Nitrogen-doped carbon layer coated Co(OH)F/CoP2 nanosheets for high-current hydrogen evolution reaction in alkaline freshwater and seawater

Utilizing renewable energy such as offshore wind power to electrolyze seawater for hydrogen production offers a sustainable development pathway to address energy and climate change issues. In this study, by incorporating nitrogen-doped carbon quantum dots (N-CDs) into precursors, we successfully synthesized a nitrogen-doped carbon (NC)-layer-coated Co(OH)F/CoP₂ catalyst NC@Co(OH)F/CoP₂/NF loaded on nickel foam (NF). The introduction of N-CDs induced significant morphology change of the catalyst, facilitating the exposure of numerous active sites, ensuring the presence of catalytically active species CoP₂ in nanoparticle form and avoiding agglomeration, which was advantageous to enhancing the overall hydrogen evolution reaction (HER) activity of the catalyst. The formation of Co-N bonds accelerated electron transfer, regulated the electronic structure, and optimized the catalyst's adsorption capacity for H* intermediates, which resulted in remarkably improved HER performance. In addition, Co(OH)F can also serve as a structural support, preventing the catalyst from collapsing during the HER catalytic process. NC@Co(OH)F/CoP₂/NF exhibited excellent HER activity in alkaline freshwater and alkaline seawater, respectively requiring overpotentials of only 107 and 128 mV to achieve a current density of 100 mA cm^-2. More importantly, it also demonstrated excellent HER activity at high current densities, with overpotentials of 189 and 237 mV at a current density of 1000 mA cm^-2 in alkaline freshwater and alkaline seawater, respectively. This work provides new insights into the design and construction of highly efficient HER catalysts for applications in alkaline freshwater and seawater.