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Hydrogen Electrode (hydrogen + electrode)
Selected AbstractsControlling Photoactivity in Ultrathin Hematite Films for Solar Water-SplittingADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Florian Le Formal Abstract A promising route to increase the performance of hematite (,-Fe2O3) photoelectrodes for solar hydrogen production through water-splitting is to use an extremely thin layer of this visible light absorber on a nanostructured scaffold. However, the typically poor performance of ultrathin (ca. 20,nm) films of hematite has been the limiting factor in implementing this approach. Here, the surprising effect of a substrate pretreatment using tetraethoxysilicate (TEOS) is reported; it results in drastic improvements in the photoperformance of 12.5,nm thick films of hematite. These films exhibit a water oxidation photocurrent onset potential at 1.1,V versus the reversible hydrogen electrode (vs. RHE) and a plateau current of 0.63,mA cm,2 at 1.5,V vs. RHE under standard illumination conditions, representing the highest reported performance for ultrathin hematite films. In contrast, almost no photoactivity is observed for the photoanode with the same amount of hematite on an untreated substrate. A detailed study of the effects of the TEOS treatment shows that a monolayer of SiOx is formed, which acts to change the hematite nucleation and growth mechanism, increases its crystallinity, reduces the concentration of carrier trapping states of the ultrathin films, and suggests its further application to quantum-dot and extremely-thin-absorber (ETA)-type solar cells. [source] Combinatorial Search for Quaternary Methanol Tolerant Oxygen Electro-Reduction CatalystFUEL CELLS, Issue 1 2010M. K. Jeon Abstract A combinatorial library containing 645 different compositions was synthesised and characterised for methanol tolerant oxygen electro-reduction reaction (ORR) catalytic performance. The library was composed of compositions involving between 1 and 4 metals among Pt, Ru, Fe, Mo and Se. In an optical screening test, Pt(50)Ru(10)Fe(20)Se(10) composition exhibited the highest ORR activity in the presence of methanol. This composition was further investigated by synthesis and characterisation of a powder version catalyst [Pt(50)Ru(10)Fe(20)Se(10)/C]. At 0.85,V [vs. reversible hydrogen electrode (RHE)] in the absence of methanol, the Pt/C catalyst exhibited higher ORR current (0.0990,mA) than the Pt(50)Ru(10)Fe(20)Se(10)/C catalyst (0.0902,mA). But much higher specific activity (12.7 ,A cmpt,2) was observed in the Pt(50)Ru(10)Fe(20)Se(10)/C catalyst than for the Pt/C catalyst 6.51 ,A cmpt,2). In the presence of methanol, the ORR current decreased by 0.0343 and 0.247,mA for the Pt(50)Ru(10)Fe(20)Se(10)/C and Pt/C catalysts, respectively, which proved the excellent methanol tolerance of the Pt(50)Ru(10)Fe(20)Se(10)/C catalyst. [source] Intelligent structure design of membrane cathode assembly for direct methanol fuel cellINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2005K. Furukawa Abstract The performance and the structural model of membrane electrode assembly (MEA) have been developed and experimentally verified with fundamental calculations of the direct methanol fuel cell (DMFC). The model provides information concerning the influence of the operating and structural parameters. The composition and performance optimization of MEA structure in DMFC has been investigated by including both electrochemical reaction and mass transport process. In the experimentation, the effect of Nafion content and loading method in the catalyst layer of cathode for DMFC was investigated. For the spray method electrode (SME), the cell performance and cathode performance using a dynamic hydrogen electrode (DHE) as a reference electrode was improved in comparison with those of the PME electrode by decreasing cathode potential. From ac impedance measurements of the cathode, the adsorption resistance of the SME electrode was decreased compared with that of the PME electrode. The higher cell performance was mostly dependent on the adsorption resistance. In the modelling, the cathode overpotential was decreased with increasing ionomer content, due to increasing ionic conductivity for proton transfer and the larger reaction site. The resistance to oxygen transport was increased at the same time, and became dominant at higher ionomer loadings, leading to an increase in the voltage loss. The ratio of ionomer to void space in the cathode affected the cathode polarization, which had the lowest resistance of oxygen diffusion at the ratio of 0.1,0.2. Copyright © 2005 John Wiley & Sons, Ltd. [source] Evaluation of applied cathode potential to enhance biocathode in microbial fuel cellsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2009Peng Liang Abstract BACKGROUND: The biocathode is proving to be a promising feature for development of the microbial fuel cell (MFC), although much work remains to be done to increase its power generation. This study aimed to enhance the performance of a biocathode by applying selected cathode potential. RESULTS: When five two-chambered MFCs were operated at selected cathode potentials of 142, 242, 342, 442, or 542 mV (vs standard hydrogen electrode), those MFCs with selected potentials lower than 342 mV could start up, and the highest power density of 0.11 W m,3 was obtained at a selected potential of 242 mV. An inner-biocathode MFC was then constructed and operated at a start-up cathode potential of 242 mV for 30 days. The open circuit cathode potential increased from 477 ± 9 mV to 572 ± 8 mV compared with the potential of the initially abiotic cathode, resulting in an increase in the maximum power density (4.25 ± 0.16 W m,3) of 106%. In addition, tests of continuous operation showed that a loading rate of 135 mg COD L,1 d,1 was optimal for obtaining maximum power generation in the system developed for this study. CONCLUSION: The results indicated that an optimal cathode potential of 242 mV enhanced the performance of a biocathode using oxygen as the electron acceptor. Copyright © 2009 Society of Chemical Industry [source] Anodic oxides on a beta type Nb,Ti alloy and their characterization by electrochemical impedance spectroscopyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2010Michael Teka Woldemedhin Abstract Anodic oxides were grown on the surface of an electropolished (Ti,30,at% Nb) beta-titanium (,-Ti) alloy by cyclic voltammetry. The scan rate was 100,mV,s,1 between 0 and 8,V in increments of l,V in an acetate buffer of pH 6.0. Electrochemical impedance spectroscopy was carried out right after each anodic oxide growth increment to study the electronic properties of the oxide/electrolyte interface in a wide frequency range from 100,kHz to 10,MHz with an AC perturbation voltage of 10,mV. A film formation factor of 2.4,nm,V,1 was found and a relative permittivity number (dielectric constant) of 42.4 was determined for the oxide film formed. Mott,Schottky analysis on a potentiostatically formed 7,nm thick oxide film was performed to assess the semiconducting properties of the mixed anodic oxide grown on the alloy. A flat band potential of ,0.47,V (standard hydrogen electrode, SHE) was determined, connected to a donor density of 8.2,×,1017,cm,3. ,-Ti being highly isotropic in terms of mechanical properties should be superior to the stiffer ,-Ti compound. Its application, however, requires a passivation behaviour comparable or better than ,-Ti which in fact is found. [source] | ||||||||||