Electro-oxidation of borohydride on rhodium, iridium, and rhodium-iridium bimetallic nanoparticles with implications to direct borohydride fuel cells

Abstract

Electrochemical oxidation of borohydride is studied on nanosized rhodium, iridium, and bimetallic rhodium-iridium catalysts supported onto Vulcan XC72R carbon. The catalysts are characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy in conjunction with cyclic voltammetry and polarization studies. The studies reveal that a 20 wt % bimetallic Rh-Ir catalyst supported onto carbon (Rh-Ir/C) is quite effective for the oxidation of borohydride. Direct borohydride fuel cell with Rh-Ir/C as the anode catalyst and Pt/C as the cathode catalyst exhibits a peak power density of 270 mW/cm² at a load current density of 290 mA/cm² as against 200 mW/cm² at 225 mA/cm² for Rh/C and 140 mW/cm² at 165 mA/cm² for Ir/C while operating at 80°C. The synergistic catalytic activity for the bimetallic Rh-Ir nanoparticles toward borohydride oxidation is corroborated by density-functional theory calculations using electron-localization function.