Combined Electrochemical and Photovoltaic Studies of the Galena-Electrolyte Interface

Abstract

The electrophysical changes of a galena electrode undergoing forced and open-circuit reactions have been studied using electrochemical measurements with simultaneous measurements of the surface photovoltage (SPV). These measurements have provided some insight into the relationship between surface reactions, the accompanying changes in the stoichiometry of the electrodes, and the surface potential. Measurements are reported for both polished galena surfaces and for fresh surfaces produced by in situ cleavage under 0.1 M sodium tetraborate. The SPV results indicate that at the rest-potential, the surface potential of degenerate n-type and slightly p-type galena is large and negative, corresponding to an electron-deficient or hole-rich space charge. During reduction, the apparent flat-band potential occurs at -0.42 V (SeE) for the p-type and at -0.65 V for the n-type electrode. The SPV measurements on cleaved surfaces indicate the surface potential is zero at cleavage. They also show the progressive development of a negative surface potential with subsequent open-circuit oxidation. The results are interpreted using a model based on associating lead vacancies with acceptor-like surface states and sulfur vacancies with donor-like surface states, and assuming densities dependent on past electrochemical treatment.