High-Valence W6+ Ions Boost Cr2+ Activity in CrWO4 for Ideal Water Oxidation.

ABSTRACT

Electrocatalytic activity of multi-valence metal oxides for oxygen evolution reaction (OER) arises from various interactions among the constituent metal elements. Although the high-valence metal ions attract recent attentions due to the interactions with their neighboring 3d transition metal catalytic center, atomic-scale explanations for the catalytic efficiencies are still lacking. Here, by employing density functional theory predictions and experimental verifications, unprecedented electronic isolation of the catalytic 3d center (M2+) induced by the surrounding high-valence ions such as W6+ is discovered in multivalent oxides MWO4 (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn). Due to W6+'s extremely high oxidation state with the minimum electron occupations (d0), the surrounding W6+ blocks electron transfer toward the catalytic M2+ ions and completely isolates the ions electronically. Now, the isolated M2+ ions solely perform OER without any assistant electron flow from the adjacent metal ions, and thus the original strong binding energies of Cr with OER intermediates are effectively moderated. Through exploiting "electron isolators" such as W6+ surrounding the catalytic ion, exploring can be done beyond the conventional materials such as Ni- or Co-oxides into new candidate groups such as Cr and Mn on the left side of the periodic table for ideal OER.