Ni₃N‑Coated Ni Nanorod Arrays for Hydrogen and Oxygen Evolution in Electrochemical Water Splitting

Designing high efficiency non-noble metal catalysts for electrochemical hydrogen and oxygen evolution reactions (HER and OER) is a challenging and promising task. In the present work, a large-scale self-supported black nickel sheet composed of nickel nanorod arrays (B-Ni) was successfully fabricated via electroplating with a nanostructured Si template assisted strategy, and Ni₃N coating layer was coated on the structured surface followed by a nitrogen plasma treatment with different treatment durations. The black color is due to the immensely enhanced light absorption through the surface nanostructures with high aspect ratio. The samples show promising catalytic performance when used as electrochemical catalysts for both HER and OER in alkaline electrolyte. Benefiting from the nanostructure and the Ni₃N coating, B-Ni_N₂_10 min exhibits low onset potentials of 1.560 and 0.165 V at a current density of 10 mA/cm² for OER and HER, respectively. The calculated electrochemical surface area (ECSA) for B-Ni is 10 times higher than the pristine Ni sheet (P-Ni), while after nitrogen plasma treatment, the ECSA for B-Ni_N₂_10 min is 21 times higher than that of the P-Ni. In addition, all the catalysts show good electrochemical stabilities. All the improvements for the electrochemical performances suggest that nanostructured nickel nitride could be a promising inexpensive catalyst system for both OER and HER processes.