In electrochemical devices containing the catalyst layer \proton exchange membrane (PEM) interface, surface diffusion of the adsorbed intermediates impels the catalytic sites that are not in direct contact with the PEM to be involved in the interfacial reaction, and thus increases the utilization rate of catalysts [J. McBreen, J. Electrochem. Soc. 132 (1985) 1112; C.S. Cha, Introduction to the Kinetics of Electrode Processes, Science Press, Beijing, 2002 (Chapter 9)]. However, up to now, there have been few methods for studying the surface diffusion existing in these systems. In this paper, a special experimental device containing the An plane\H+-Nafion(R) interface was designed as a simplified model of the powder catalyst\PEM assemblies to study surface diffusion and the recombination reaction of the overpotential deposition (opd) hydrogen atoms in the process of the her. In the chronoamperometric experiments, the excess experimental current, due to surface diffusion and the recombination reaction of the opd hydrogen atoms, was obtained, and the numerical analysis of the excess experimental current was performed. Then the surface diffusion coefficient and the recombination reaction rate constant of the opd hydrogen atoms on the An surface were obtained by fitting these current-time data. The results showed that the opd hydrogen atoms could diffuse quickly on the Au surface and the average value of their surface diffusion coefficient is about 1.47 x 10(-3) cm s(-1). (C) 2003 Elsevier B.V. All rights reserved.