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 SrCoO_3-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 t_2g* orbitals, populating more electronic states around the Fermi level and hence significantly enhancing the electron transfer ability and corresponding OER activity. Consequently, the reconstructed Ba_0.3Sr_0.7CoO_3-δ-h with the strongest t_2g* 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.