| 1. |
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| 2. |
- Annamalai, Alagappan, et al.
(author)
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Influence of Sb5+ as a Double Donor on Hematite (Fe3+) Photoanodes for Surface-Enhanced Photoelectrochemical Water Oxidation
- 2018
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:19, s. 16467-16473
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Journal article (peer-reviewed)abstract
- To exploit the full potential of hematite (α-Fe2O3) as an efficient photoanode for water oxidation, the redox processes occurring at the Fe2O3/electrolyte interface need to be studied in greater detail. Ex situ doping is an excellent technique to introduce dopants onto the photoanode surface and to modify the photoanode/electrolyte interface. In this context, we selected antimony (Sb5+) as the ex situ dopant because it is an effective electron donor and reduces recombination effects and concurrently utilize the possibility to tuning the surface charge and wettability. In the presence of Sb5+ states in Sb-doped Fe2O3 photoanodes, as confirmed by X-ray photoelectron spectroscopy, we observed a 10-fold increase in carrier concentration (1.1 × 1020 vs 1.3 × 1019 cm–3) and decreased photoanode/electrolyte charge transfer resistance (∼990 vs ∼3700 Ω). Furthermore, a broad range of surface characterization techniques such as Fourier-transform infrared spectroscopy, ζ-potential, and contact angle measurements reveal that changes in the surface hydroxyl groups following the ex situ doping also have an effect on the water splitting capability. Theoretical calculations suggest that Sb5+ can activate multiple Fe3+ ions simultaneously, in addition to increasing the surface charge and enhancing the electron/hole transport properties. To a greater extent, the Sb5+- surface-doped determines the interfacial properties of electrochemical charge transfer, leading to an efficient water oxidation mechanism.
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| 3. |
- Antlauf, Mathis, et al.
(author)
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Thermal Conductivity of Cellulose Fibers in Different Size Scales and Densities
- 2021
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 22:9, s. 3800-3809
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Journal article (peer-reviewed)abstract
- Considering the growing use of cellulose in various applications, knowledge and understanding of its physical properties become increasingly important. Thermal conductivity is a key property, but its variation with porosity and density is unknown, and it is not known if such a variation is affected by fiber size and temperature. Here, we determine the relationships by measurements of the thermal conductivity of cellulose fibers (CFs) and cellulose nanofibers (CNFs) derived from commercial birch pulp as a function of pressure and temperature. The results show that the thermal conductivity varies relatively weakly with density (ρsample = 1340–1560 kg m–3) and that its temperature dependence is independent of density, porosity, and fiber size for temperatures in the range 80–380 K. The universal temperature and density dependencies of the thermal conductivity of a random network of CNFs are described by a third-order polynomial function (SI-units): κCNF = (0.0787 + 2.73 × 10–3·T – 7.6749 × 10–6·T2 + 8.4637 × 10–9·T3)·(ρsample/ρ0)2, where ρ0 = 1340 kg m–3 and κCF = 1.065·κCNF. Despite a relatively high degree of crystallinity, both CF and CNF samples show amorphous-like thermal conductivity, that is, it increases with increasing temperature. This appears to be due to the nano-sized elementary fibrils of cellulose, which explains that the thermal conductivity of CNFs and CFs shows identical behavior and differs by only ca. 6%. The nano-sized fibrils effectively limit the phonon mean free path to a few nanometers for heat conduction across fibers, and it is only significantly longer for highly directed heat conduction along fibers. This feature of cellulose makes it easier to apply in applications that require low thermal conductivity combined with high strength; the weak density dependence of the thermal conductivity is a particularly useful property when the material is subjected to high loads. The results for thermal conductivity also suggest that the crystalline structures of cellulose remain stable up to at least 0.7 GPa.
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| 4. |
- Barbero, David, et al.
(author)
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Carbon nanotube networks : nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading
- 2014
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In: Advanced Materials. - : Wiley-VCH Verlagsgesellschaft. - 0935-9648 .- 1521-4095. ; 26:19, s. 3164-
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Journal article (peer-reviewed)abstract
- Arrays of nano-engineered carbon nanotube networks embedded in nanoscale polymer structures enable highly efficient charge transport as demonstrated by D. R. Barbero and co-workers on page 3111. An increase in charge transport by several orders of magnitude is recorded at low nanotube loading compared to traditional random networks in either insulating (polystyrene) or semiconducting (polythiophene) polymers. These novel networks are expected to enhance the performance of next generation hybrid and carbon based photovoltaic devices.
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| 5. |
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| 6. |
- Barbero, David, et al.
(author)
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Nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading
- 2014
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In: Advanced Materials. - : John Wiley & Sons. - 0935-9648 .- 1521-4095. ; 26:19, s. 3111-3117
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Journal article (peer-reviewed)abstract
- We demonstrate a simple and controllable method to form periodic arrays of highly conductive nano-engineered single wall carbon nanotube networks from solution. These networks increase the conductivity of a polymer composite by as much as eight orders of magnitude compared to a traditional random network. These nano-engineered networks are demonstrated in both polystyrene and polythiophene polymers.
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| 7. |
- Barbero, David R., et al.
(author)
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Ultralow Percolation Threshold in Nanoconfined Domains
- 2017
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 11:10, s. 9906-9913
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Journal article (peer-reviewed)abstract
- Self-assembled percolated networks play an important role in many advanced electronic materials and devices. In nanocarbon composites, decreasing the percolation threshold phi(c) is of paramount importance to reduce nanotube bundling, minimize material resources and costs, and enhance charge transport. Here we demonstrate that three-dimensional nanoconfinement in single-wall carbon nanotube/polymer nanocomposites produces a strong reduction in phi(c) reaching the lowest value ever reported in this system of phi(c) approximate to 1.8 X 10(-5) wt % and 4-5 orders of magnitude lower than the theoretical statistical percolation threshold oh phi(stat) Moreover, a change in network resistivity and electrical conduction was observed with increased confinement, and a simple resistive model is used to accurately estimate the difference in is in the confined networks. These results are explained in terms of networks' size, confinement, and tube orientation as determined by atomic force microscopy, electrical conductivity measurements, and polarized Raman spectroscopy. Our findings provide important insight into nanoscale percolated networks and should find application in electronic nanocomposites and devices.
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| 8. |
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| 9. |
- Barzegar, Hamid Reza, et al.
(author)
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Self-assembled PCBM nanosheets : a facile route to electronic layer-on-Layer heterostructures
- 2018
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In: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:2, s. 1442-1447
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Journal article (peer-reviewed)abstract
- We report on the self-assembly of semicrystalline [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanosheets at the interface between a hydrophobic solvent and water, and utilize this opportunity for the realization of electronically active organic/organic molecular heterostructures. The self-assembled PCBM nanosheets can feature a lateral size of >1 cm2 and be transferred from the water surface to both hydrophobic and hydrophilic surfaces using facile transfer techniques. We employ a transferred single PCBM nanosheet as the active material in a field-effect transistor (FET) and verify semiconductor function by a measured electron mobility of 1.2 × 10–2 cm2 V–1 s–1 and an on–off ratio of ∼1 × 104. We further fabricate a planar organic/organic heterostructure with the p-type organic semiconductor poly(3-hexylthiophene-2,5-diyl) as the bottom layer and the n-type PCBM nanosheet as the top layer and demonstrate ambipolar FET operation with an electron mobility of 8.7 × 10–4 cm2 V–1 s–1 and a hole mobility of 3.1 × 10–4 cm2V–1 s–1.
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| 10. |
- Boulanger, Nicolas, et al.
(author)
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Aramid based slot liners for low voltage electric motor applications
- 2024
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In: 2024 IEEE Electrical Insulation Conference (EIC). - : IEEE. - 9798350360431 - 9798350360448 ; , s. 17-21
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Conference paper (peer-reviewed)abstract
- The insulation in the stator of a low voltage electric motor has a double purpose: ensuring the electric insulation around the stator wiring as well as permitting a good evacuation of the generated heat. Improving the heat transfer properties of the slot liner within the stator while maintaining its electrical insulation properties allows for more efficient electric motors. This paper presents different types of composites based on an aramid matrix with boron nitride, zinc oxide and aluminum oxide fillers. The effect of the different filler materials on the thermal conductivity and the electric insulation properties of the slot liner are presented. Perspectives on the needs for a life cycle assessment of the slot liner constituents are evoked.
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| 11. |
- Boulanger, Nicolas, 1986-
(author)
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Carbon nanotubes and graphene polymer composites for opto-electronic applications
- 2016
-
Doctoral thesis (other academic/artistic)abstract
- Carbon nanotubes are carbon based structures with outstanding electronical and mechanical properties. They are used in a wide range of applications, usually embedded in polymer in the form of composites, in order to affect the electronic behavior of the matrix material. However, as the nanotubes properties are directly dependent on their intrinsic structure, it is necessary to select specific nanotubes depending on the application, which can be a complicated and inefficient process. This makes it attractive to be able to reduce the amount of material used in the composites.In this thesis, focus is placed on the electrical properties of the composites. A simple patterning method is presented which allows the use of extremely low amounts of nanotubes in order to increase the electrical conductivity of diverse polymers such as polystyrene (PS) or poly(3-hexylthiophene) (P3HT). This method is called nanoimprint lithography and uses a flexible mold in order to pattern composite films, leading to the creation of conducting nanotube networks, resulting in vertically conducting samples (from the bottom of the film to the top of the imprinted patterns).In parallel, X-ray diffraction measurements have been conducted on thin P3HT polymer films. These were prepared on either silicon substrate or on graphene, and the influence of the processing conditions as well as of the substrate on the crystallinity of the polymer have been investigated. The knowledge of the crystalline structure of P3HT is of great importance as it influences its electronic properties. Establishing a link between the processing conditions and the resulting crystallinity is therefore vital in order to be able to make opto-electronic devices such as transistor or photovoltaic cells.
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| 12. |
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| 13. |
- Boulanger, Nicolas, et al.
(author)
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Enhanced Sorption of Radionuclides by Defect-Rich Graphene Oxide
- 2020
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:40, s. 45122-45135
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Journal article (peer-reviewed)abstract
- Extremely defect graphene oxide (dGO) is proposed as an advanced sorbent for treatment of radioactive waste and contaminated natural waters. dGO prepared using a modified Hummers oxidation procedure, starting from reduced graphene oxide (rGO) as a precursor, shows significantly higher sorption of U(VI), Am(III), and Eu(III) than standard graphene oxides (GOs). Earlier studies revealed the mechanism of radionuclide sorption related to defects in GO sheets. Therefore, explosive thermal exfoliation of graphite oxide was used to prepare rGO with a large number of defects and holes. Defects and holes are additionally introduced by Hummers oxidation of rGO, thus providing an extremely defect-rich material. Analysis of characterization by XPS, TGA, and FTIR shows that dGO oxygen functionalization is predominantly related to defects, such as flake edges and edge atoms of holes, whereas standard GO exhibits oxygen functional groups mostly on the planar surface. The high abundance of defects in dGO results in a 15-fold increase in sorption capacity of U(VI) compared to that in standard Hummers GO. The improved sorption capacity of dGO is related to abundant carboxylic group attached hole edge atoms of GO flakes as revealed by synchrotron-based extended X-ray absorption fine structure (EXAFS) and high-energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) spectroscopy.
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| 14. |
- Boulanger, Nicolas, et al.
(author)
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Graphene induced electrical percolation enables more efficient charge transport at a hybrid organic semiconductor/graphene interface
- 2018
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 20:6, s. 4422-4428
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Journal article (peer-reviewed)abstract
- Self-assembly of semiconducting polymer chains during crystallization from a liquid or melt dictates to a large degree the electronic properties of the resulting solid film. However, it is still unclear how charge transport pathways are created during crystallization. Here, we performed complementary in situ electrical measurements and synchrotron grazing incidence X-ray diffraction (GIXD), during slow cooling from the melt of highly regio-regular poly(3-hexylthiophene) (P3HT) films deposited on both graphene and on silicon. Two different charge transport mechanisms were identified, and were correlated to the difference in crystallites' orientations and overall amount of crystallites in the films on each surface as molecular self-assembly proceeded. On silicon, a weak charge transport was enabled as soon as the first edge-on lamellae formed, and further increased with the higher amount of crystallites (predominantly edge-on and randomly oriented lamellae) during cooling. On graphene however, the current remained low until a minimum amount of crystallites was reached, at which point interconnection of conducting units (face-on, randomly oriented lamellae and tie-chains) formed percolated conducting pathways across the film. This lead to a sudden rapid increase in current by approximate to 10 fold, and strongly enhanced charge transport, despite a much lower amount of crystallites than on silicon.
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| 15. |
- Boulanger, Nicolas, et al.
(author)
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High Surface Area "3D Graphene Oxide" for Enhanced Sorption of Radionuclides
- 2022
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In: Advanced Materials Interfaces. - : John Wiley & Sons. - 2196-7350. ; 9:18
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Journal article (peer-reviewed)abstract
- Here preparation of high surface area activated reduced graphene oxide (arGO) oxidized into a 3D analogue of defect-rich GO (dGO) is reported. Surface oxidation of arGO results in carbon to oxygen ratio C/O = 3.3, similar to the oxidation state of graphene oxide while preserving high BET surface area of about 880 m2 g−1. Analysis of surface oxidized arGO shows high abundance of oxygen functional groups which converts hydrophobic precursor into hydrophilic material. High surface area carbons provide the whole surface for oxidation without the need of intercalation and lattice expansion. Therefore, surface oxidation methods are sufficient to convert the materials into 3D architectures with chemical properties similar to graphene oxide. The "3D graphene oxide" shows high sorption capacity for U(VI) removal in an extraordinary broad interval of pH. Notably, the surface oxidized carbon material has a rigid 3D structure with micropores accessible for penetration of radionuclide ions. Therefore, the bulk "3D GO" can be used as a sorbent directly without dispersing, the step required for GO to make its surface area accessible for pollutants.
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| 16. |
- Boulanger, Nicolas, et al.
(author)
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High surface area activated carbon prepared from wood-based spent mushroom substrate for supercapacitors and water treatment
- 2024
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In: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 680
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Journal article (peer-reviewed)abstract
- Edible white-rot fungi are commonly cultivated on wood-based substrates and selectively degrade lignin to a larger extent during their growth. Spent mushroom substrate (SMS) is produced in huge amounts by the mushroom industry and today there is a lack of proven methods to valorize this kind of biomass waste, which in most cases is landfilled or used as fuel. This study demonstrates that birch wood-based SMS from the cultivation of oyster mushrooms can be converted into high-quality activated carbon (AC) with an extremely high surface area of about 3000 m2/g. These activated carbons showed good performance when used in electrodes for supercapacitors, with energy storage parameters nearly identical to AC produced from high-quality virgin birch wood. Moreover, AC produced from SMS showed high potential as an adsorbent for cleaning reactive orange-16 azo dye from aqueous solutions as well as contaminants from synthetic effluents and from real sewage water. The kinetics of adsorption were well represented by the Avrami fractional order model and isotherms of adsorption by the Liu model. The theoretical maximum reactive orange-16 adsorption capacities were approximately 519 mg/g (SMS-based carbon) and 553 mg/g (virgin birch-based carbon). The removal of contaminants from synthetic effluents made of different dyes and inorganic compounds was around 95% and 83% depending on the effluent composition. The removal of contaminants from raw sewage water was around 84%, and from treated sewage water was around 68%. Overall, the results showed that activated carbon prepared from waste generated during cultivation of white-rot fungi is as good as activated carbon prepared from high-quality virgin wood.
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| 17. |
- Boulanger, Nicolas, et al.
(author)
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In situ probing of the crystallization kinetics of rr-P3HT on single layer graphene as a function of temperature
- 2017
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:12, s. 8496-8503
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Journal article (peer-reviewed)abstract
- We studied the molecular packing and crystallization of a highly regio-regular semiconducting polymer poly(3-hexylthiophene) (P3HT) on both single layer graphene and silicon as a function of temperature, during cooling from the melt. The onset of crystallization, crystallites' size, orientation, and kinetics of formation were measured in situ by synchrotron grazing incidence X-ray diffraction (GIXD) during cooling and revealed a very different crystallization process on each surface. A favored crystalline orientation with out of plane pi-pi stacking formed at a temperature of 200 degrees C on graphene, whereas the first crystallites formed with an edge-on orientation at 185 degrees C on silicon. The crystallization of face-on lamellae revealed two surprising effects during cooling: (a) a constant low value of the pi-pi spacing below 60 degrees C; and (b) a reduction by half in the coherence length of face-on lamellae from 100 to 30 degrees C, which corresponded with the weakening of the 2nd or 3rd order of the in-plane (k00) diffraction peak. The final ratio of face-on to edge-on orientations was 40% on graphene, and 2% on silicon, revealing the very different crystallization mechanisms. These results provide a better understanding of how surfaces with different chemistries and intermolecular interactions with the polythiophene polymer chains lead to different crystallization processes and crystallites orientations for specific electronic applications.
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| 18. |
- Boulanger, Nicolas, et al.
(author)
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Nano-engineered Nanotube Networks for Enhanced Vertical Charge Transport at Ultralow Nanotube Loading in a P3HT Nanocomposite Film
- 2014
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Conference paper (peer-reviewed)abstract
- Due to their exceptional charge transport properties, single wall carbon nanotubes (SWNTs) are expected to enhance the performance of organic based photovoltaic (PV) solar cells through an ultrafast charge transfer process when placed in contact with a semiconducting organic interface such as poly-3-hexylthiophene (P3HT)1. However, in order to produce efficient charge transport through the active layer, a percolated network of interconnected tubes must be formed. Typical methods (e.g. spin-coating, drop-casting) do not form an efficient pathway for charges, and they often result in randomly organized networks and nanotube aggregates which have been shown to lower conductivity2,3. Here, we present a new concept where nanoscale nano-engineered SWNT networks are formed in a composite film made of >90% semi-conducting nanotubes in a P3HT matrix.4 These nanoscale networks result in several orders of magnitude increase in charge transport through the composite layer made of P3HT, and compared to an identical composite film simply spun or drop-cast. These nano-networks also result in a strong effective decrease of the percolation threshold, thereby offering the possibility to use much lower amounts of nanotubes in devices. We discuss these results and the mechanisms of charge transport enhancement.Stranks, S. D. ; Weisspfennig, C.; Parkinson, P.; Johnston, M. B. ; Herz, L. M. ; Nicholas, R. J. Nano Lett. 2011, 11(1), 66–72.Nirmalraj, P. N. ; Lyons, P. E. ; Coleman, J. N. ; Boland, J. J. Nano Lett. 2009, 9(11), 3890–3895.Kymakis, E.; Amaratunga, G. A. J. J. Appl. Phys. 2006, 99 (8), 084302.Barbero, D. R. ; Boulanger, N.; Ramstedt; M., Yu, J. , Advanced Materials 2014, 21, 3111.
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| 19. |
- Boulanger, Nicolas, et al.
(author)
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Nanostructured networks of single wall carbon nanotubes for highly transparent, conductive, and anti-reflective flexible electrodes
- 2013
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:2
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Journal article (peer-reviewed)abstract
- Highly transparent, anti-reflective, flexible, and conductive electrodes are produced by nanopatterning of a polymer composite made of single wall carbon nanotubes (SWNTs). The formation of nanostructures creates interconnected nanotubes and vertically aligned SWNT networks which greatly improves charge transport compared to a traditionally mixed composite. These electrodes moreover possess high transparency (98% at 550 nm) and good anti-reflective properties. The use of low nanotube loadings provides an economical solution to make conductive and highly transparent flexible electrodes. The process used is simple and can be easily scaled to large areas by roll to roll processes.
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| 20. |
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| 21. |
- Boulanger, Nicolas, et al.
(author)
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Spray deposition of supercapacitor electrodes using environmentally friendly aqueous activated graphene and activated carbon dispersions for industrial implementation
- 2021
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In: ChemElectroChem. - : John Wiley & Sons. - 2196-0216. ; 8:7, s. 1349-1361
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Journal article (peer-reviewed)abstract
- A spray gun machine was used to deposit high‐surface‐area supercapacitor electrodes using green non‐toxic aqueous dispersions based on different kinds of high specific surface area nanostructured carbon materials: activated graphene (a‐rGO) and activated carbon (AC). Tuning the spray conditions and dispersion formulation allowed us to achieve good adhesion to stainless‐steel current collectors in combination with high surface area and a satisfactory mechanical stability of the electrodes. The specific surface area of approximately 2000 m2/g was measured directly on a‐rGO and AC electrodes showing only around a 20 % decrease compared to the precursor powder materials. The performance of the electrodes deposited on stainless‐steel and aluminum current collectors was tested in supercapacitor devices using three electrolytes. The electrodes were tested in an “as‐deposited” state and after post‐deposition annealing at 200 °C. The spray deposition method and post‐deposition annealing are completely compatible with roll‐to‐roll industrial production methods. The a‐rGO demonstrated superior performance compared to AC in supercapacitor electrodes with gravimetric capacitance, energy, and power density parameters, which exceed commercially available analogues. The formulation of the dispersions used in this study is environmentally friendly, as it is based on only on water as a solvent and commercially available non‐toxic additives (graphene oxide, fumed silica, and carbon nanotubes).
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| 22. |
- Boulanger, Nicolas, et al.
(author)
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Super-oxidized “activated graphene” as 3D analogue of defect graphene oxide : oxidation degree vs U(VI) sorption
- 2023
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In: Journal of Hazardous Materials. - : Elsevier. - 0304-3894 .- 1873-3336. ; 457
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Journal article (peer-reviewed)abstract
- Porous carbons are not favorable for sorption of heavy metals and radionuclides due to absence of suitable binding sites. In this study we explored the limits for surface oxidation of “activated graphene” (AG), porous carbon material with the specific surface area of ∼2700 m2/g produced by activation of reduced graphene oxide (GO). Set of “Super-Oxidized Activated Graphene” (SOAG) materials with high abundance of carboxylic groups on the surface were produced using “soft” oxidation. High degree of oxidation comparable to standard GO (C/O=2.3) was achieved while keeping 3D porous structure with specific surface area of ∼700–800 m2/. The decrease in surface area is related to the oxidation-driven collapse of mesopores while micropores showed higher stability. The increase in the oxidation degree of SOAG is found to result in progressively higher sorption of U(VI), mostly related to the increase in abundance of carboxylic groups. The SOAG demonstrated extraordinarily high sorption of U(VI) with the maximal capacity up to 5400 μmol/g, that is 8.4 – fold increase compared to non-oxidized precursor AG, ∼50 –fold increase compared to standard graphene oxide and twice higher than extremely defect-rich graphene oxide. The trends revealed here show a way to further increase sorption if similar oxidation degree is achieved with smaller sacrifice of surface area.
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| 23. |
- Boulanger, Nicolas, et al.
(author)
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SWNT nano-engineered networks strongly increase charge transport in P3HT
- 2014
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In: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 6:20, s. 11633-11636
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Journal article (peer-reviewed)abstract
- We demonstrate the formation of arrays of 3D nano- sized networks of interconnected single-wall carbon nanotubes (SWNT) with well defined dimensions in a poly-3- hexylthiophene (P3HT) thin film. These novel nanotube nano-networks produce efficient ohmic charge transport, even at very low nanotube loadings and low voltages. An increase in conductivity between one and two orders of magnitude is observed compared to a random network. The formation of these nano-engineered networks is compatible with large area imprinting and roll to roll processes, which makes it highly desirable for opto-electronic and energy conversion applications using carbon nanotubes.
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| 24. |
- Das, Lakshmi, et al.
(author)
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NiO thin films fabricated using spray-pyrolysis technique : structural and optical characterization and ultrafast charge dynamics studies
- 2024
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In: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 57:38
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Journal article (peer-reviewed)abstract
- Nickel (II) oxide, NiO, is a wide band gap Mott insulator characterized by strong Coulomb repulsion between d-electrons and displays antiferromagnetic order at room temperature. NiO has gained attention in recent years as a very promising candidate for applications in a broad set of areas, including chemistry and metallurgy to spintronics and energy harvesting. Here, we report on the fabrication of polycrystalline NiO using spray-pyrolysis technique, which is a deposition technique able to produce quite uniform films of pure and crystalline materials without the need of high vacuum or inert atmospheres. The composition and structure of the NiO thin films were then studied using x-ray diffraction, and atomic force and scanning electron microscopies (SEM). The phononic and magnonic properties of the NiO thin films were also studied via Raman spectroscopy, and the ultrafast electron dynamics by using optical pump probe spectroscopy. We found that the NiO samples display the same phonon and magnon excitations expected for single crystal NiO at room temperature, and that electron dynamics in our system is like those of previously reported NiO mono- and polycrystalline systems synthesized using different techniques. These results prove that spray-pyrolysis can be used as affordable and large-scale fabrication technique to synthesize strongly correlated materials for a large set of applications.
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| 25. |
- Ekspong, Joakim, et al.
(author)
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Surface activation of graphene nanoribbons for oxygen reduction reaction by nitrogen doping and defect engineering : An ab initio study
- 2018
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In: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 137, s. 349-357
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Journal article (peer-reviewed)abstract
- Introducing heteroatoms and creating structural defects on graphene is a common and rather successful strategy to transform its inert basal plane into an efficient metal-free electrocatalyst for oxygen reduction reaction (ORR). However, the intricate atomic configuration of defective graphenes difficult their optimization as ORR electrocatalysts, where not only a large density of active sites is desirable, but also excellent electrical conductivity is required. Therefore, we used density functional theory to investigate the current-voltage characteristics and the catalytic active sites towards ORR of nitrogen-doped and defective graphene by using 8 zig-zag graphene nanoribbons as model systems. Detailed ORR catalytic activity maps are created for ten different systems showing the distribution of catalytic hot spots generated by each defect. Subsequently, the use of both current-voltage characteristics and catalytic activity maps allow to exclude inefficient systems that exhibit either low electrical conductivity or have adsorption energies far from optimal. Our study highlights the importance of considering not only the interaction energy of reaction intermediates to design electrocatalysts, but also the electrical conductivity of such configurations. We believe that this work is important for future experimental studies by providing insights on the use of graphene as a catalyst towards the ORR reaction.
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