Nitrogen-doped carbon layer coated Co(OH)F/CoP 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/CoP catalyst NC@Co(OH)F/CoP/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 CoP 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/CoP/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. 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 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.