Effects of A-site Cations in Quadruple Perovskite Ruthenates on Oxygen Evolution Catalysis in Acidic Aqueous Solutions.

The quadruple perovskite ruthenate CaCu 3 Ru 4 O 12 is more active and stable than the benchmark catalyst RuO 2 in the oxygen evolution reaction (OER) in acidic aqueous solutions, where many oxide-based catalysts are dissolved. Studies on the crystal structures of quadruple perovskite ruthenates are rare, and the origin of OER activity or stability from a structural aspect has not been clarified in detail. This presents the need to study the effects of cations at the A site of quadruple perovskite ruthenates ACu 3 Ru 4 O 12 (A = Ca, Sr, La, Nd, and Ce) on the OER catalytic activity and stability in acidic aqueous solutions. CaCu 3 Ru 4 O 12 has the highest activity and stability among all quadruple perovskite samples. The type of cation at the A site changes the average Cu and Ru valence states, and the plot of OER activity versus the average Cu valence number shows a volcano-type relationship. In addition, stability increases with a decrease in Ru-O bond length. This research provides a good design principle for OER catalysts with high activity and stability in severely acidic aqueous solutions.