Multi-metal oxide catalyst for electrochemical water oxidation

Abstract

Increasing popularity in hydrogen economy and environment sustainability as an alternative source for energy is strategic for bringing greenhouse gas emissions to net zero. Water splitting process is promising technology for producing hydrogen compared to steam methane reforming. However, the process is limited by sluggish oxygen evolution reaction kinetics which could be overcome by an effective electrocatalyst.

Spinel oxides are promising for electrochemical OER. However, the activity is relatively low. Doping strategy is a key factor to increase the conductivity and improve the OER catalytic activity of such oxides. In this study, spinel NiCo2O4 is prepared using simple hydrothermal synthesis followed by annealing at various temperatures. The optimal catalytic activity of NiCo2O4 is achieved through the variation of synthetic parameters. Afterwards, molybdenum (Mo) dopant is successfully incorporated into the crystal lattice of spinel oxide, NiCo2O4. The crystal structure and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscope with energy dispersive x-ray (SEM-EDX), respectively. Optimizing the Mo dopant ratio results in high OER catalytic activity with overpotential lower than that for pristine NiCo2O4 by 100 mV at current density of 10 mA cm–2. Mo-doped NiCo2O4 shows also excellent catalytic activity on Ni foam (small overpotential of 265 mV at 10 mA cm–2) revealing its high intrinsic activity. Tafel plot analysis and electrochemical impedance spectroscopic analysis demonstrate the fast surface kinetic of Mo-doped NiCo2O4 and rapid charge transfer across the electrode/electrolyte interface, respectively. The catalyst also shows high stability at different potential values, particularly at high potential value of 1.7 V vs. RHE which is important for practical application. Our work provides systematic study for the optimization of pristine- and Mo-doped-spinel oxides to achieve high catalytic activity. This study can also help in the development of new catalyst using simple dopant strategy with enhanced OER catalytic activity.