Boosting Water Splitting\nvia Metal–Support\nRedox Interaction in Ce<sub>1–<i>x</i></sub>M<sub><i>x</i></sub>O<sub>2−δ</sub> (M = Co, Ni,\nCu)

The efficiency of electrochemical water splitting is\nconstrained\nby the anodic oxygen evolution reaction (OER), which suffers from\nhigh energy barriers, sluggish kinetics, and significant overpotential.\nDesigning affordable and efficient electrocatalysts for the OER remains\na key goal for advancing the hydrogen economy, with transitional metals\nlike Co, Ni, and Cu gaining significant attention as promising alternatives\ndue to their redox properties, abundance, and economy. The oxidation\nstep of M<sup>n+</sup> → M<sup>(n+1)+</sup> (M = Co, Ni, Cu)\nis the key intermediate step that produces the active species (M-OOH)\nformation, and thereby lowers the energy barrier and enhances the\nkinetics of the OER. However, the oxidation of M<sup>n+</sup> →\nM<sup>(n+1)+</sup> creates charge-transfer orbitals near the Fermi\nenergy level, which is fundamentally challenging. In this study, through\nstructural and surface analyses, we demonstrate that the highly reducible\nCeO<sub>2</sub> support in the Ce<sub>1–<i>x</i></sub>M<sub><i>x</i></sub>O<sub>2−δ</sub> solid-solution\neffectively facilitates the M<sup>n+</sup> → M<sup>(n+1)+</sup> oxidation process and the evolution of lattice oxygen during the\nOER. Among the three transition metals, the presence of the Ni<sup>3+</sup> species along with the surface oxygen vacancy promoted the\nformation of -OOH surface intermediates and maximized the OER activity\nin Ce<sub>0.95</sub>Ni<sub>0.05</sub>O<sub>2−δ</sub> catalyst.