Abstract
Bimetallic nanoparticles of Au and Ni in the form of alloy nanostructures with varying Ni content are synthesized on reduced graphene oxide (rGO) sheets via a simple solution chemistry route and tested as electrocatalysts towards the hydrogen evolution (HE) and oxygen reduction (OR) reactions using polarization and impedance studies. The Au Ni alloy NPs/rGO nanocomposites display excellent electrocatalytic activity which is found to improve with increasing Ni content in the Au Ni/rGO alloy nanocomposites. For HER, the best Au Ni alloy NPs/rGO electrocatalyst, the one with the highest Ni content, exhibits high activity with an onset overpotential approaching zero versus the reversible hydrogen electrode and an overpotential of only 37 mV at 10 mA cm(-2). Additionally, a low Tafel slope of 33 mV dec(-1) and a high exchange current density of 0.6 mA cm(-2) are measured which are very close to those of commercial Pt/C catalyst. Also, in the ORR tests, this electrocatalyst displays comparable activity to Pt/C. The Koutecky Levich plots referred to a 4 electron mechanism for the reduction of dissolved O-2 on the Au Ni alloy NPs/rGO catalyst. The electrocatalyst thus demonstrates excellent activity towards HER and ORR. Additionally, it exhibits outstanding operational durability and activation after 10,000th cycles assuring its practical applicability. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.