Study of the hydrogen electrode reaction on Pt/Bi(ad) electrodes

P.M. QUAINO; M.R. GENNERO DE CHIALVO; A. C. CHIALVO

Sao Pedro

Congreso; 54th Annual Meeting of the International Society of Electrochemistry; 2003

International Society of Electrochemistry

It is widely accepted that the adsorbed hydrogen that participates as intermediate in the hydrogen evolution reaction (her) is not the so-called HUPD, but a much more weakly adsorbed hydrogen atom called HOPD. It is also well known that, in order to be irreversibly adsorbed, an adatom must occupy a high energy adsorption site. Therefore, the irreversible adsorption of any adatom would displace the HUPD atoms and would not influence the electrocatalytic activity of the her. There are some evidences in the literature that the irreversible adsorption of bismuth on platinum for the her produces an apparent decrease of the electrocatalytic activity with the increase in the surface coverage of Bi(ad), which was justified on the basis of the inhibition of the HUPD. The objective of the present work is to determine if the irreversible adsorption of Bi on Pt can take place on the sites occupied by the HOPD atoms. Therefore, the hydrogen electrode reaction (HER) was studied through the experimental determination of the dependence of the current on overpotential, in the potential region near the equilibrium state. The working electrode was a roughness platinum wire, with roughness factors ranging between 20 and 40. The electrolyte solution was 0.5M H2SO4 saturated with hydrogen gas at 25°C. The purity of the solution was controlled through a slow potentiodynamic sweep applied after a cathodic potentiostatisation during 30 min. The adsorption of Bi was carried out at a controlled potential (-0.05 V < Ead < 0.05 V, vs. RHE) during different times (30 s < tad < 180 s). The amount of Bi(ad) was evaluated through the conventional method, from the fraction of surface inhibited by the HUPD atoms.