High-efficiency oxygen evolution catalysts: composite hexagonal structure SrCo_1−<i>y</i>Ni_<i>y</i>O_{3−<i>δ</i>}/Sr₉Ni₇O₂₁

Transition metal perovskite oxides are regarded as ideal catalysts for the oxygen evolution reaction (OER) owing to the high tunability of the B-site active elements. Among them, SrCoO₃ has been widely studied due to its high theoretical catalytic performance, but incomplete oxidation of the B-site elements results in poor intrinsic activity. Herein, we prepared a series of SrCo_1-<i>x</i>Ni_<i>x</i>O_3-<i>δ</i> (<i>x</i> = 0-0.5) catalysts for the alkaline OER using a simple sol-gel method and optimized their catalytic performance by modulating the Co/Ni ratio and annealing temperature (950 °C and 1050 °C). Among the series, SrCo_0.6Ni_0.4O_3-<i>δ</i> (annealed at 950 °C) with a composite hexagonal structure (SrCo_1-<i>y</i>Ni_<i>y</i>O_3-<i>δ</i>/Sr₉Ni₇O₂₁, <i>y</i> = 0.1-0.2) exhibited the best OER activity, achieving an overpotential of 321 mV at 10 mA cm^-2 (1 M KOH). The introduction of Ni ions and the presence of Sr₉Ni₇O₂₁ not only enhance the Co⁴⁺/Co³⁺ and Ni³⁺/Ni²⁺ ratios but also promote the generation of more highly oxidative oxygen species (O₂^2-/O^-). Additionally, the abundant Ni³⁺ surface facilitates the formation of a highly active NiOOH phase during the OER, leading to a further reduction in the overpotential (after 1000 CV cycles, the overpotential on the nickel foam electrode decreased by 45 mV).