Nickel/Carbide Based Catalysts for Oxygen Evolution Reaction in Alkaline Solution

Abstract

Hydrogen, produced by electrolysis, is one of the most promising means to store electricity coming from renewables and to address its intermittency. Due to the increase of global electricity share from renewable energy sources, large-scale storage systems are required. Alkaline electrolysis can be a suitable solution for the large-scale energy storage system. However, high overpotential and slow kinetics, particularly of the oxygen evolution reaction (OER), still limit the efficiency of the system. To enhance the efficiency of alkaline electrolysis cells, catalysts with high electrocatalytic activity for OER should be developed. Platinum-like behavior of tungsten carbide in surface catalysis was first discovered by Levy and Boudart in 1973[1]. In addition, tungsten carbide was reported to have a Pt-like electronic structure by Colton in 1975[2]. Since then, tungsten carbide has been studied widely and expected to replace noble metal catalysts which are used in many electrochemical reactions. In this study, we researched tungsten carbide as a support for nickel, and formation of bi-metallic surfaces for developing a high activity OER catalyst. WC was synthesized by two-steps. First, WC-Co was synthesized by heat treatment. Carbon nitride (g-C3N4) and tungsten chloride were used as a carbon and tungsten precursor. Cobalt precursor was also used to help carburization of tungsten. After synthesizing WC-Co, the acidic leaching process was followed by using sulfuric acid (H2SO4) to eliminate cobalt. Through additional mixing with 3d metal precursors and heat treatment, Ni/WC and NiFe/WC were synthesized. Furthermore, Ni/C was also prepared using same precursors as a counter group. Figure 1 shows the SEM images of the synthesized WC and Ni/WC. Cyclic voltammetry was performed to evaluate OER activity in 1 M KOH in potential range from 1 to 1.8 V. Figure 2 shows the OER catalytic activities of synthesized catalysts and Ir/C. Pure WC and Ni/C had 430 mV and 394 mV overpotential at 10 mA∙cm-2 respectively. In 3d Metal/WC cases, Ni/WC and NiFe/WC showed only 335 mV and 314 mV overpotential at 10 mA∙cm-2. Both catalysts had higher electrocatalytic activity for OER than Ir/C in alkaline media.