Water-splitting electrocatalysis in acid conditions using ruthenate-iridate pyrochlores

Abstract

The pyrochlore solid solution (Na0.33Ce0.67)2(Ir1-xRux)2O7 (0≤x≤1) containing B-site RuIV and IrIV is prepared by hydrothermal synthesis and used as a catalyst layer for electrochemical oxygen evolution from water at pH<7. The materials have atomically mixed Ru and Ir and their nanocrystalline form allows effective fabrication of electrode coatings with improved charge densities over a typical (Ru,Ir)O2 catalyst. An insitu study of the catalyst layers using XANES spectroscopy at the Ir LIII and Ru Kedges shows that both Ru and Ir participate in redox chemistry at oxygen evolution conditions and that Ru is more active than Ir being oxidized by almost one oxidation state at maximum applied potential with no evidence for ruthenate or iridate in +6 or higher oxidation states. Ru/Ir cooperativity: A pyrochlore solid solution (Na0.33Ce0.67)2(Ir1-xRux)2O7 formed as nanocrystalline powder under hydrothermal conditions shows high activity for electrochemical oxygen evolution in aqueous acid. Insitu XAFS experiments show a cooperative effect of Ru and Ir that depends on the composition of the material. OER=oxygen evolution reaction.