ELECTROCHEMICAL MECHANISMS OF NOBLE-METAL/HYDROGEN SYSTEMS. PART II. PALLADIUM

The hydrogen-predncing reactions on a beta -palladium cathode were investigated and mechanisms were determined. By means of a palladium bielectrode it was possible to determine mechanisms on the anode and cathode surfaces of alpha -palladium and to study the migration of protons through the bielectrode. The relation between the hydrogen content of palladium and the resistance and potential was determined. The equilibrium potential anomalies in the palladium/ hydrogen system were resolved by showing that the potential-determining reaction for alpha -palladium is an equilibrium between hydrogen ions in solution and hydrogen dissolved in the metal, whereas the potential-determining reaction on beta -palladium is an equilibrium between hydrogen ions in solution and molecular hydrogen. It was also shown that when palladium is electrolytically changed with hydrogen its electrochemical behavior is different from that of palladium charged by exposure to hydrogen gas. The thermodynamics of these systems are discussed and a structural interpretation of the free energy relations is given. The mechanisms of the spontaneous solution of hydrogen in pure palladium in aqueous solution are given. (auth)