ABSTRACT
Correction for 'Effects of p-substituents on electrochemical CO oxidation by Rh porphyrin-based catalysts' by Shin-ichi Yamazaki et al., Phys. Chem. Chem. Phys., 2010, 12, 8968-8976.
ABSTRACT
A Rh porphyrin on carbon black was shown to catalyze the electro-oxidation of several aliphatic alcohols (ethanol, 1-propanol, and 2-propanol) and benzyl alcohols. The overpotentials for alcohol oxidation were very low. The reaction mechanism and substrate specificity are discussed.
ABSTRACT
Electrochemical CO oxidation by several carbon-supported rhodium tetraphenylporphyrins with systematically varied meso-substituents was investigated. A quantitative analysis revealed that the p-substituents on the meso-phenyl groups significantly affected CO oxidation activity. The electrocatalytic reaction was characterized in detail based on the spectroscopic and X-ray structural results as well as electrochemical analyses. The difference in the activity among Rh porphyrins is discussed in terms of the properties of p-substituents along with a proposed reaction mechanism. Rhodium tetrakis(4-carboxyphenyl)porphyrin (Rh(TCPP)), which exhibited the highest activity among the porphyrins tested, oxidized CO at a high rate at much lower potentials (<0.1 V vs. a reversible hydrogen electrode, at 60 degrees C) than the present PtRu catalysts. This means that CO is electrochemically oxidized by this catalyst when a slight overpotential is applied during the operation of a proton exchange membrane fuel cell. This catalyst exhibited little H(2) oxidation activity, in contrast to Pt-based catalysts.
ABSTRACT
Nano-submicron particles of sub-stoichiometric titanium oxide (TiOx) were synthesized by irradiation of TiO(2) particles dispersed in liquid with a Nd:YAG pulsed UV laser, and their physicochemical and electrochemical properties were examined. After laser irradiation for 1 h, spherical oxide particles of up to ca. 300 nm in diameter were formed regardless of the liquid used, however the reduction of TiO(2) largely depended on the liquid: acetonitrile most strongly promoted the reduction of TiO(2) by UV laser irradiation. The mean valence of titanium in TiOx synthesized in acetonitrile was ca. 3.5, which is comparable to that of the most-reduced Magnéli phase, Ti(4)O(7). While the electrical conductivity of as-washed TiOx was significantly low, annealing at 900 degrees C in hydrogen dramatically improved conductivity. The oxidation resistance of TiOx was examined by cyclic voltammetry to a high potential (1.5 V) using a MEA under PEMFC operating conditions. TiOx showed a much lower anodic corrosion current at >1.0 V than XC-72R carbon, which suggests that TiOx may exhibit superior oxidation resistance as a catalyst support material at high potentials.
ABSTRACT
In this communication, we demonstrate that certain kinds of Rh porphyrins on carbon black can electrochemically oxidize aldose at low potentials. The onset potential was much lower than those with the other complex-based catalysts. A product analysis suggested that this reaction involves 2-electron oxidation of the aldehyde group.
Subject(s)
Carbohydrates/chemistry , Metalloporphyrins/chemistry , Rhodium/chemistry , Aldehydes/chemistry , Catalysis , Electrochemistry , Electrons , Molecular Structure , Oxidation-Reduction , StereoisomerismABSTRACT
The behavior of platinum dissolution and deposition in the polymer electrolyte membrane of a membrane-electrode-assembly (MEA) for a proton-exchange membrane fuel cell (PEMFC) was studied using potential cycling experiment and high-resolution transmission electron microscopy (HRTEM). The electrochemically active surface area decreased depending on the cycle number and the upper potential limit. Platinum deposition was observed in the polymer electrolyte membrane near a cathode catalyst layer. Platinum deposition was accelerated by the presence of hydrogen transported through the membrane from an anode compartment. Platinum was transported across the membrane and deposited on the anode layer in the absence of hydrogen in the anode compartment. This deposition was also affected by the presence of oxygen in the cathode compartment.
Subject(s)
Electric Power Supplies , Electrolytes/chemistry , Membranes, Artificial , Platinum/chemistry , Polymers/chemistry , Chemical Phenomena , Chemistry, Physical , Hydrogen/chemistry , Microscopy, Electron, Transmission/instrumentation , Microscopy, Electron, Transmission/methods , Oxygen/chemistry , Particle Size , Sensitivity and Specificity , Surface PropertiesABSTRACT
We have found efficient electrocatalytic removal of CO by rhodium octaethylporphyrin on carbon black at a wide potential range. Using carbon-supported rhodium octaethylporphyrin, we have separated the Rh(II) state participating reaction and the Rh(III) state participating reaction with CO. We have clearly demonstrated electrocatalytic CO oxidation by rhodium(III) porphyrin. The onset potential for CO oxidation is much lower than that for CO oxidation by conventional Pt/Ru catalysts and cobalt porphyrin.
Subject(s)
Carbon Monoxide/chemistry , Carbon/chemistry , Porphyrins/chemistry , Rhodium/chemistry , Adsorption , ElectrochemistryABSTRACT
We have clearly demonstrated reversible cyclic voltammograms for the redox reaction between the Rh(II) and Rh(III) states in rhodium octaethylporphyrin [Rh(OEP)] adsorbed on carbon black in an acidic aqueous solution. The emergence of the reversible wave can be ascribed to the suppression of the undesirable reactions between two molecules of [Rh(II)(OEP)] because of its strong interaction with the carbon black. The generated [Rh(II)(OEP)] exhibits a potent catalytic O(2) reduction activity.
