The rate and extent of anion adsorption on electrocatalyst surfaces can have a major effect on the electrochemical kinetics of important fuel cell reactions such as hydrogen oxidation, methanol oxidation and oxygen reduction. Anion adsorption isotherms are generally difficult to measure, and little reliable data have been reported in the literature. The purpose of this work is to use the in situ Probe Beam Deflection (PBD) technique to study the rate and extent of anion adsorption at polycrystalline Pt electrode surfaces as a function of electrode potential. We have carried out a series of PBD experiments to detect the proton and anion fluxes that accompany the oxidation and reduction processes that proceed on Pt electrode surfaces in 0.1 M solutions of H3PO4, H2SO4 and HClO4. The measured beam-deflection signals exhibited a strong dependence on electrode potential and anion identity. We found that in all three electrolytes the onset of anion adsorption began at ~200 mV (vs the dynamic hydrogen reference electrode), i.e. within the potential range wherein adsorbed H2 is oxidized. We also confirmed that the presence of PO43- anions shifts the Pt oxidation reaction towards more positive potentials.
Brisard GM, Rudnicki JD, McLarnon FR, Cairns EJ. Application of probe beam deflection to study the electrooxidation of copper in alkaline media. Electrochim. Acta 1995; 40:859.
Deng Z, Spear JD, Rudnicki JD, McLarnon FR, Cairns EJ. Infrared-photothermal deflection spectroscopy: a new probe for the investigation of electrochemical interfaces. Paper no. 669 presented at the 187th Meeting of the Electrochemical Society, Reno, NV, May 1995.