Hexagonal Phase Ni₃Fe Nanosheets toward High‐Performance Water Splitting by a Room‐Temperature Methane Plasma Method

Abstract In addition to tuning the size and shape, exploring highly efficient and cost‐effective catalysts with active metastable phase represents an alternative strategy to improve electrocatalytic water splitting performance. However, it still remains a big challenge to synthesize unconventional crystal structures under mild conditions. Herein, a facile CH₄ plasma assisted strategy to synthesize hexagonal close‐packed (hcp) Ni₃Fe/C porous nanosheets by in situ topology reduction of Ni₃Fe‐LDH nanosheets is successfully developed. Compared with its face‐centered cubic phase counterpart (fcc‐Ni₃Fe/C), the resulting hcp‐Ni₃Fe/C catalyst exhibits much enhanced activity with overpotentials of 70 and 201 mV at a current density of 10 mA cm⁻² for the hydrogen evolution reaction and oxygen evolution reaction, respectively. Moreover, a small cell voltage of 1.54 V is realized to drive overall water splitting. Theoretical calculations further reveal that hcp‐Ni₃Fe allows energetically favorable adsorption and dissociation of H₂O molecules. This work presents a new strategy for designing advanced metastable phase electrocatalysts with high performance for energy and environmentally relevant reactions.