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

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.