Reduced Graphene Oxide-Supported Nickel(II)-Bis(1,10-Phenanthroline) Complex as a Highly Active Electrocatalyst for Ethanol Oxidation Reaction

Abstract

The reduced graphene oxide (rGO) is used to support nickel(II)-bis(1,10-phenanthroline) complex (Ni(II)(Phen)2), forming a catalyst Ni(II)(Phen)2/rGO for ethanol oxidation reaction (EOR). A pyrolytic graphite electrode modified by this catalyst shows excellent electrocatalytic EOR activity, characterized by physical and electrochemical methods. The electrocatalytic activity of the material was evaluated by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). The significant increase in EOR currents compared to the electrode modified with only (Ni(II)(Phen)2 complex demonstrates the promotion role of the rGO. It is believed that the interaction between Ni(II)(Phen)2 and rGO to create a synergistic effect of Ni(II)(Phen)2/rGO catalyst should be responsible for the observed enhancement of the catalytic EOR performance. Using the Laviron theory, the charge transfer rate constant (ks) and the electron transfer coefficient (α) of the electrode reaction are calculated to be 0.60 s−1 and 0.61, respectively. Both the effects of OH− and ethanol concentration on the catalyst EOR activity are also studied to obtain the diffusion coefficient of ethanol (D = 4.7 × 10−6 cm2 s−1) and the catalytic rate constant (kcat = 1.26 × 107 cm3 mol−1 s−1). Based on the experimental results, an EOR mechanism catalyzed by Ni(II)(Phen)2/rGO is proposed. The catalytic EOR peak currents exhibit a linear growth (behavior) with increasing ethanol concentration, suggesting the possible use of this catalyst material as a sensor for ethanol analysis. In addition, the obtained chronoamperometric curves confirm the stability of the catalyst. It is believed that this Ni(II)(Phen)2/rGO catalyst is a promising cost-effective alternative for ethanol oxidation reaction in direct ethanol fuel cells.