Investigation of NiCoOx catalysts for anion exchange membrane water electrolysis: Performance, durability, and efficiency analysis

Anion exchange membrane (AEM) water electrolysis is a promising method for hydrogen production using inexpensive metal oxide catalysts. This study investigates the catalytic activity and performance of nickel cobalt oxide (NiCoOx) catalysts in AEM water electrolysis for hydrogen production. The catalysts were synthesized with varying ratios of Ni to Co. The NiCoOx catalysts were coated on nickel foam gas diffusion layer (GDL) at the anode. Scanning electron microscopy (SEM) analysis revealed a distinct flaky structure of the NiCoOx catalyst. X-ray diffraction (XRD) studies confirmed the presence of NiCo2O4 spinel crystal structure in the catalysts. Linear sweep voltammetry (LSV) measurements for Oxygen evolution reaction (OER) in three electrode systems showed that NiCoOx (1:3) exhibited the highest catalytic activity, with a current density of 238 mA cm−2 at 1.8 V. Tafel analysis indicated that NiCoOx (1:3) had the lowest Tafel slope, suggesting faster reaction kinetics and lower overpotential for higher current density. Chronoamperometry tests demonstrated the stability of the catalysts at various current densities, and long-term stability testing of NiCoOx (1:3) for 500 h revealed minimal voltage increase during OER, demonstrating its stability in prolonged operation. NiCoOx (1:3) displayed the highest activity among the catalysts at different temperatures, with current densities reaching 1700 mA cm−2 at 2.2 V and 70 °C for single-cell electrolysis. The Nyquist plots and equivalent circuit analysis reveal that the NiCoOx (1:3) catalyst exhibits lower activation resistance and higher efficiency in oxygen evolution reaction compared to other catalyst compositions. Temperature-dependent measurements demonstrate decreased resistances (ohmic, activation, and membrane) with increasing temperature, indicating improved reaction kinetics and ion conductivity. Long-term durability tests reveal the stable operation of the catalyst, while short-term tests confirm its effectiveness at higher current densities for single-cell electrolyzer operation. These findings highlight the importance of electrochemical Impedance Spectroscopy (EIS) and equivalent circuit fitting in optimizing AEM water electrolysis performance, aiding the development of efficient and durable electrolyzers for hydrogen production.