Kinetic Study of the Oxygen Reduction Reaction on α-Ni(OH) 2 and α-Ni(OH) 2 Supported on Graphene Oxide

Abstract

The kinetics of the oxygen reduction reaction on α-Ni(OH)2 and α-Ni(OH)2 supported on graphene oxide (α-Ni(OH)2/GO) were investigated using rotating disk linear sweep voltammetry in alkaline solutions of varying oxygen and hydroxyl concentrations. Over the full hydroxyl concentration range (0.05 M to 0.5M), α-Ni(OH)2/GO displayed higher activity than unsupported α-Ni(OH)2. The electron transfer numbers were 2.9 ±0.2 for α-Ni(OH)2, 3.4 ±0.1 for α-Ni(OH)2/GO at low [OH-], and 3.8-3.9 for α-Ni(OH)2/GO at high [OH-]. Compared to α-Ni(OH)2, α-Ni(OH)2/GO displayed higher chemical reaction rate constants and higher electron transfer rate constants. These differences suggest that the synergy between the α-Ni(OH)2 catalyst and the graphene oxide support is related to increases in both the speed of the rate determining chemical step and the facility for electron transfer. The order of reaction with respect to oxygen was ∼1 for α-Ni(OH)2 and α-Ni(OH)2/GO. The order of reaction with respect to hydroxyl was ∼0 for α-Ni(OH)2 and α-Ni(OH)2/GO. The first order reaction with respect to oxygen is precedented, but the zero reaction order with respect to hydroxyl is particular to the α-Ni(OH)2 catalysts. The zero reaction order is explained by possible decoupling of solution and catalyst surface hydroxyl concentrations.