Transition metal‐based oxyhydroxides (MOOH) derived from the irreversible structural reconstruction of precatalysts are often acknowledged as the real catalytic species for the oxygen evolution reaction (OER). Typically, the reconstruction‐derived MOOH would exhibit superior OER activity compared to their directly synthesized counterparts, despite being fundamentally similar in chemistry. As such, structural reconstruction has emerged as a promising strategy to boost the catalytic activity of electrocatalysts. However, the in‐depth understanding of the origin of the superior OER activity of reconstructed materials still remains ambiguous, which significantly hinders the further developments of highly efficient electrocatalysts based on structural reconstruction chemistry. In this review, a comprehensive overview of the structural reconstruction behaviors in the reported reconstruction‐derived electrocatalysts is provided and the intrinsic chemical and structural origins of their high efficiency toward OER are unveiled. The fundamentals of structural reconstruction mechanisms, along with the recommended characterization techniques for the understanding of the dynamic structural reconstruction process and analyzing the structure of real catalytic species are also interpreted. Finally, in view of structural reconstruction chemistry, the potential perspectives to facilitate the design and synthesis of highly efficient and durable OER electrocatalyst are presented.

Cobalt oxyhydroxide (CoOOH) is a promising catalytic material for oxygen evolution reaction (OER). In the traditional CoOOH structure, Co³⁺ exhibits a low-spin state configuration ( $${t}_{2{{{{{\rm{g}}}}}}}^{6}{e}_{{{{{{\rm{g}}}}}}}^{0}$$t 2 g 6 e g 0 ), with electron transfer occurring in face-to-face $${t}_{2{{{{{\rm{g}}}}}}}^{*}$$t 2 g * orbitals. In this work, we report the successful synthesis of high-spin state Co³⁺ CoOOH structure, by introducing coordinatively unsaturated Co atoms. As compared to the low-spin state CoOOH, electron transfer in the high-spin state CoOOH occurs in apex-to-apex $${e}_{{{{{{\rm{g}}}}}}}^{*}$$e g * orbitals, which exhibits faster electron transfer ability. As a result, the high-spin state CoOOH performs superior OER activity with an overpotential of 226 mV at 10 mA cm⁻², which is 148 mV lower than that of the low-spin state CoOOH. This work emphasizes the effect of the spin state of Co³⁺ on OER activity of CoOOH based electrocatalysts for water splitting, and thus provides a new strategy for designing highly efficient electrocatalysts.