Multifunctional Nickel–Cobalt Phosphates for High-Performance Hydrogen Gas Batteries and Self-Powered Water Splitting

Large-scale energy production and storage applications call for the development of advanced electrochemical systems including rechargeable batteries and water splitters, whose performances are largely determined by their active materials. In this work, we demonstrate an integrated hydrogen gas production and energy storage system by implementing a self-powered water splitter with hydrogen gas batteries. Such an integrated system is achieved by the application of a multifunctional nickel–cobalt phosphate (NCP) via a facile electrodeposition method. Due to the synergistic effect between Ni, Co, and phosphate ions, the NCP shows better redox reactions for energy storage and higher electrochemical activity than its hydroxide counterpart. When acting as a cathode, the NCP exhibits a high specific capacity of 278 mAh g–1 at 1.52 C, impressive rate performance, and outstanding cycling stability for over 12,000 cycles. Therefore, the assembled NCP–H2 battery based on the NCP cathode and H2 anode shows outstanding rate performance and long-term stability. Furthermore, an integrated water splitter using the NCP as bifunctional catalysts for hydrogen and oxygen evolution reactions is self-powered by the NCP–H2 battery, showing multifunctional properties of our NCP for potential energy production and storage applications.