Crystal lattice distortion in Se-doped CoMoO₄ inducing highly active γ-CoOOH species for efficient water oxidation

The self-reconstructed cobalt oxyhydroxides (CoOOH) evolved from pre-catalysts generally possess larger specific surface area and more active sites than the direct synthesized one, always showing better oxygen evolution reaction (OER) activity. However, subject to the spontaneous rearrangement of atoms, the reconstructed CoOOH typically exhibits β polymorphs, rather than γ-CoOOH with higher OER activity. Herein, a new strategy to affirmatively obtain γ-CoOOH is established through adjusting the phase transformation mechanism of CoMoO₄ by controllably doping Se atoms. The interstitial Se atoms in Se-CoMoO₄ introduce tensile strain and form high-spin state Co²⁺, creating the favorable lattice environment that inspires CoMoO₄ to reconstruct into γ-CoOOH rather than β-CoOOH. The reconstructed γ-CoOOH from Se-CoMoO₄ exhibits excellent OER activity, which is verified by a low overpotential of 332 mV at 1000 mA cm⁻², low Tafel slope (78.24 mV dec⁻¹) and long-term stability (over 200 h) in 1 M KOH electrolytes. This work offers a constructive idea to achieve the formations of high active phase, and can provide inspiration for the design of efficient catalysts with high performance.