Pd–Ag hydrogen content and electrical resistivity: Temperature and pressure effect

A Pd–Ag (silver 21 wt.%) thin sheet has been tested in order to measure its electrical resistivity by means of electrochemical impedance spectroscopy under different hydrogenation conditions in the temperature range 25–350 °C. The metal sheet has been assembled with the electrical contacts in a gas tight module where pure hydrogen has been fed at a pressure of 100 and 200 kPa.The electrical resistivity vs. both the temperature and hydrogen pressure presents a characteristic S-shape curve with a minimum and a maximum of the resistivity. This behaviour permitted to recognize three stages: (1) introduction of H into Pd–Ag lattice up to a well-defined H/M ratio increases the resistivity; (2) further uptake of hydrogen with a decrease of resistivity until a higher H/M ratio; (3) above this higher H/M ratio the resistivity increases sharply.The behaviour of the electrical resistivity is discussed in details by considering the hydrogen uploading into the metal lattice, its effect on the conduction electrons and the scattering of the hydrogen atoms into the metal lattice.

► We measured the resistivity of a Pd–Ag alloy between 25 and 350 °C at 100 and 200 kPa. ► We analysed the characteristic S-shape curve. ► We correlated the resistivity to the H/M ratio. ► We recognized the main effects acting on resistivity contributing to this behaviour.