Crystal Growth, Structure, Magnetism, and Electrochemical Properties of Hexavalent Strontium Ruthenium Oxyhydroxide

We report the crystal growth and comprehensive studies including crystal and electronic structure and magnetic and electrochemical properties of the hexavalent ruthenium oxyhydroxide Sr₃Ru₂O₈(OH)₂ prepared through a low-temperature hydrothermal method. Single crystals and powder samples of this phase are isolated by optimizing the Sr-(OH)₂·8H₂O to KRuO₄ ratio while maintaining a high base concentration. The new structure consists of a rare five-coordinated Ru^VI featuring isolated trigonal prisms and crystallizing in a noncentrosymmetric tetragonal system. Isolated Ru polyhedra leading to a large spatial distance (∼5 Å) between the Ru metal centers render the compound paramagnetic despite strong antiferromagnetic correlation. Band structure calculation suggests a metal-like electronic ground state with mostly Ru d and O p orbitals contributing to the Fermi surface. The electrochemical performance of Sr₃Ru₂O₈(OH)₂, though not as impressive as that of RuO₂, remains relevant and is on par with other reported OER catalysts.