Composition- and structure-tunable CoNiFe hydroxide nanostructures toward enhanced oxygen evolution reaction

The electrocatalytic performance of transition-metal layered double hydroxides (LDHs) can be substantially enhanced through compositional and structural engineering. Herein, ternary (CoNiFe) hydroxide nanocones featuring mixed tetrahedral (T_d) and octahedral (O_h) coordination are rationally designed to boost oxygen evolution reaction (OER) activity. Binary CoNi hydroxide nanocones with mixed coordination are first synthesized, among which a Co : Ni ratio of 3 : 1 exhibits optimal performance with an overpotential of 339 mV at 10 mA cm^-2. Subsequent Fe incorporation followed by a topochemical oxidative intercalation process convert the CoNiFe(II) hydroxides into CoNiFe(III) LDHs while retaining mixed T_d/O_h coordination. Benefiting from the synergistic effects of multimetal composition and coordination modulation, the resulting Co₃Ni₁Fe₁ LDH nanocones achieve a markedly reduced overpotential of 280 mV. Furthermore, exfoliation into monolayer nanosheets leads to a further enhancement in catalytic activity by increasing exposure of accessible active sites, ultimately lowering the overpotential to 267 mV. This study highlights an effective strategy that integrates compositional optimization, coordination engineering, and structural modulation for the development of high-performance LDH electrocatalysts.