Fabrication of nanoporous Ni and NiO via a dealloying strategy for water oxidation catalysis

Nickel oxides and (oxy)hydroxides are promising replacements for noble-metal-based catalysts owing to their high activity and good long-term stability for the oxygen evolution reaction (OER). Herein, we developed nanoporous Ni by a method of combined rapid solidification and chemical dealloying. Subsequently, nanoporous NiO was obtained via heating treatment, the macropore and skeleton sizes of the NiO originated from Ni10Al90 alloy are 100–300 nm and 80–200 nm, respectively. Benefiting from the multi-stage nanoporous structure and high specific surface area, the nanoporous NiO demonstrates an outstanding OER, reaching 20 mA cm−2 at an overpotential of 356 mV in 1 M KOH. The corresponding Tafel slope and apparent activation energy are measured to be 76.73 mV dec−1 and 29.0 kJ mol−1, respectively. Moreover, kinetic analysis indicates that the NiO catalyst shows pseudocapacitive characteristics, and the improved current is attributed to the high-rate pseudocapacitive behavior that efficiently maintains increased nickel redox cycling to accelerate the reaction rates. After 1000 cycles of voltammetry, the overpotential of the NiO decreases by 22 mV (j = 10 mA cm−2), exhibiting excellent stability and durability.