Engineering Palladium Surfaces to Enhance the Electrochemical Storage of Hydrogen

Abstract

Materials can be engineered to have enhanced hydrogen storage capabilities for a given electrolysis working condition by modifying the composition of the first few atomic layers. The changes in composition of the near surface can affect the balance between the Volmer, Tafel, and Heyrovsky reactions, which changes the chemical potential of the adsorbed hydrogen, and ultimately controls the electrochemical insertion of hydrogen. To this end, the hydrogen stored under galvanostatic conditions was investigated after altering the composition of the Pd surface with various combinations of Pb, Bi, and Pt. It was found that the addition of an underpotential deposition (UPD) of Bi on the Pd cathode increases the hydrogen content from PdH0.77 to PdH0.81 at −10.9 mA cm−2, and the addition of a small amount of Pt to the UPD Bi (Pt/Bi atomic ratio of 0.13 ± 0.01) further increased the hydrogen content to PdH0.87. For comparison, the same change in hydrogen content from pressurized gas loading experiments would require an increase in hydrogen fugacity from about 16 to 2400 atm. This work provides a fundamental basis for the future design of surface alloys yielding enhanced electrochemical hydrogen storage in Pd and other hydrogen absorbing materials.