Theoretical and experimental investigations of Co-Cu bimetallic alloys-incorporated carbon nanowires as an efficient bi-functional electrocatalyst for water splitting

Abstract

Application of noble metal-free electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) during electrocatalytic water splitting is crucial for clean energy conversion and has drawn extensive attention. However, the development of highly active and low cost electrocatalysts is a considerable challenge. Herein, Co-Cu alloy nanoparticles-incorporated carbon nanowires electrocatalyst was synthesized and evaluated for both OER and HER. The nanomaterials were fabricated by facile electrospinning of sol-gel composed of cobalt acetate, copper acetate, and poly(vinyl alcohol) followed by calcination in an inert environment. Adjusting the composition of the metallic counterpart was found to significantly enhance electrochemical properties of the catalyst. Furthermore, the unique nanowire morphology and structural properties of incorporated Co-Cu alloy, the (Co0.95Cu0.05@CNWs) composition exhibits good electrocatalytic performance for both OER and HER in the alkaline medium. Physicochemical characterizations using X-ray diffraction, X-ray photoelectron spectroscope, scanning electron microscopy, and transmission electron microscopy have confirmed the formation of alloy structure and nanowire morphology. The optimum composition (Co0.95Cu0.05@CNWs) requires small overpotential, ɳ10 of ∼285 mV for oxygen evolution reaction (OER) and ∼160 mV for hydrogen evolution reaction (HER) with the corresponding Tafel slope of 92 mV dec−1 and 172 mV dec−1 versus the reversible hydrogen electrode, respectively. In addition, only negligible loss in activity was observed after 1000 cycles and prodeces cell voltage of 1.58 V at current of 10 mA/cm2 and 1.72 V at current density of 50 mA/cm2 in two electrode system. Density Functional Theory (DFT) calculations were employed to verify experimental results. Electronic density of states (DOS) results reveal an increase in electronic states near the Fermi level upon Co-Cu heterojunctioning with CNWs. This is indicative of improved catalytic activity and more favorable binding energies of HER and OER intermediates. Reaction coordinate diagrams for HER and OER were developed, which aided in identifying thermodynamically limiting steps. This work may provide a feasible approach for incorporating other transition metals to design low-cost and high-performance bifunctional electrocatalysts for overall water splitting.