Transition-metal hydroxide nanosheets with peculiar double-layer structures as efficient electrocatalysts

Single- or few-layer nanosheets with a molecular-level thickness may provide an ideal model for the fundamental investigation of layer-number-dependent properties. Herein, we report a new strategy for a selective synthesis of transition-metal-containing Co-Fe and Co-Ni-Fe hydroxide nanosheets with peculiar double-layer structures. A unique second-stage phase was obtained from topochemical oxidative intercalation of brucite-type metal hydroxides, e.g., Co5/6Fe1/6(OH)2 and Co2/3Ni1/6Fe1/6(OH)2, with a molar ratio of Fe fixed at 1/6. After anion exchange, the second-stage phase was exfoliated into double-layer hydroxide nanosheets with an average thickness of ∼1.9 nm, which was approximately twice that of their single-layer counterparts (∼1.0 nm). Electrocatalytic measurements combined with theoretic calculations revealed that the double-layer hydroxide nanosheets exhibited excellent oxygen evolution reaction (OER) catalytic activity and kinetics, outperforming their single-layer counterparts, which validates the great potential of transition-metal hydroxide nanosheets with both tunable composition and layer numbers for efficient electrocatalysis.