Piezoelectric Response to Surface Stress Change of a Palladium Electrode in Sulfate Aqueous Solutions

The interfacial properties of palladium electrode in sulfate solutions of different pH values have been investigated using the piezoelectric response of surface stress change induced by a potential modulation. It was found from the piezoe-lectric signals that the potential of electrocapillary maximum, Emax or potential of zero charge (pzc) is present in the poten-tial region of hydrogen absorption into Pd. The pH dependence of pzc was measured in the range from pH 0.7 to 12.8. Below pH 6.0, pzc was close to the equilibrium potential of hydride formation. Above pH 6.0, pzc was higher than that of hydride formation. The piezoelectric signals obtained in the potential region of oxide formation suggested that sign-rever-sal of surface charge takes place in the potential range of PdO monolayer formation which is similar to Pt electrode. Many studies of hydrogen absorption into palladium electrode during electrolysis have been performed so far because of its large capacity of hydrogen absorption (1). Furthermore, the interfacial studies of palladium electrode have attracted special attention in relation to cold nuclear fusion which has been reported by Fleischmann etal. (2). The fundamental knowledge on electric double layer o