Bifunctional catalyst of well-dispersed RuO2 on NiCo2O4 nanosheets as enhanced cathode for lithium-oxygen batteries

Abstract

The electrochemical properties of Li–O2 batteries are mainly restricted by the kinetics of the OER (oxygen evolution reaction) before realizing high-rate and long-term cycling performance. Among various excellent OER catalysts, RuO2 has shown excellent catalytic activity and good electrical conductivity. Here, a bifunctional catalyst with RuO2 well dispersed on NiCo2O4 nanosheets has been studied, showing a low OER Tafel slope of as low as 58 mV/decade in alkaline media. While assembled in Li–O2 batteries with RuO2@NiCo2O4 cathode, a large specific discharge capacity as high as 17,633 mAh g−1 can be obtained at a current density of 200 mA g−1 with a coulombic efficiency of 91%. A long-term stability about 128 cycles can be achieved without much deterioration. The excellent electrochemical performance is strongly correlated with the nanosheets like structure for easy O2 diffusion, electrolyte permeation, sufficient space provision of Li2O2 deposition and cooperation of NiCo2O4 and RuO2, which exhibits excellent ORR (oxygen reduction reaction) and OER catalytic activity respectively.