Oxide perovskites
have attracted great interest as materials for
energy conversion due to their stability and structural tunability.
La-based perovskites of 3d-transition metals have demonstrated excellent
activities as electrocatalysts in water oxidation. Herein, we report
the synthesis route to La-based perovskites using an environmentally
friendly deep eutectic solvent (DES) consisting of choline chloride
and malonic acid. The DES route affords phase-pure crystalline materials
on a gram scale and results in perovskites with high electrocatalytic
activity for oxygen evolution reaction. A convenient, fast, and scalable
synthesis proceeds via assisted metathesis at a lower temperature
as compared to traditional solid-state methods. Among LaCoO3, LaMn0.5Ni0.5O3, and LaMnO3 perovskites prepared via the DES route, LaCoO3 was established to be the best-performing electrocatalyst for water
oxidation in alkaline medium at 0.25 mg cm–2 mass
loading. LaCoO3 exhibits current densities of 10, 50, and
100 mA cm–2 at respective overpotentials of approximately
390, 430, and 470 mV, respectively, and features a Tafel slope of
55.8 mV dec–1. The high activity of LaCoO3 as compared to the other prepared perovskites is attributed to the
high concentration of oxygen vacancies in the LaCoO3 lattice,
as observed by high-resolution transmission electron microscopy. An
intrinsically high concentration of O vacancies in the LaCoO3 synthesized via the DES route is ascribed to the reducing atmosphere
attained upon thermal decomposition of the DES components. These findings
will contribute to the preparation of highly active perovskites for
various energy applications.