Regulating Na Occupation to Introduce Non-Fermi-Liquid States of Na x CoO 2 for Enhanced Water Oxidation Activity.

The couplings among fundamental quantum parameters provide versatile freedom of manipulations for useful electronic structures, based on which optimized oxygen evolution reaction (OER) performances can be achieved. In this work, we demonstrate the successful regulation of the electronic structure in layered Na x CoO 2 oxides to introduce a non-Fermi-liquid (NFL) state by adjusting the Na content and Na occupation in the lattice. The presence of an NFL is facilitated by the weakened electron-electron correlation when the on-site Coulomb repulsion of Co 4+ with Na + and oxygen vacancy with Na + is balanced. As a feature of NFL, the metallic states in the vicinity of the Fermi energy contribute to a fast electron transfer efficiency and eventually to an improved OER performance. These findings open up a new avenue to design highly efficient OER electrocatalysts in strong electron-correlated transition metal material systems by consideration of couplings among the fundamental quantum parameters.