New Nanocomposites Derived from Cation-Nonstoichiometric Ba_x(Co, Fe, Zr, Y)O_3−δ as Efficient Electrocatalysts for Water Oxidation in Alkaline Solution

Perovskite oxides are promising electrocatalysts due to their rich composition, facile synthesis, and favorable stability under oxidizing conditions. Despite extensive research on doping strategies, the impact of cation nonstoichiometry on electrocatalytic performance is less understood. Here, we reveal that A-site cation nonstoichiometry significantly influences the phase evolution of Ba_x(Co, Fe, Zr, Y)O_3−δ, transitioning from a single cubic perovskite (x = 1) to a nanocomposite comprising a major cubic perovskite phase and a minor hexagonal swedenborgite phase (0.80 ≤ x ≤ 0.95). The nanocomposite with a nominal chemical composition of Ba_0.80Co_0.7Fe_0.1Zr_0.1Y_0.1O_3−δ showed markedly enhanced electrocatalytic performance for the oxygen evolution reaction (OER) in alkaline solutions due to the synergistic effect of the two strongly interacting phases, promoting a lattice-oxygen-participating OER pathway. Further optimizing cation nonstoichiometry allowed the design of nanocomposites with controlled phase concentrations. The optimal candidate, with an increased content of the swedenborgite phase, demonstrated further boosted OER performance.