Redox-Functional NiFeV/Ni 3 Fe Bilayer Electrodes to Achieve High Energy-Efficient Alkaline Water Electrolysis at 1000 mA/cm 2 under Ambient Conditions

Water electrolysis powered by renewable energy is crucial for producing green hydrogen, offering a sustainable alternative to fossil fuels. However, production costs must be significantly reduced to compete with hydrogen derived from fossil fuels. Despite decades of research in electrocatalyst development, advancements at the laboratory scale, such as catalyst design and mechanistic insights, have yet to address the critical challenge of developing catalysts that combine high stability with the required performance at high current densities for practical applications. Developing an electrolyzer capable of delivering high energy efficiency at room temperature (RT) is essential for reducing operational costs and prolonging the lifetime of the green hydrogen system. Our redox-functional NiFeV/Ni3Fe bilayer catalyst is designed to meet the targets set by IRENA for energy efficiency, energy consumption, and hydrogen production cost. The NiFeV/Ni3Fe electrolyzer shows significant promise, achieving energy efficiencies of 72.1% and 70% at 500 and 1000 mA/cm2, respectively, at room temperature. The cell operates at a low potential of 1.8 V at 1000 mA/cm2, resulting in an energy consumption of 4.264 kWh/Nm3 or 47.4 kWh/kg·H2, approaching the IRENA target of 42 kWh/kg·H2 by 2050. In situ Raman spectroscopy was conducted to gain deeper insights into the active phases during OER. The NiFeV/Ni3Fe undergoes reconstruction, during which γ-NiOOH initially forms at low anodic bias. As the potential increases, γ-NiOOH transitions to β-NiOOH, followed by the further formation of γ/β-FeOOH, which serves as the active intermediate species to drive OER.