Monodisperse Pd nanoparticles assembled on reduced graphene oxide-Fe3O4 nanocomposites as electrocatalysts for borohydride fuel cells

Abstract

5 nm palladium nanoparticles (Pd NPs) are synthesized and assembled on reduced graphene oxide-iron oxide nanocomposite (rGO-Fe3O4) to be used in oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) studies in alkaline media. The structure and morphology of the resulting Pd/rGO-Fe3O4 hybrid material are evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) analyses. The electrochemical behavior of Pd/rGO-Fe3O4 hybrid material for the ORR and BOR is investigated by voltammetry with rotating disk and rotating ring disk electrode and electrochemical impedance spectroscopy, enabling evaluation of the number of exchanged electrons, Tafel slope, exchange current density and activation energy. The results reveal that ORR at Pd/rGO-Fe3O4 proceeds as a 2-electron process with Tafel slope of 0.133 V dec−1, while BOR proceeds as a 5.6-electron process with Tafel slope of 0.350 V dec−1 and exchange current density of 1.38 mA cm−2. The BOR activation energy was found to be 12.4 kJ mol−1. Overall, this study demonstrates the good efficiency of Pd/rGO-Fe3O4 hybrid material for BOR.