Comparative\nStudy on the Electrocatalytic Performance\nof ABO<sub>3</sub>‑Based Hexagonal Perovskite Oxides with Different\n[AO<sub>3</sub>] Layers

To systematically investigate the influence of the number\nof [AO<sub>3</sub>] layers in the unit cell of hexagonal perovskite\noxide on\nthe oxygen evolution reaction performance, we successfully synthesized\nthe three new hexagonal perovskite oxides 2H-BaCo<sub>0.9</sub>Ru<sub>0.1</sub>O<sub>3−δ</sub>, 6H-BaCo<sub>0.9</sub>Ru<sub>0.1</sub>O<sub>3−δ</sub>, and 10H-BaCo<sub>0.9</sub>Ru<sub>0.1</sub>O<sub>3−δ</sub> with the same element\ncomposition but different [BaO<sub>3</sub>] layers via the sol–gel\nmethod. Here, 2H, 6H, and 10H refer to the number of [BaO<sub>3</sub>] layers contained in the unit cell of the BaCo<sub>0.9</sub>Ru<sub>0.1</sub>O<sub>3−δ</sub> system. Experimentally, 10H-BaCo<sub>0.9</sub>Ru<sub>0.1</sub>O<sub>3−δ</sub>, featuring\nten layers of [BaO<sub>3</sub>], exhibits optimal electrochemical\nactivity among the three oxide catalysts, and in situ Raman results\nunder various bias voltages confirm its ability to maintain a high\nsurface crystal structural stability. Notably, as the number of [BaO<sub>3</sub>] layers increases, the effective magnetic moments and the\nvalence state of surface Co ions in these three catalysts also increase,\nwith the spin configuration of the surface Co ions being in a high-spin\nstate. More importantly, DFT calculations provide the evolution rules\nof the p-band center (ε<sub>p</sub>) with the number of [BaO<sub>3</sub>] layers, predicting the electrochemical performance of the\nBaCo<sub>0.9</sub>Ru<sub>0.1</sub>O<sub>3−δ</sub> system\nwith different [BaO<sub>3</sub>] layers. Our experimental results\noffer a distinctive perspective for the future design, synthesis,\nand application of hexagonal perovskite oxides in electrocatalysis.