Fast synthesis of nickel phosphide nanosheets for ultra-stable hydrogen evolution in seawater splitting†

Efficient and stable electrocatalysts that can drive the hydrogen evolution reaction (HER) in seawater splitting are highly desirable for hydrogen production. Heterometal-doped nickel phosphides are generally considered as a potential candidate due to their unique properties and synergistic effect, which accelerates the electron transfer kinetics and boosts the intrinsic activity. Herein, we prepared Co-doped Ni₅P₄ (Co–Ni₅P₄) under different calcination times by fast and one-step chemical vapor deposition, and for comparison, a series of Fe-doped Ni₅P₄ (Fe–Ni₅P₄) were also prepared by the same method. Different calcination times bring different HER activity and the Co–Ni₅P₄ prepared with 5 min calcination time (Co–Ni₅P₄-5m) exhibits a great catalytic activity, being higher than other Co–Ni₅P₄ and Fe–Ni₅P₄. In alkaline seawater, the overpotential needed for Co–Ni₅P₄-5m is only 74 and 162 mV to achieve the current density of 10 and 100 mA cm⁻², respectively. More importantly, Co–Ni₅P₄-5m exhibits great mechanical and electrochemical stability, and can be stably run under the current density of 100 mA cm⁻² for more than twenty days. The short synthesis time, great catalytic activity, and ultra-long-term stability make Co–Ni₅P₄-5m a suitable candidate in actual applications of seawater splitting for hydrogen.