Nickel–Cobalt Hydrogen Phosphate on Nickel Nitride Supported on Nickel Foam for Alkaline Seawater Electrolysis

Developing high-performance non-noble bifunctional catalysts is pivotal for large-scale seawater electrolysis but remains a challenge. Here we report a sandwichlike NiCo(HPO₄)₂@Ni₃N/NF (denoted by NiCoHPi@Ni₃N/NF) catalyst. Vertical Ni₃N nanosheet arrays are first grown and supported on nickel foam, and then a bimetallic NiCoHPi coating is decorated on Ni₃N nanosheets by one-step electrodeposition. The hierarchical sandwich like structure offers a large surface area and plenty of catalytic active sites, and the coupling of interconnected Ni₃N and NiCoHPi accelerates the electron transfer. Moreover, the surficial hydrogen phosphate ions contribute to a proper OH^- absorption capacity due to the Lewis acid-base reaction. As a result, the NiCoHPi@Ni₃N/NF catalyst exhibits good OER and HER activity, requiring overpotentials of 365 mV (for OER) and 174 mV (for HER) to deliver 100 mA cm^-2 in the alkaline simulated seawater electrolyte. When assembled the NiCoHPi@Ni₃N/NF catalyst as both the anode and cathode, it only needs 1.86 V to reach 100 mA cm^-2 in alkaline simulated seawater electrolyte. This work may inspire the design and exploration of self-supported hierarchical composite electrocatalysts for hydrogen production from the electrolysis of seawater.