Single transition metal atom supported on NiOOH as highly efficient electrocatalyst for oxygen reduction and oxygen evolution reaction: A DFT study

Developing non-noble metal bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts with high activity and abundance is urgently needed. In this regard, the structures of 3d, 4d, and 5d transition metal (except Tc, Cd, and Hg) supported on NiOOH are constructed and studied by density func-tional theory calculations. Two sites on NiOOH support the single transition metal located at the top of the Ni or O atom in the substrate, namely TM-Ni@NiOOH or TM-O@NiOOH. According to the analysis of stability, 15 kinds of catalysts are not considered in the subsequent catalytic performance study due to poor stability and structural deformation. The calculated binding energy of the reaction species values on TM-Ni@NiOOH and TM-O@NiOOH indicate that Co-Ni@NiOOH, Ni-Ni@NiOOH, Fe-O@NiOOH, Co-O@NiOOH, and Ni-O@NiOOH exhibit appropriate binding strength of the reaction species. The Gibbs free energy analysis manifests that Ni-O@NiOOH is expected to be the promising bifunctional catalyst because it possesses low ORR/OER overpotentials with 0.45/0.55 V values. The potential determining step of the bifunctional catalyst Ni-O@NiOOH for ORR is the step of *OH reduction, while for OER is *O formation. At last, the calculated results of the deformation charge density and Mulliken charge manifest that the relatively strong interaction between reaction species and catalyst surface is due to their strong electron transfer. This work provides a perspective on TM atom supported on layered double hydroxides design for the ORR and OER processes.