Lattice Distortion Engineering: Manipulation of Electrochemical Properties for Pyrochlore Ruthenates as Electrocatalysts in Water Splitting

Pyrochlores ruthenates, owing to their D_3d symmetric configurations of [RuO₆] octahedra to efficiently avoid the Ru dissolution during the oxygen evolution reaction (OER) process, have been promising as non-iridium electrocatalysts for proton exchange membrane water electrolysis (PEMWE). In this work, a lattice-distortion strategy is proposed, by using a series of lanthanides (from Gd to Lu) as the dominant A sites and a series of alkalines (from Mg to Ba) as the A-site substitutions, to investigate the geometric effect on the pyrochlores for OER. It is found that the larger radii difference between the A sites and the A-site substitutions, the larger lattice expansion of these alloyed pyrochlore ruthenates, accompanied by the shortened Ru─O bonding, the enlarged Ru─O─Ru bond angle, and the enhanced covalency of [RuO₆] octahedra. The large lattice expansion also leads a rapid A-site leaching and the formation of protective RuO_x reconstruction layers, which suppress the progressive metal dissolution, the lattice contraction, and the resulting insulated OER deactivation. On account of the synergistic effect from the lattice distortion, the most distorted LuBa pyrochlores exhibit the highest OER performance and the greatest enhancement in either electrochemical testing or PEMWE operation, demonstrating their considerable potential for practical applications.