Electro-Oxidation of Borohydride on Rhodium, Iridium, and Rhodium–Iridium Bimetallic Nanoparticles with Implications to Direct Borohydride Fuel Cells

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