Decoupled hydrogen and oxygen evolution for efficient water splitting by using nickel hydride batteries

Abstract

Cost-effective alkaline water splitting represents a promising and sustainable approach for hydrogen production. However, the prevention of hydrogen/oxygen mixing and the efficient use of unstable renewable energy are challenging issues. Herein, we propose a novel solution involving the integration of a nickel-metal hydride (Ni-MH) battery as a redox mediator and affordable a NiFe LDHs–NiFe alloy gradient hybrid bifunctional catalysts as gas evolution electrodes, effectively decoupling the hydrogen and oxygen evolution processes during water splitting. Then, the hydrogen evolution reaction (HER) cell using hydrogen storage alloy and catalytic electrode only requires 0.28 V and the oxygen evolution reaction (OER) cell using nickel hydroxide and catalytic electrode only requires 0.25 V to reach a high current density of 100 mA cm−2. Furthermore, a NiOOH-Zn cell is introduced as an alternative, replacing the OER reaction with Zn. This NiOOH-Zn cell can be discharged without further energy input. Moreover, such a decoupled water electrolysis system can seamlessly integrate with a Ni-MH battery, providing the flexibility to efficiently convert renewable energy sources into both hydrogen and electricity. This integrated system maximizes the utilization of renewable energy, making a significant contribution to sustainable energy production.