B-site substituting strategy to boost the oxygen evolution reaction activity of hexagonal perovskite oxide 10H-BaCo0.9Ru0.1O3-δ

In this work, the electrocatalytic activity of hexagonal perovskite oxide 10H-BaCo 0.9 Ru 0.1 O 3-δ is improved by partially substituting the Co ions with Ti, Fe, and Nb ions, synthesizing BaCo 0.6 Ti 0.3 Ru 0.1 O 3-δ , BaCo 0.6 Fe 0.3 Ru 0.1 O 3-δ , and BaCo 0.6 Nb 0.3 Ru 0.1 O 3-δ , respectively. These three substituted samples preserve the original 10H-type hexagonal perovskite structure. Among them, BaCo 0.6 Fe 0.3 Ru 0.1 O 3-δ exhibits the lowest overpotential of 306 mV at 10 mA cm −2 geo , which is better than the pristine 10H-BaCo 0.9 Ru 0.1 O 3-δ (391 mV), BaCo 0.6 Ti 0.3 Ru 0.1 O 3-δ (418 mV), BaCo 0.6 Nb 0.3 Ru 0.1 O 3-δ (404 mV), and benchmark material RuO 2 (348 mV), mainly due to the Fe substitution increases in surface Co average oxidative state and enhances the proportion of surface OH − /O 2 species. Notably, Fe substitution induces a shift in the oxygen evolution reaction (OER) pathway from the adsorption evolution mechanism to the lattice oxygen participation mechanism, and BaCo 0.6 Fe 0.3 Ru 0.1 O 3-δ retains a stable surface structure without reconstruction under prolonged OER operation. Additionally, these three samples show paramagnetic characteristics at room temperature. Further inferred that the surface Co 3+ ions in Ti and Nb substituted samples maintain the high spin state consistent with the pristine 10H-BaCo 0.9 Ru 0.1 O 3-δ , but adopt a low spin state in the BaCo 0.6 Fe 0.3 Ru 0.1 O 3-δ . Our work demonstrates that the B-site substitution strategy effectively tunes the electronic environment of 10H-BaCo 0.9 Ru 0.1 O 3-δ , providing valuable insights for the rational design of high-performance hexagonal perovskite electrocatalysts. • 10H hexagonal perovskite enables B-site tuning of surface electronic and spin states. • Fe doping triggers the LOM pathway and preserves structural stability during OER. • Fe substitution shifts surface Co 3+ from high spin to low spin states.