Nickel-rich layered LiNi _1−xM _xO ₂(M = Mn, Fe, and Co) electrocatalysts with high oxygen evolution reaction activity

Abstract

The first systematic investigation of a family of Ni-rich layered lithium oxides reveals tunable catalytic activity.

Abstract

An understanding of the materials characteristics that lead to high electrocatalytic activity for the oxygen evolution reaction (OER) is needed to make electrolytic hydrogen fuel production and rechargeable metal-air batteries a reality. Here, the first systematic investigation of a family of Ni-rich layered LiNi _1−xM _xO ₂(M = Mn, Fe, and Co) oxides reveals that the catalytic activity can be tuned by varying the Ni content, nature of the transition-metal dopant, lithium content, and degree of cation ordering between Li and Ni/M. In particular, Fe-doping in LiNi _1−xM _xO ₂imparts the most dramatic improvements in OER activity, possibly due to the flexibility of Fe to adopt different coordination geometries on the surface. X-ray photoelectron spectroscopic (XPS) data reveal that the surface of the Fe-doped sample is enriched with Fe while ex situRaman spectroscopy indicates that the layered morphology is preserved during electrochemical cycling, but the cation disorder increases. Among the various LiNi _1−xM _xO ₂compositions investigated, LiNi _0.7Co _0.3Fe _0.2O ₂exhibits the highest OER activity, which increases further when excess lithium and oxygen vacancies are present, and good stability. The Ni-rich LiNi _1−xM _xO ₂samples join a growing number of highly active iron-doped systems for OER electrocatalysis in alkaline conditions.