A

The hydrogen electrode reaction (HER) on Pt electrode in a H2SO4 solution when CO gas was injected/stopped was studied using polarization resistance curve. In order to elucidate and confirm the CO poisoning effect, a few curve techniques were proposed. Applying them, the kinetic parameters such as the number of electrons transferred (z) and the cathodic transfer coefficient αc were determined. The HER in a 0.5 mol dm−3 H2SO4 solution saturated with H2 was confirmed as a reversible reaction having z = 2. When the above solution was injected with CO, the reversible HER changed to an irreversible reaction having z = 1 and αc ≈ 0.6. Once we stopped the CO injection, alteration from the irreversible to quasireversible reaction was gradually made after several cyclic polarizations. The proposed curve techniques can provide a reliable way to determine the kinetic parameters changing among reversible, irreversible, and quasireversible reactions.