Studies on the mechanism of the hydrogen electrode reaction by means of deuterium tracer—II. The reaction mechanism

The exchange reaction between deuterium gas and light water was conducted with Ni, Rh, and Pt catalyst. Through analysis of isotopic composition of the gaseous hydrogen during the exchange reaction, the exchange rates of the individual steps, H₂ ? 2H(a) and H(a) + B ? H⁺B + e, of the hydrogen electrode reaction were determined at various hydrogen pressures and solution pH's, where H(a) is a hydrogen adatom and B = H₂O or OH^?. The rates of the steps were widely different among the metals studied but, throughout these metals, the hydrogen pressure dependence of the rate of the first step was with the power of 1·0–0·9, and that of the second step, 0·2–0·5. Both the rates were independent of solution pH. Generally, the former step is virtually rate-determining under low hydrogen pressures, whereas the latter takes over the role with increasing hydrogen pressure. Under ordinary pressures, the first step is virtually rate-determining on Pt but neither step is singly rate-determining on Rh and Ni.