Core-shell of Tin - Palladium Bimetallic Electrocatalysts for Hydrogen Oxidation Reaction in Alkaline Electrolyte

The kinetics of hydrogen oxidation reaction (HOR) in alkaline electrolyte is remarkably slower (≈ two order of magnitude) than in acid electrolyte on the state-of-the-art Pt. Hence the loading of precious metal is about five times higher to match the performance of proton exchange membrane fuel cells. We have studied highly active Pt-free catalysts for HOR based on palladium and tin in a core-shell architecture. Freshly prepared Sn nanoparticles are reacted with Pd²⁺ or a Pd-Sn chloride complex solution in a galvanic displacement reduction to form Pd or Pd_x-Sn_x of few nanometers on metallic Sn. These bimetallic particles were characterized by various techniques including XRD, Raman spectroscopy, XPS, SEM as well as standard electrochemical measurements. The HOR parameters calculated from voltammograms obtained from rotating disc electrode experiments are zero overpotential (vs RHE), exchange current density of 0.13 mA/cm² and Tafel slope of ~150 mV decade^-1. Alkaline exchange membrane fuel cell employing Sn@PdSn anode shows higher power output than Pd on high surface area carbon measured under the same conditions.