Pivotal Role of A‑Site Cation Intercalation in Reconstructed Perovskites for Enhanced Water Splitting

The reconstruction of perovskite oxides into transition metal oxyhydroxides (MOOH) has reshaped traditional structure–activity paradigms in oxygen evolution reaction (OER) catalysis. Understanding the structural origins of catalytic activity in reconstruction-derived MOOH is important for rationally optimizing its catalytic activity. Herein, by achieving complete reconstruction of SrCoO3‑δ, we show that A-site Sr actively participates in the formation of γ-CoOOH through intercalation. To explore the way and extent to which the A-site species can modulate the structure and catalytic performance, Ba is further introduced into the γ-CoOOH interlayer with varying Ba/Sr ratios. The disparity in atomic radius between Ba and Sr induces a local compressive strain in γ-CoOOH, resulting in distortion of the CoO6 octahedron. This structural distortion could lift the degeneracy of t2g* orbitals, populating more electronic states around the Fermi level and hence significantly enhancing the electron transfer ability and corresponding OER activity. Consequently, the reconstructed Ba0.3Sr0.7CoO3‑δ-h with the strongest t2g* band broadening exhibits superior OER activity, achieving 4.06 A cm–2 at 2.0 V in an anion exchange membrane water electrolyzer device and operating stably at 1 A cm–2 for more than 200 h. This work highlights the pivotal role of A-site cations in manipulating the reconstruction of perovskite precatalysts and offers a design principle for developing highly efficient OER electrocatalysts.