Electrocatalytic activity of Pt alloys with Ni, Co, and Fe, formed by sputtering, was investigated with regard to the oxygen reduction reaction (ORR) in perchloric acid solution. Hydrodynamic voltammograms with rotated electrodes were used to measure the electrocatalytic activity. Maximum activity was observed at ca. 30, 40, and 50% content of Ni, Co, and Fe, respectively, by which 10, 15, and 20 times larger kinetic current densities than that of pure Pt were attained. X‐ray photoelectron spectroscopy analysis of the surfaces after the reaction indicated that the active surfaces were covered by a few monolayers of Pt. We present an enhancing mechanism for the ORR based on an increased d‐electron vacancy of the thin Pt surface layer caused by underlying alloy. Results of this work contribute in development of new active cathode catalysts for fuel cells used as power sources of electric vehicles, etc. © 1999 The Electrochemical Society. All rights reserved.

Polymer electrolyte fuel cells have attracted enormous interest as a primary power source for electric vehicles. Water management in the electrolyte is one of the complicated problems to be overcome. A new self‐humidifying electrolyte membrane is proposed to solve this problem. Self‐humidification allows the use of very thin membranes, simultaneously allowing high performance of the cell. Use of the new, thin membranes makes the system very simple and ready for cold starts and also amenable to abrupt load changes. The electrolyte is comprised of 50 μm thick Nafion membrane containing 0.07 mg/cm² of platinum catalyst particles (d = 1 to 2 nm) and a few weight percent of a hygroscopic material such as silica or titania (d = ca. 5 to 7 nm) . The platinum particles catalyze the oxidation of crossover hydrogen with oxygen to generate water, which in turn is adsorbed by the oxide particles. The cell shows exceptionally stable and high performance even under ambient pressure conditions when operated with hydrogen saturated with water at 20°C and dry oxygen. The internal resistance was measured to be 0.06 Ω cm², and the output of the cell was 0.63 W/cm² i.e., 0.9 A/cm² at 0.7 V with an energy efficiency of 60%. The output was 1 W/cm² in the voltage region of 0.6 to 0.4 V yielding current densities of 1.6 to 2.5 A/cm². Hydrogen depleted for self‐humidification was estimated to be less than a few percent under these operating conditions.

The electrocatalytic activity for H₂ oxidation in the presence of 100 ppm CO has been investigated on a series of binary Pt alloy electrocatalysts with non-precious metals of various compositions. Regardless of the composition, Pt–Fe, Pt–Ni, Pt–Co and Pt–Mo alloys have been found to exhibit excellent CO tolerance in H₂ oxidation, similar to that of the Pt–Ru alloy. At these CO-tolerant electrodes, the equilibrium coverage of CO was suppressed to values less than ca. 0.6. Based on X-ray photoelectron spectroscopy (XPS) data, it was found that the surfaces of all non-precious metal alloys are composed of a thin Pt layer with an electronic structure different from that of pure Pt, indicating an increased 5d vacancy of Pt in the layers of the CO-tolerant alloys. The CO coverage, particularly with multi-bonding, was lowered due to decreased electron donation from the Pt band to the 2π* orbital of CO. A weakening of bond strength between the Pt skin layer and CO was also indicated by in situ FTIR, suggesting that the H₂ oxidation sites are not blocked by CO due to its enhanced mobility. Thus, the mechanism of CO tolerance described above at the Pt skin on alloy surfaces is proposed as a “detoxification mechanism”.