Identifying the role of Ni and Fe in Ni-Fe co-doped orthorhombic CoSe2 for driving enhanced electrocatalytic activity for oxygen evolution reaction

Exploring the origin of high electrocatalytic activity of Ni-Fe-Co ternary selenides for oxygen evolution reaction (OER) is of fundamental importance for rational design of efficient electrocatalysts. In this report, we synthesize self-assembled microspheres by orthorhombic CoSe2 nanorods along with the Ni and/or Fe doped counterparts, and systematically investigate their electrocatalytic performance. The results show that, although either Ni-doping or Fe-doping can significantly enhance the catalytic activity of CoSe2, the ways they promote catalytic activity are different. The Tafel analysis demonstrates that Fe incorporation leads to a kinetics change in the OER while Ni incorporation has little effect. Based on the electrochemical characterizations and theoretical calculations, Ni-doping maintains Co active sites and does not alter the OER mechanism, but decreases the energy barrier of the rate-limiting step by modifying Co active sites. In contrast, Fe-doping transforms the active sites from Co to Fe, and the rate-limiting step changes to the O-OH formation stage, thus affording faster reaction kinetics. These findings are further confirmed by more Ni-Fe co-doped CoSe2 with various content of Ni and Fe. Specifically, under the optimal experimental conditions, Ni-Fe co-doped CoSe2 (Ni0.04Fe0.16Co0.8Se2) exhibits a remarkable OER activity with an overpotential of similar to 230 mV at 10 mA cm(-2) and Tafel slope of 39 mV dec(-1). (C) 2020 Elsevier Ltd. All rights reserved.