Unusual double ligand holes as catalytic active sites in LiNiO(2)

Designing efficient catalyst for the oxygen evolution reaction (OER) is of importance for energy conversion devices. The anionic redox allows formation of O-O bonds and offers higher OER activity than the conventional metal sites. Here, we successfully prepare LiNiO(2) with a dominant 3d(8)L configuration (L is a hole at O 2p) under high oxygen pressure, and achieve a double ligand holes 3d(8)L(2) under OER since one electron removal occurs at O 2p orbitals for Ni(III) oxides. LiNiO(2) exhibits super-efficient OER activity among LiMO(2), RMO(3) (M = transition metal, R = rare earth) and other unary 3d catalysts. Multiple in situ/operando spectroscopies reveal Ni(III)→Ni(IV) transition together with Li-removal during OER. Our theory indicates that Ni(IV) (3d(8)L(2)) leads to direct O-O coupling between lattice oxygen and *O intermediates accelerating the OER activity. These findings highlight a new way to design the lattice oxygen redox with enough ligand holes created in OER process.