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Platinum nanoparticle-supported boron-doped diamond powder (Pt/BDDP) was prepared and investigated as a durable polymer electrolyte fuel cell (PEFC) cathode catalyst. The use of the nanocapsule method enabled dense deposition of Pt nanoparticles (2–5 nm in size) on a boron-doped diamond (BDD) powder

Cobalt polypyrrole-supported carbon (CoPPy/C) has been expected to be a low-cost alternative to platinum catalysts for proton exchange membrane fuel cell (PEMFC) cathode. Although the catalytic activity of the CoPPy/C is relatively high, improvement of the durability to long-term use is still challenging problem. In order to know the deterioration mechanism of PEMFC cathode, dynamic-secondary ion mass spectrometry (D-SIMS) was used in this study for analysis of cathode catalyst layer/solid electrolyte membrane interfaces before and after an aging test. The depth profile of cobalt species across the interface of a CoPPy/C cathode was significantly changed after the aging test. From the depth profile of cobalt in the CoPPy/C catalyst, it is suggested that the cobalt species may transfer in the membrane along with the flow of the back diffusion water.

Electropolymerized cobalt salen compounds on pyrolytic graphite electrodes were first tested as oxygen reduction catalysts in aqueous solutions of various pH. N,N'‐Bis(salicylidene)ethylenediaminocobalt(II) [abbreviated Co(salen)] and its analogs were polymerized on a basal plane of pyrolytic graphite electrode by electrochemical polarization from deaerated acetonitrile solutions. The cyclic voltammetry of Co(salen) modified electrodes showed that electropolymerized Co(salen) effectively catalyzed oxygen reduction in aqueous solutions, and features such as half‐wave potentials or limiting current density of oxygen reduction were satisfactory as compared with those of cobalt porphyrin‐modified electrodes. The characteristics of oxygen reduction catalyzed by electropolymerized Co(salen) were investigated using rotating ring‐disk electrode measurements in acidic, neutral, and basic solutions. The efficiency of four‐electron reduction of oxygen was found to be best in basic solutions. The results revealed that although in acidic media the catalyst performance deteriorated in a short time, the performance in neutral and basic media was relatively good as compared with that of platinum, the best catalyst for this reaction. © 1999 The Electrochemical Society. All rights reserved.

Oxygen reduction characteristics of graphite electrodes modified with aggregated cobalt-porphyrins heat-treated at various temperatures and then impregnated in Nafion polymer were investigated systematically. The aggregated cobalt-porphyrin compound was adsorbed on graphite powder and then heat-treated at various temperatures ranging from 200 through 1200 °C. The catalysts were evaluated for electroreduction performances of oxygen on modified electrodes in sulfuric acid solutions. The electrocatalytic performances of catalysts as measured in rotating ring-disk electrodes showed that the most effective catalytic activity for oxygen reduction was attained for the aggregated cobalt-porphyrin compounds on graphite powder heat-treated at temperatures between 600 and 800 °C. The surface concentration of Co and N as measured by X-ray photoelectron spectroscopy increased as the heat-treatment temperature was increased up to 800 °C. The electrochemical performance of pyrolyzed cobalt-porphyrin catalysts changed in parallel with the surface concentration of Co and N. In the temperature range 600-800 °C, it appeared that the increased catalytic activity originated from the well-dispersed Co-N 4 moiety or from fragments of the original molecules still retaining the cobalt bound to nitrogen atoms. In the higher temperature region, Co-N 4 bonds were no longer detected, and the presence of cobalt in the metallic states (β-Co) in the catalysts was confirmed by X-ray diffraction analysis. From the results of the stability tests, the pyrolyzed cobalt porphyrin electrode systems were found to be more stable than the nonheat-treated catalysts.

The effect of contamination by Ca{sup 2+} ions in proton conductive membranes for polymer electrolyte fuel cells was investigated systematically. Ion and water transport characteristics of Nafion membranes, which were equilibrated with 0.02 to 0.03 kmol/m{sup 3} of HCl/CaCl{sub 2} mixed solutions of various mixing ratios, were studied by electromotive force analysis. Membrane composition analysis, showed that Ca{sup 2+} has much higher affinity than H{sup +} to the ion exchange sites in Nafion membranes. The water content in the membrane, as expressed by the amount of water per cationic site H{sub 2}O/SO{sub 3}{sup {minus}}, decreased about 19% from 21 for H-form membrane to 17 for Ca-form membrane. The water transference coefficient was obtained from streaming potential measurements of Nafion 115 membranes of various H{sup +}/Ca{sup 2+} cationic compositions. The water transference coefficient increased from 2.5 toward 11 as the Ca{sup 2+} content in the membrane increased, especially when the equivalent fraction of H{sup +} in the cationic exchange sites x{sub HM} became less than 0.5. Ionic transference numbers for H{sup +} in the membrane, determined by a new electromotive force method, showed rapid decrease when the cationic site occupancy by H{sup +} became less than 0.5. Membrane conductivity changed linearlymore » with H{sup +} composition in the membrane. In strong contrast to the interaction mode between H{sup +} and Ca{sup 2+} cations during ionic conduction, which appeared almost independent, a certain extent of interference was observed among water molecules as they were carried along by cations in the membrane. It was predicted that if Ca{sup 2+} ions enter the fuel-cell membrane, they cause serious effects to membrane drying and result in deterioration of fuel-cell performance. The advantage of this methodology in the study of transport characteristics of fuel-cell membranes is stressed due to ease and accuracy of measurements.« less

Various electrodes modified with cobalt-porphyrin-clay complexes (CoTMPyP- and CoTAPP-Mon, Ver, and AW-Kao), silver colloid (AgCol), and polymers [PVA and P(2VPy)] were synthesized and their electrochemical properties were investigated to evaluate the possibility of creating oxygen sensors. The oxygen reduction based on the two-electron transfer mechanism (Eq. 1) occurred in the cobalt-porphyrin-clay/AgCol/polymer-modified electrode and the peak current density (I P ) depended quantitatively on the concentration of oxygen. As for the evaluation of oxygen sensors in the modified electrode systems at the optimal composition, (i) the I p increased linearly with the concentration of oxygen, (ii) the response was a reversible and rapid one, and (iii) the modified electrodes in the Mon and Ver systems were most stable (lifetime > 6 h under hydrodynamic conditions). The cobalt-porphyrin-clay/AgCol/polymer-modified electrode systems acted effectively as oxygen sensors

The behavior of corrosion inhibition of mild steel by various cationic and anionic polymers, that is, polyethyleneimine (PEI), its derivative (PEID), polyarylamine (PAAm) and polydicyanodiamide derivative (PDCDA) as cationic polymers and polymaleic acid derivative (PMAD), polyacrylic acid derivative (PAAD) and polyacrylic acid (PAA) as anionic polymers, was investigated by corrosion tests and physicochemical measurements. Testing was done in two pseudoconcentrated solutions with low (LC) and high (HC) concentrations of ionic species like Ca 2+ and Cl

Polymer films, based on aniline‐, phenol‐, normal vinyl‐ and heterocyclic/vinyl‐type monomers, were synthesized on mild steel by various electropolymerizations (EPs), and their corrosion resistance and structure were investigated because a new coating system with corrosion resistance for mild steel has been obtained. The relationship between synthetic method, structure, and function (corrosion resistance) for coated mild steel is discussed. In electro‐oxidation polymerization (EOP) incomplete, porous, and thin films were formed on steel surfaces, while in electroreduction polymerization (ERP), complete, more compact, and thicker films were formed on steel surfaces in comparison with EOP films. The most corrosion‐preventive film under this experimental condition was a poly(2‐vinylpyridine) film with an inhibition efficiency (η) of corrosion of about 80–90%. The most effective EP method was a constant potential electrolysis using a two‐electrode cell with an η value of more than 90%. Since the organic layer formed during EP was ionic and the EP of 2‐vinylpyridine (monomer) was promoted, the thick poly(2‐vinylpyridine) film was formed on the steel surface. The results of structural analysis suggest that, (i) poly(2‐vinylpyridine) film, , was formed on the steel surface by EP, (ii) the coated steel was composed of polymer and steel layers, and oxidation products were not present in the interface, and (iii) the solvents in the film were evaporated and the thermal‐polymerization of poly(2‐vinylpyridine) continued with curing.

Corrosion behavior of mild steel in various hydroxy acid solutions of glycolic, lactic, malic, tartaric, and citric acids was investigated by corrosion tests, electrochemical measurements, solution analysis, and new methods of surface analyses

Blood coagulation on the electrode surface is a serious problem for a superoxide anion radical (O2−∙) sensor because it causes deterioration of the current signal especially in vivo. In order to solve this problem, we have developed iron porphyrin-based O2−∙ sensors immobilizing heparin, which is an anti-thrombotic compound, on the surface. In the present study, we immobilized heparin with a polyethylenedioxythiophene (PEDOT) matrix on poly[iron tetrakis(3-thienyl)porphyrin]-modified glassy carbon (GC) electrode, and the stability of the modified sensor to blood coagulation was investigated. The PEDOT matrix was found to be more effective for stable electrochemical detection of O2−∙ after immersion in a fibrinogen/thrombin solution for two weeks, while serious electrode fouling due to blood clot formation was occurred at a sensor using a polypyrrole matrix after immersion in the solution for one week.

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