Unusual double ligand holes as catalytic active sites in LiNiO2

Lattice-oxygen redox is pivotal for high oxygen evolution reaction (OER) activity. Here, LiNiO2, a unary 3d-transition metal oxide catalyst, exhibits superefficient activity during the OER due to the creation of double O 2p holes states, according to operando XAS, XRD, and Raman spectroscopy observations. 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 LiNiO2 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. LiNiO2 exhibits super-efficient OER activity among LiMO2, RMO3 (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.

Automated summary

LiNiO2 catalyst exhibits super-efficient activity during the oxygen evolution reaction (OER) due to the formation of double O 2p holes states, as observed by operando XAS, XRD, and Raman spectroscopy. Designing efficient OER catalysts is crucial for energy conversion devices.