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

The quadruple perovskite ruthenate CaCu3Ru4O12 is more active and stable than the benchmark catalyst RuO2 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. CaCu3Ru4O12 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.