodium chlorate, an important chemical in the pulp and paper industry, depend on the selectivity of the electrode processes. The cathodic reduction of anodic products is sufficiently suppressed in the current technology by the addition of chromium(VI) to the electrolyte, but due to the high toxicity of these compounds, alternative pathways are required to maintain high process efficiency. In this paper, we evaluate the electrochemical hydrogen evolution reaction kinetics and selectivity on thermally formed manganese oxide-coated titanium electrodes in hypochlorite and chlorate solutions. The morphology and phase composition of manganese oxide layers were varied via alteration of the annealing temperature during synthesis, as confirmed by scanning electron microscopy, X-ray diffraction, synchrotron radiation X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy measurements. As shown in mass spectroscopy coupled electrochemical measurements, the hydrogen evolution selectivity in hypochlorite and chlorate solutions is dictated by the phase composition of the coating. Importantly, a hydrogen evolution efficiency of above 95% was achieved with electrodes of optimized composition (annealing temperature, thickness) in hypochlorite solutions. Further, these electrode coatings are nontoxic and Earth-abundant, offering the possibility of a more sustainable chlorate production.
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| 17. |
- Endrodi, Balázs, et al.
(författare)
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Suppressed oxygen evolution during chlorateformation from hypochlorite in the presenceof chromium(VI)
- 2019
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Ingår i: Journal of chemical technology and biotechnology (1986). - : Wiley. - 0268-2575 .- 1097-4660. ; 94:5, s. 1520-1527
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Chromium(VI) is a crucial electrolyte component in industrial chlorate production. Due to its toxicity, iturgently needs to be abandoned and its functions fulfilled by new solutions. In the industrial production of sodium chlorate,homogeneous decomposition of the hypochlorite intermediate to chlorate is a key step. As a competing loss reaction,hypochlorite can decompose to oxygen. How chromium(VI) affects these reactions is not well understood.RESULTS: This work shows, for the first time, that chromium(VI) selectively accelerates the chlorate formation from hypochloriteboth in dilute and concentrated, industrially relevant solutions. The effect of the ionic strength and the specific contributionof different electrolyte components were systematically studied. By simultaneously measuring the concentration decayof hypochlorite (UV–vis spectroscopy) and the oxygen formation (mass spectrometry), both the rate and the selectivity of thereactions were evaluated.CONCLUSION: In the presence of chromium(VI) the hypochlorite decomposition is described by the sum of an uncatalyzedand a parallel catalyzed reaction, where oxygen only forms in the uncatalyzed reaction. When removing chromium(VI),the homogeneous oxygen formation increases, causing economic and safety concerns. The need for a catalyst selectivefor chlorate formation is emphasized.
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| 18. |
- khataee, Amirreza, et al.
(författare)
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Anion exchange membrane water electrolysis using Aemion™ membranes and nickel electrodes
- 2022
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 10:30, s. 16061-16070
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Tidskriftsartikel (refereegranskat)abstract
- Anion exchange membrane water electrolysis (AEMWE) is a potentially low-cost and sustainable technology for hydrogen production that combines the advantages of proton exchange membrane and traditional alkaline water electrolysis systems.
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| 19. |
- Kim, Hyeyun, 1986-, et al.
(författare)
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Feasibility of chemically modified cellulose nanofiber membrane as lithium ion battery separator
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Chemical modification of cellulose contributes to its fibrillation to nanofibers and consequently production of a mesoporous membrane, desirable for lithium ion battery separator. Nevertheless, the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidized cellulose nanofibers (TOCN) based separator with high charge density (650 μmol COO-/gCNF) has high risk of cell failure in lithium ion battery (LIB), compared to the counterpart with lower charge density (350 μmol/g). In this study, the influence of sodium carboxylate or carboxylic acid functional groups in TOCN as lithium ion battery separator was investigated. In-operando mass spectrometry measurements were used to elucidate the cause of cell failure by analyzing the gas evolved, from batteries containing different types of separators. For the TOCN separator with sodium carboxylate functional groups, it seems that Na deposition is the dominant reason for poor electrochemical stability of the cell thereof. The poor performance of the protonated TOCN separator is attributed to a high amount of gas evolution, mostly H2, originating from the reduction of trace water and H+ released from COOH and OH surface groups. Nonetheless, the electrochemical performance of the separator could be dramatically improved by adding 2 wt% of vinylene carbonate (VC) to the electrolyte, which effectively suppressed the generation of gas. Furthermore, the separator demonstrated excellent cycling stability in the pouch cell and sufficiently high specific capacity at ≈ 2C of discharging rate.
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| 20. |
- Kim, Hyeyun, 1986-, et al.
(författare)
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Feasibility of Chemically Modified Cellulose Nanofiber Membranes as Lithium-Ion Battery Separators
- 2020
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 12:37, s. 41211-41222
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Tidskriftsartikel (refereegranskat)abstract
- Chemical modification of cellulose is beneficial to produce highly porous lithium-ion battery (LIB) separators, but introduction of high charge density adversely affects its electrochemical stability in a LiNi1/3Mn1/3Co1/3O2 (NMC)/graphite full cell. In this study, the influence of carboxylate functional groups in 2,2,6,6-tetramethylpiperidine-1-oxyl-mediated oxidized cellulose nanofibers (TOCNs) on the electrochemical performances of the LIB separator was investigated. X-ray photoelectron spectroscopy and in operando mass spectrometry measurements were used to elucidate the cause of failure of the batteries containing TOCN separators in the presence and absence of sodium counterions in the carboxylate groups and additives. For the TOCN separator with sodium carboxylate functional groups, it seems that Na deposition is the dominant reason for poor electrochemical stability of the cell thereof. The poor performance of the protonated TOCN separator, attributed to a high amount of gas evolution, is dramatically improved by adding 2 wt % of vinylene carbonate (VC) because of suppressed gas evolution. Unveiling the failure mechanism of the TOCN separators and successively implementing the strategies to improve performance, for example, removing Na, adding VC, and adjusting cycling rates, enable a remarkable cycling performance in the NMC/graphite full cell at approximate to 2 C (3 mA/cm(2)) of a fast discharging rate. Despite the aforementioned efforts and compromises required, an increased charge density of the TOCN is beneficial to acquire a mechanically stronger separator. In conclusion, the manufacturing process of cellulose nanofibers needs to be carefully adjusted to acquire a desired separator property. To the best of our knowledge, it is first reported to perform operando gas evolution measurements to systematically investigate the electrochemical stability of nanocellulose as an LIB separator material. The results elucidate not only the challenges for extensive applications of hygroscopic biomaterials for commercial LIBs but also the practical solutions to achieve high electrochemical stability of the materials.
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| 21. |
- Kim, Hyeyun, et al.
(författare)
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Lithium Ion Battery Separators Based On Carboxylated Cellulose Nanofibers From Wood
- 2019
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 2:2, s. 1241-1250
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Tidskriftsartikel (refereegranskat)abstract
- Carboxylated cellulose nanofibers, prepared by TEMPO-mediated oxidation (TOCN), were processed into asymmetric mesoporous membranes using a facile paper-making approach and investigated as lithium ion battery separators. Membranes made of TOCN with sodium carboxylate groups (TOCN-COO-Na+) showed capacity fading after a few cycles of charging and discharging. On the other hand, its protonated counterpart (TOCN-COOH) showed highly improved electrochemical and cycling stability, displaying 94.5% of discharge capacity maintained after 100 cycles at 1 C rate of charging and discharging. The asymmetric surface porosity of the membranes must be considered when assembling a battery cell as it influences the rate capabilities of the battery. The wood-based TOCN-membranes have a good potential as an ecofriendly alternative to conventional fossil fuel-derived separators without adverse side effects.
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| 22. |
- Kim, Hyeyun, 1986-, et al.
(författare)
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One-step electro-precipitation of nanocellulose hydrogels on conducting substrates and its possible applications : coatings, composites, and energy devices
- 2019
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 7:24, s. 19415-19425
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Tidskriftsartikel (refereegranskat)abstract
- TEMPO-oxidized cellulose nanofibrils (TOCN) are pH-responsive biopolymers which undergo sol–gel transition at acidic conditions (pH < 4) due to charge neutralization. Electronically conducting materials can be coated by such gels during aqueous electrolysis, when an electrochemical reaction generates a local pH decrease at the electrode surface. In this work, electro-precipitation of different TOCN gels has been performed on oxygen evolving anodes. We demonstrate that TOCN hydrogels can be electrochemically coated on the surface of any conductive material with even complex 3D shape. Further, not only TOCN but also micro- or nanosized particles containing TOCN composites can be coated on the electrode surface, and coatings containing multiple layers of different composites can be also produced. We demonstrate that this simple and facile electrocoating technique can be subject to various applications, such as coatings making electrodes selective for the hydrogen evolution reaction, as well as a new eco-friendly aqueous-based synthesis of Li-ion battery electrodes.
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| 23. |
- Kim, Hyeyun, 1986-, et al.
(författare)
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Spray-coated nanocellulose based separator/electrode assembly
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A separator-electrode assembly (SEA) made of wood-based cellulose nanofibers (CNF) and Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was fabricated by a facile spray-coating process. CNF building blocks were prepared by homogenizing enzymatically pretreated cellulose fibers dispersed in a non-hazardous solvent, 2-propanol (IPA). The porous composite separator was made by spray-coating thin layers CNF-IPA, followed by a PVDF-HFP spray coating, on a lithium ion battery electrode. A CNF substrate was crucial for making a highly porous and thermally stable separator and PVDF-HFP coating enhanced its mechanical stability. The SEA maintained dimensional integrity when subjected to high temperature and when used in lithium ion batteries. A CNF-LiNi1/3Co1/3Mn1/3O2 (NMC) SEA showed excellent electrochemical stability, especially at fast charging/discharging rate, whereas a graphite counterpart showed poor electrochemical performance, resulting in cell failure. A SiO2 layer overcoated on the top of CNF-NMC SEA enabled its application for a proof-of-concept lithium metal battery and for a high energy‐density LiNi0.6Co0.2Mn0.2O2 (NMC622) lithium‐ion battery with excellent electrochemical stability and performances. The utilization of biodegradable materials and non-hazardous solvents such as IPA and acetone makes the development of the CNF based SEA attractive, as an eco-friendly lithium ion battery manufacturing process.
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| 24. |
- Kim, Hyeyun, 1986-
(författare)
-
Wood-Based Nanocellulose In Lithium Ion Batteries and Electrochemical Coatings
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium ion batteries contain diverse functional polymeric materials, e.g. binders and separators. Naturally self-assembled wood cellulose can be disintegrated to nanosized particles with a diversity of morphology by top-down processes, adjusting the manufacturing parameters. The nanomaterials can then be reconstructed by bottom-up assembly to structures similar to that of the polymeric materials in lithium ion batteries, capable of replacing their functions and ensuring similar or improved performance.The aim of the thesis is to evaluate the feasibility of wood-based cellulose nanofibers in lithium ion batteries and explore other possible applications. The relationship between the characteristics of nanocellulose, treated by different processes, and their performance as battery components were investigated using electrochemical and in-operando measurements. Development of electrode-integrated cellulose separators was enabled by a non-aqueous drying method. This significantly improved the drying efficiency and can be considered an eco-friendly process without using hazardous chemicals. This study sheds the light on cellulose as a promising separator material, satisfying the industrial needs without trade-off of durability of the material and ion transport properties.Other than lithium ion battery applications, cellulose nanofibrils are introduced as a pH-responsive polymer and a precursor of hydrogel, electrochemically coated on any conductive substrate. Not only hydrogel, this electro-precipitation method also enables to fabricate single or multi-layered composites. The hydrogel and the composites fabricated by this technique can work as functional materials in the diverse electrochemical applications.In summary, the results indicate that using wood-based cellulose as a raw material is beneficial to fabricate the functional materials by eco-friendly manufacturing processes, available for a variety of electrochemical applications, showing excellent performance.
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| 25. |
- Krüger, Andries, et al.
(författare)
-
Integration of water electrolysis for fossil-free steel production
- 2020
-
Ingår i: International journal of hydrogen energy. - : Elsevier Ltd. - 0360-3199 .- 1879-3487. ; 45:55, s. 29966-29977
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigates the integration of water electrolysis technologies in fossil-free steelmaking via the direct reduction of iron ore followed by processing in an electric arc furnace (EAF). Hydrogen (H2) production via low or high temperature electrolysis (LTE and HTE) is considered for the production of carbon-free direct reduced iron (DRI). The introduction of carbon into the DRI reduces the electricity demand of the EAF. Such carburization can be achieved by introducing carbon monoxide (CO) into the direct reduction process. Therefore, the production of mixtures of H2 and CO using either a combination of LTE coupled with a reverse water-gas shift reactor (rWGS-LTE) or high-temperature co-electrolysis (HTCE) was also investigated. The results show that HTE has the potential to reduce the specific electricity consumption (SEC) of liquid steel (LS) production by 21% compared to the LTE case. Nevertheless, due to the high investment cost of HTE units, both routes reach similar LS production costs of approximately 400 €/tonne LS. However, if future investment cost targets for HTE units are reached, a production cost of 301 €/tonne LS is attainable under the conditions given in this study. For the production of DRI containing carbon, a higher SEC is calculated for the LTE-rWGS system compared to HTCE (4.80 vs. 3.07 MWh/tonne LS). Although the use of HTCE or LTE-rWGS leads to similar LS production costs, future cost reduction of HTCE could result in a 10% reduction in LS production cost (418 vs. 375 €/tonne LS). We show that the use of HTE, either for the production of pure H2 or H2 and CO mixtures, may be advantageous compared to the use of LTE in H2-based steelmaking, although results are sensitive to electrolyzer investment costs, efficiencies, and electricity prices.
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| 26. |
- Lind, Elvira, et al.
(författare)
-
Catalyst layer utilisation during glycerol electrooxidation in alkaline media with electrodeposited Pd catalysts at different thicknesses
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The glycerol electrooxidation reaction (GEOR) has been increasingly studied for providing value-added chemical products whilst also facilitating a concurrent reduction process such as hydrogen evolution. Noble metals have been shown to be highly active for the GEOR in alkaline media. Here, to assess the effects of mass transport, catalyst layer thickness and pH on the GEOR, three thicknesses of Pd are electrodeposited onto a Ni rotating disk electrode and studied for a constant glycerol concentration of 0.50 M with NaOH to glycerol ratios of 1:2, 1:1 and 2:1. The electrodeposited catalysts are found to be morphologically similar with similar crystallographic structures. The activity, evaluated from the peak current density at the point of deactivation, shows that for every pH, the thinnest catalyst has the highest specific activity, whereas the thickest catalyst has the lowest. Therefore, there is a significant underutilisation of the thicker porous Pd electrodes for the GEOR. The thinnest catalyst layer is furthermore investigated in a solution of 1.0 M NaOH and 1.0 M glycerol. The doubling of the glycerol concentration in this case did not provide a significant increase in current density. Therefore, we propose that there is an optimal ratio of OHˉ to glycerol ratio in solution of around 2:1 due to the stoichiometry of the GEOR with the diffusion layer thickness and flux at higher glycerol concentrations considered.
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| 27. |
- Lindberg, Aleksandra, 1990-, et al.
(författare)
-
Sources of Oxygen Produced in the Chlorate Process Utilizing Dimensionally Stable Anode (DSA) Electrodes Doped by Sn and Sb
- 2021
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 60:37, s. 13505-13514
-
Tidskriftsartikel (refereegranskat)abstract
- Identifying the sources of oxygen in the chlorate process is challenging due to the complex set of chemical and electrochemical reactions involved. Here, two types of electrodes have been investigated-Ti0.7Ru0.3Ox, and electrodes with aimed composition Ti0.34Ru0.3Sn0.3Sb0.06Ox, both compared with platinum anodes. The cell oxygen off-gas was analyzed employing mass spectrometry together with ex situ UV-vis spectroscopy to quantify the kinetic rate constants. Noteworthy is that the respective rates of oxygen formation from anodic and chemical reactions in the presence of hypochlorite are of the same magnitude. The addition of Sn and Sb doubled the surface area of the electrodes and decreased oxygen production when electrodes were used for the first time. However, rate constants for total oxygen production with reused electrodes follow the trend: homogeneous hypochlorite decomposition < TiRu < TiRuSnSb to the highest value obtained by Pt. The same trend is noticed for rate constants concerning the hypochlorite decomposition.
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| 28. |
- Lindberg, Aleksandra, 1990-, et al.
(författare)
-
Sources of oxygen produced in the chlorate process utilizing DSA electrodes doped by Sn and Sb
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Identifying the sources of oxygen in the chlorate process is challenging due to the complex set of chemical and electrochemical reactions involved. Here, two types of electrodes have been investigated -Ti0.7Ru0.3Ox, and electrodes with aimed composition Ti0.34Ru0.3Sn0.3Sb0.06Ox, both compared with platinum anodes. The cell oxygen off-gas was analyzed employing mass spectrometry together with ex-situ UV-Vis spectroscopy to quantify the kinetic rate constants. Noteworthy is that the respective rates of oxygen formation from anodic and chemical reactions in the presence of hypochlorite are of the same magnitude. The addition of Sn and Sb doubled the surface area of the electrodes and decreased oxygen production when electrodes were used for the first time. However, rate constants for total oxygen production with reused electrodes, follow the trend: homogenous hypochlorite decomposition < TiRu < TiRuSnSb to the highest value obtained by Pt. The same trend is noticed for rate constants concerning the hypochlorite decomposition.
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| 29. |
- Lindberg, Jonas, 1988-
(författare)
-
Electrochemical Investigation of the Reaction Mechanism in Lithium-Oxygen Batteries
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium-oxygen batteries, also known as Lithium-air batteries, could possibly revolutionize energy storage as we know. By letting lithium react with ambient oxygen gas very large theoretical energy densities are possible. However, there are several challenges remaining to be solved, such as finding suitable materials and understanding the reaction, before the lithium-oxygen battery could be commercialized. The scope of this thesis is focusing on the latter of these challenges.Efficient ion transport between the electrodes is imperative for all batteries that need high power density and energy efficiency. Here the mass transport properties of lithium ions in several different solvents was evaluated. The results showed that the lithium mass transport in electrolytes based on the commonly used lithium-oxygen battery solvent dimethyl sulfoxide (DMSO) was very similar to that of conventional lithium-ion battery electrolytes. However, when room temperature ionic liquids were used the performance severely decreased.Addition of Li salt will effect the oxygen concentration in DMSO-based electrolytes. The choice of lithium salt influenced whether the oxygen concentration increased or decreased. At one molar salt concentration the highest oxygen solubility was 68 % larger than the lowest one.Two model systems was used to study the electrochemical reaction: A quartz crystal microbalance and a cylindrical ultramicroelectrode. The combined usage of these systems showed that during discharge soluble lithium superoxide was produced. A consequence of this was that not all discharge product ended up on the electrode surface.During discharge the cylindrical ultramicroelectrodes displayed signs of passivation that previous theory could not adequately describe. Here the passivation was explained in terms of depletion of active sites. A mechanism was also proposed.The O2 and Li+ concentration dependencies of the discharge process were evaluated by determining the reactant reaction order under kinetic and mass transport control. Under kinetic control the system showed non-integer reaction orders with that of oxygen close to 0.5 suggesting that the current determining step involves adsorption of oxygen. At higher overpotentials, at mass transport control, the reaction order of lithium and oxygen was zero and one, respectively. These results suggest that changes in oxygen concentration will influence the current more than that of lithium.During charging not all of the reaction product was removed. This caused an accumulation when several cycles was examined. The charge reaction pathway involved de-lithiation and bulk oxidation, it also showed an oxygen concentration dependence.
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| 30. |
- Lindberg, Jonas, et al.
(författare)
-
Li Salt Anion Effect on O-2 Solubility in an Li-O-2 Battery
- 2018
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:4, s. 1913-1920
-
Tidskriftsartikel (refereegranskat)abstract
- For the promising Li-O-2 battery to be commercialized, further understanding of its constituents is needed. This study deals with the role of O-2 in Li-O-2 batteries, both its influence on electrochemical performance and its solubility in lithium-salt-containing dimethyl sulfoxide (DMSO) electrolytes. Experimentally, the electrochemical performance was evaluated using cylindrical ultramicroelectrodes. Two independent techniques, using a mass spectrometer and an optical sensor, were used to evaluate the O-2 solubility, expressed as Henry's constant. Furthermore, the ionic conductivity, dynamic viscosity, and density were also measured. Density functional theory calculations were made of the interaction energy between O-2 and the different species in the electrolytes. When varying O-2 partial pressure, the current was larger at high pressures confirming that the O-2 concentration is of key importance when studying the kinetics of this system. Compared with neat DMSO, the O-2 solubility increased with addition of LiTFSI and decreased with addition of LiClO4, indicating that the salt influences the solubility. This solubility trend is best explained in terms of apparent molar volume and interaction energy between O-2 and the salt anion. In conclusion, this study shows the importance of O-2 concentration, not just its partial pressure, and that the choice of Li salt can make this concentration increase or decrease.
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| 31. |
- Lu, Huiran, et al.
(författare)
-
Effects of Different Manufacturing Processes on TEMPO-Oxidized Carboxylated Cellulose Nanofiber Performance as Binder for Flexible Lithium-Ion Batteries
- 2017
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:43, s. 37712-37720
-
Tidskriftsartikel (refereegranskat)abstract
- Carboxylated cellulose nanofibers (CNF) prepared using the TEMPO-route are good binders of electrode components in flexible lithium-ion batteries (LIB). However, the different parameters employed for the defibrillation of CNF such as charge density and degree of homogenization affect its properties when used as binder. This work presents a systematic study of CNF prepared with different surface charge densities and varying degrees of homogenization and their performance as binder for flexible LiFePO4 electrodes. The results show that the CNF with high charge density had shorter fiber lengths compared with those of CNF with low charge density, as observed with atomic force microscopy. Also, CNF processed with a large number of passes in the homogenizer showed a better fiber dispersibility, as observed from rheological measurements. The electrodes fabricated with highly charged CNF exhibited the best mechanical and electrochemical properties. The CNF at the highest charge density (ISSO mu mol g(-1)) and lowest degree of homogenization (3 + 3 passes in the homogenizer) achieved the overall best performance, including a high Young's modulus of approximately 311 MPa and a good rate capability with a stable specific capacity of 116 mAh g(-1) even up to 1 C. This work allows a better understanding of the influence of the processing parameters of CNF on their performance as binder for flexible electrodes. The results also contribute to the understanding of the optimal processing parameters of CNF to fabricate other materials, e.g., membranes or separators.
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| 32. |
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| 33. |
- Lu, Huiran, et al.
(författare)
-
Flexible and Lightweight Lithium-Ion Batteries Based on Cellulose Nanofibrils and Carbon Fibers
- 2018
-
Ingår i: BATTERIES-BASEL. - : MDPI. - 2313-0105. ; 4:2
-
Tidskriftsartikel (refereegranskat)abstract
- Flexible, low-weight electrodes with integrated current collectors based on chopped polyacrylonitrile carbon fibers (CF) were produced using an easy, aqueous fabrication process, where only 4 wt% of TEMPO-oxidized cellulose nanofibrils (CNF) were used as the binder. A flexible full cell was assembled based on a LiFePO4 (LFP) positive electrode with a CF current collector and a current collector-free CF negative electrode. The cell exhibited a stable specific capacity of 121 mAh g(-1) based on the LFP weight. The CF in the negative electrode acted simultaneously as active material and current collector, which has a significant positive impact on energy density. Stable specific capacities of the CF/CNF negative electrode of 267 mAh g(-1) at 0.1 C and 150 mAh g(-1) at 1 C are demonstrated. The LFP/CNF with CF/CNF, as the current collector positive electrode (LFP-CF), exhibited a good rate performance with a capacity of -150 mAh g(-1) at 0.1 C and 133 mAh g(-1) at 1 C. The polarization of the LFP-CF electrode was similar to that of a commercial Quallion LFP electrode, while much lower compared to a flexible LFP/CNF electrode with Al foil as the current collector. This is ascribed to good contact between the CF and the active material.
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| 34. |
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| 35. |
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| 36. |
- Martín-Yerga, Daniel, et al.
(författare)
-
Effects of Incorporated Iron or Cobalt on the Ethanol Oxidation Activity of Nickel (Oxy)Hydroxides in Alkaline Media
- 2019
-
Ingår i: Electrocatalysis. - : Springer Science and Business Media LLC. - 1868-2529 .- 1868-5994.
-
Tidskriftsartikel (refereegranskat)abstract
- Nickel (oxy)hydroxides (NiOxHy) are promising cost-effective materials that exhibit a fair catalytic activity for the ethanol oxidation reaction (EOR) and could be used for sustainable energy conversion. Doping the NiOxHy structure with other metals could lead to enhanced catalytic properties but more research needs to be done to understand the role of the doping metal on the EOR. We prepared NiOxHy films doped with Fe or Co with different metallic ratios by electrodeposition and evaluated the EOR. We found a positive and negative effect on the catalytic activity after the incorporation of Co and Fe, respectively. Our results suggest that Ni atoms are the active sites for the EOR since Tafel slopes were similar on the binary and pristine nickel (oxy)hydroxides and that the formal potential of the Ni(II)/Ni(III) redox couple is a good descriptor for the EOR activity. This work also highlights the importance of controlled metal doping on catalysts and may help in the design and development of improved materials for the EOR.
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| 37. |
- Martín-Yerga, Daniel, et al.
(författare)
-
In situ catalyst reactivation for enhancing alcohol electro-oxidation and coupled hydrogen generation
- 2020
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 56:28, s. 4011-4014
-
Tidskriftsartikel (refereegranskat)abstract
- A novel method exploiting the in situ reactivation of a PdNi catalyst to enhance the electro-oxidation of alcohols is reported. The periodic regeneration of the catalyst surface leads to significant gains in terms of conversion rate, energy requirements and stability compared to the conventional potentiostatic method.
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| 38. |
- Martin-Yerga, Daniel, et al.
(författare)
-
Insights on the ethanol oxidation reaction at electrodeposited PdNi catalysts under conditions of increased mass transport
- 2021
-
Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 46:2, s. 1615-1626
-
Tidskriftsartikel (refereegranskat)abstract
- The development of high-performance electrocatalysts for alcohol oxidation is still a major challenge to use these reactions for sustainable energy applications such as hydrogen production. In addition, understanding the reactivity under different hydrodynamic conditions is essential since the fuel is continuously fed to the anode in practical applications. In this work, the synthesis, characterization and electroactivity of bimetallic PdNi nano-coatings generated by electrodeposition toward the ethanol oxidation reaction (EOR) is described. A catalyst formed by Pd0.91Ni0.09 nanoflowers showed the highest EOR activity and enhanced performance under moderate mass transport rate. Both OH- concentration and hydrodynamics affected the EOR activity and the product selectivity. Acetic acid was the main EOR product, but acetaldehyde formation increased when OH- was limiting or under faster mass transport rates. This study provides novel knowledge to understand the EOR on PdNi catalysts and exposes the importance of evaluating hydrodynamic conditions when developing new electrocatalysts.
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| 39. |
- Martín-Yerga, Daniel, et al.
(författare)
-
Structure–Reactivity Effects of Biomass-based Hydroxyacids for Sustainable Electrochemical Hydrogen Production
- 2021
-
Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 14:8, s. 1902-1912
-
Tidskriftsartikel (refereegranskat)abstract
- Biomass electro-oxidation is a promising approach for the sustainable generation of H2 by electrolysis with simultaneous synthesis of value-added chemicals. In this work, the electro-oxidation of two structurally different organic hydroxyacids, lactic acid and gluconic acid, was studied comparatively to understand how the chemical structure of the hydroxyacid affects the electrochemical reactivity under various conditions. It was concluded that hydroxyacids such as gluconic acid, with a considerable density of C−OH groups, are highly reactive and promising for the sustainable generation of H2 by electrolysis at low potentials and high conversion rates (less than −0.15 V vs. Hg/HgO at 400 mA cm−2) but with low selectivity to specific final products. In contrast, the lower reactivity of lactic acid did not enable H2 generation at very high conversion rates (<100 mA cm−2), but the reaction was significantly more selective (64 % to pyruvic acid). This work shows the potential of biomass-based organic hydroxyacids for sustainable generation of H2 and highlights the importance of the chemical structure on the reactivity and selectivity of the electro-oxidation reactions.
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| 40. |
- Qiu, Zhen, et al.
(författare)
-
Green hydrogen production via electrochemical conversion of components from alkaline carbohydrate degradation
- 2022
-
Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 47:6, s. 3644-3654
-
Tidskriftsartikel (refereegranskat)abstract
- Water electrolysis is a promising approach for the sustainable production of hydrogen, however, the unfavorable thermodynamics and sluggish kinetics of oxygen evolution reaction (OER) are associated with high anodic potentials. To lower the required potentials, an effective strategy is proposed to substitute OER with partial oxidation of degradation products of carbohydrate origin from the waste stream of a chemical pulping industry. In this work, two different catalytic materials - PdNi and NiO are investigated comparatively to understand their catalytic performance for the oxidation of carbohydrate alkaline degradation products (CHADs). PdNi can catalyze CHADs with low potential requirements (-0.11 V vs. Hg/HgO at 150 mA cm(-2)) but is limited to current densities <200 mA cm(-2). In contrast, NiO can operate at very high current densities but required relatively higher potentials (0.53 V vs. Hg/HgO at 500 mA cm(-2)). The performance of this non-noble metal catalyst compares favorably with that of Pd-based catalysts for hydrogen production from CHADs at high conversion rates. This work shows the potential to utilize waste streams from a large-scale process industry for sustainable hydrogen production, and also opens up opportunities to study earth-abundant electrocatalysts to efficiently oxidize biomass-derived substances.
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| 41. |
- Rossini, Matteo, et al.
(författare)
-
Rational design of membrane electrode assembly for anion exchange membrane water electrolysis systems
- 2024
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 614
-
Tidskriftsartikel (refereegranskat)abstract
- Anion exchange membrane water electrolysis (AEMWE) is a promising and potentially low-cost technology for producing green hydrogen, but a novel manufacturing technique with rational design of the electrodes is essential to improve the performance and stability. In this work, we investigate the effect of electrode structure on activity and the stability of AEMWEs by fabricating membrane electrode assemblies (MEAs). For the first time, the decal transfer method with platinum-group-metal-free (PGM-free) catalyst was successfully used in AEMWEs. With this method, deposition of a compact catalyst layer (CL) on the membrane was achieved without damaging neither the CL nor the membrane. The MEAs were designed for AEMWE using 1 M KOH as the electrolyte and the ionomer content was optimized for both cathode and anode. In the anode, a low ionomer loading improved activity and ionic conductivity, however, a higher ionomer content was beneficial for the cathode. Furthermore, the type of ionomer on the anode side has shown to be the major reason of loss of performance over time. An ionomer with low (1.4–1.7 meq g−1) Ion Exchange Capacity (IEC) and Nafion™ ionomer greatly improved the stability.
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| 42. |
- Sandin, Staffan, 1984-, et al.
(författare)
-
Deactivation and selectivity for electrochemical ozone production at Ni- and Sb-doped SnO2 / Ti electrodes
- 2020
-
Ingår i: Electrochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-4686 .- 1873-3859. ; 335
-
Tidskriftsartikel (refereegranskat)abstract
- This work reports on a time-resolved study of the deactivation of electrochemical ozone production (EOP) active anodes using a novel approach to measure total ozone production. The reproducibility and change of the electrodes over time have been investigated using a number of electrochemical and physical techniques. The dissolution of antimony from the surface of the nickel- and antimony-doped tin oxide (NATO) electrode is the main process behind the deactivation of the EOP. When surface antimony is depleted, the continued deactivation seems to be connected to the dissolution of nickel. Despite tin (from the coating) and titanium (from the substrate) continuously dissolving during galvanostatic polarization of the NATO electrode, our experiments point to no connection between these processes and the EOP activity. In addition, the selectivity of the electrode is affected by electrolyte penetration, accessing fresh reaction sites that are active on the EOP. The results indicate that both antimony (III) and nickel present at the surface of the NATO are responsible for the EOP activity.
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| 43. |
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| 44. |
- Sandin, Staffan, et al.
(författare)
-
Deposition efficiency in the preparation of ozone-producing nickel and antimony doped tin oxide anodes
- 2017
-
Ingår i: Journal of Electrochemical Science and Engineering. - : INT ASSOC PHYSICAL CHEMISTS-IAPC. - 1847-9286. ; 7:1, s. 51-64
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of precursor salts in the synthesis of nickel and antimony doped tin oxide (NATO) electrodes using thermal decomposition from dissolved chloride salts was investigated. The salts investigated were SnCl4 center dot 5H(2)O, SnCl2 center dot 2H(2)O, SbCl3 and NiCl2 center dot 6H(2)O. It was shown that the use of SnCl4 center dot 5H(2)0 in the preparation process leads to a tin loss of more than 85 %. The loss of Sb can be as high as 90 % while no indications of Ni loss was observed. As a consequence, the concentration of Ni in the NATO coating will be much higher than in the precursor solution. This high and uncontrolled loss of precursors during the preparation process will lead to an unpredictable composition in the NATO coating and will have negative economic and environmental effects. It was found that using SnCl2 center dot 2H(2)0 instead of SnCl4 center dot 5H(2)O can reduce the tin loss to less than 50 %. This tin loss occurs at higher temperatures than when using SnCl4 center dot 5H(2)O where the tin loss occurs from 56 - 147 degrees C causing the composition to change both during the drying (80 - 110 degrees C) and calcination (460 - 550 degrees C) steps of the preparation process. Electrodes coated with NATO based on the two different tin salts were investigated for morphology, composition, structure, and ozone electrocatalytic properties.
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| 45. |
- Sandin, Staffan, 1984-
(författare)
-
Oxygen formation in the chlorate process and preparation and deactivation of ozone selective anodes
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents experimental studies concerning two differ-ent electrolytic processes. One part deals with the electrochemicalformation of ozone and focuses on the preparation and deactiva-tion of a highly ozone-selective metal oxide anode (NATO - nickeland antimony doped tin oxide). The preparation of this anode bythermal decomposition of metal chloride salts was investigated anddifficulties and complications of common procedures were identi-fied. The same anodes were also studied regarding the deactivationof their ozone selective properties, identifying possible underlyingmechanisms for this as well as providing indications of the ozoneformation mechanism on the anode. When preparing these anodesby thermal decomposition, the volatility of the precursor salt usedfor the different components needs to be considered. For instanceextensive evaporation of the precursors of tin and antimony canlead to an unreliable preparation process resulting in the difficultyof controlling the properties of the prepared electrodes and a poorreproducibility of the process. The deactivation of the NATOelectrodes was investigated using the ozone current efficiency as amain indicator. The electrodes and the electrolyte were examinedusing electrochemical as well as physical techniques after differentperiods of galvanostatic polarization. The main mechanism behindthe deactivation was identified as the dissolution of antimony fromthe electrode surface. Also contributing, but not as detrimental,seems to be the dissolution of nickel. Both dopants, Ni and Sb, arepresent at the surface of the oxide anode and both seem equallyimportant for enabling the electrochemical ozone formation.The second part of this thesis concerns the decomposition ofhypochlorite, an important intermediate in the industrial chlorateprocess. A connection was found between the formation of chlorateand oxygen, both occurring according to 3rd order kinetics withregard to hypochlorite and both having their highest rates atpH 6 - 7. In the presence of chromium(VI) the hypochloritedecomposition can be modelled as the sum of two parallel reactions:one catalyzed by chromium(VI) and one uncatalyzed reaction.The byproduct oxygen seems to be formed only in the latter. Thusvaddition of chromium(VI) in the electrolyte increases both therate and the selectivity of chlorate formation. These findings areimportant as chromium(VI) needs to be removed from the processdue to its toxicity and in its absence the uncatalyzed decompositionpath would lead to an increase in oxygen formation, resultingin efficiency losses as well as potentially explosive gas mixtures.There is a need for a catalyst that can replace chromium(VI) inthis function.
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| 46. |
- Terekhina, Irina, et al.
(författare)
-
Electrocatalytic Oxidation of Glycerol to Value-Added Compounds on Pd Nanocrystals
- 2023
-
Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 6:13, s. 11211-11220
-
Tidskriftsartikel (refereegranskat)abstract
- Pd octahedral, rhombic dodecahedral, and cubic nanoparticles (PdOCTA, PdRD, and PdCUBE NPs) were synthesized, characterized, and studied as catalysts for the glycerol electrooxidation reaction (GEOR) in a strongly alkaline medium at 20 and 60 °C. The highest mass activity of 0.050 and 0.183 mA/μgPd was observed on PdOCTA at 20 and 60 °C, respectively, whereas PdCUBE exhibited the highest specific activity of 1.49 and 12.84 mA/cmPd2, respectively. The GEOR products were analyzed by high-performance liquid chromatography (HPLC), and their selectivity and overall glycerol conversion were evaluated at 0.86 V vs RHE. The selectivity toward the three-carbon chain (C3) GEOR products was similar for the different types of catalysts, with PdOCTA and PdCUBE NPs achieving more than 50% selectivity at 20 °C and more than 60% at 60 °C. Glycerate was the overall dominant product for all catalysts, with a selectivity of up to 42%. The glycerol conversion was found to be highest for PdOCTA─21% at 20 °C and 82% at 60 °C, while PdRD was the least active and showed less than 3% conversion at 20 °C and 35% at 60 °C. Based on the GEOR product distribution, a reaction mechanism was proposed.
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| 47. |
- Wang, Tongshuai, et al.
(författare)
-
Pilot-scale study of membrane-coated cathodes : Achieving high cathodic efficiency and outstanding stability in chlorate electrolysis
- 2024
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 497
-
Tidskriftsartikel (refereegranskat)abstract
- Sodium chlorate (NaClO3) is primarily used for producing chlorine dioxide, an environmentally friendly bleaching agent for pulp. Currently, dichromate is used as an electrolyte additive in the chlorate process where it has several functions, but due to health and environmental risks associated with chromate, there is a need for a less toxic alternative. In the present study, we prepared a membrane-coated cathode as a substitute for chromium(VI), to keep a high current efficiency in chlorate electrolysis. This electrode employed an industrially relevant electrode with active catalysts as the substrate and a thin layer of ion exchange polymer as the coating. The coating effectively blocked anions such as ClO− and ClO3− from reaching the cathode, thereby suppressing cathodic side reactions. We conducted a series of electrochemical characterizations on the membrane-coated cathodes with varying coating thickness and tested them in a pilot-scale setup for efficiency and stability under industrial testing conditions.
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| 48. |
- Wang, Tongshuai, et al.
(författare)
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Rational design of a membrane-coated cathode for selective electrochemical hydrogen evolution in chlorate electrolysis
- 2023
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 466, s. 143010-
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Tidskriftsartikel (refereegranskat)abstract
- The industrial chlorate process has traditionally used chromium(VI) as an electrolyte additive for high Faraday efficiency. However, due to its recognized toxicity and carcinogenic properties, the EU has regulated its usage, prompting the need for alternative approaches. In this study, we propose the adoption of a polymeric membrane-coated cathode (MCC) as a straightforward yet highly efficient solution to enhance the selectivity of the hydrogen evolution reaction (HER) in chlorate electrolysis. Proof-of-concept MCCs were fabricated by coating roughened titanium substrates with cation and anion exchange membrane layers, which function as selective barriers for anodic hypochlorite species. The study revealed that a thin membrane coating on the electrode surface effectively suppressed the permeation of anodic intermediates, without compromising the current density for HER. By optimizing the coating layer thickness and substrate surface properties of MCC, the chlorate electrolysis cell demonstrated an impressive Faradaic efficiency of up to 95% at a current density of 150 mA/cm², while maintaining exceptional stability. The outcome of this study can potentially advance the feasibility of industrial chlorate production in meeting regulatory requirements and effectively mitigating environmental consequences.
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| 49. |
- White, Jai, et al.
(författare)
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Crystallographic facet and alkali metal cation dependent glycerol electrooxidation on polycrystalline Pd probed by SECCM
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Glycerol is considered an important platform chemical for value-added organic chemical synthesis. The electrooxidation of glycerol in aqueous media provides a facile synthesis method to generate chemicals important for pharmaceutical and medical industries. Therefore, critical knowledge regarding the most active catalysts for the glycerol electrooxidation reaction (GEOR) is necessary for such a process to be viable. The GEOR on noble metals is well studied but there are significant gaps in the literature regarding the activity of specific crystal facets, particularly in the case of Pd. Through SECCM electrochemical mapping correlated with EBSD mapping to identify grain orientations, a much larger picture of the GEOR on Pd catalysts can be formed. Here, the facet dependent activity for the GEOR on Pd, evaluated through cyclic voltammetry using SECCM with co-located EBSD, is reported for the first time in alkaline solutions of KOH, NaOH and LiOH at pH 13. NaOH is shown to result in the highest performance for the GEOR and for all three electrolytes, Pd (111) provides the highest activity, Pd (001) provides intermediate to high activity and that Pd (101) is the least active. The facet dependent activity for the GEOR is directly mirrored for Pd oxidation and the subsequent PdO reduction process. Suggesting these two processes are signifiers towards catalytic activity for the GEOR.
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| 50. |
- White, Jai, et al.
(författare)
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Electrodeposited PdNi on a Ni rotating disk electrode highly active for glycerol electrooxidation in alkaline conditions
- 2022
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 403
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Tidskriftsartikel (refereegranskat)abstract
- The development of alcohol-based electrolysis to enable the concurrent production of hydrogen with low electricity consumption still faces major challenges in terms of the maximum anodic current density achievable. Whilst noble metals enable a low electrode potential to facilitate alcohol oxidation, the deactivation of the catalyst at higher potentials makes it difficult for the obtained anodic current density to compete with water electrolysis. In this work the effect of significant parameters such as mass transport, glycerol and OH- concentration and electrolyte temperature on the glycerol electrooxidation reaction (GEOR) in alkaline conditions on a bimetallic catalyst PdNi/Ni-RDE (Pd0.9Ni0.1) has been studied to discern experimental conditions which maximise achievable anodic current density before deactivation occurs. The ratio of NaOH:glycerol in the electrolyte highly affects the rate of the GEOR. A maximum current density of 793 mA cm(-2) at-0.125 V vs. Hg/HgO through steady state polarisation curves was achieved at a moderate and intermediate rotation rate of 500 RPM in a 2 M NaOH and 1 M glycerol (ratio of 2) electrolyte at 80 & DEG;C. Shown here is a method of catalyst reactivation for enabling the longterm use of the PdNi/Ni-RDE for electrolysis at optimal conditions for extended periods of time (3 h at 300 mA cm(-2) and 10 h at 100 mA cm(-2)). Through scanning electron microscopy (SEM), X-ray photon electron spectroscopy (XPS) and X-ray diffraction (XRD) it is shown that the electrodeposition of Pd and Ni forms an alloy and that after 10 h of electrolysis the catalyst has chemical and structural stability. This study provides details on parameters significant to the maximising of the GEOR current density and the minimising of the debilitating effect that deactivation has on noble metal based electrocatalysts for the GEOR.
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