A Sol-Gel Pretreatment Combined Strategy for Constructing Cobalt-Embedded and Nitrogen-Doped Carbon Matrix with High-Density Active Sites as Bifunctional Oxygen Reduction and Evolution Electrocatalysts

Abstract

Abstract Developing highly efficient bifunctional oxygen electrocatalysts via cost-effective methods is of great significance for energy storage and conversion systems but still full of challenges. In this work, a simple and eco-friendly method which involves a sol-gel pretreatment on multiple precursors and subsequent pyrolysis is designed to synthesize Co nanoparticles embedded and nitrogen-doped porous carbon (Co@NC). The sol-gel pretreatment ensures the high dispersion of all precursors, which is beneficial to the formation of uniform and highly dense active sites. After pyrolysis, acid treatment removes the unencapsulated Co nanoparticles on the surface to form porous structure and increase the mass activity. Benefiting from the synthetic strategy, the porous Co@NC-850 with large surface area, high density of active sites (graphitic N, pyridinic N and Co-Nx) exhibits comparable oxygen reduction performance (E1/2 =\xa00.85\xa0V vs. reversible hydrogen electrode) to that of commercial Pt/C and better oxygen evolution activity (with an overpotential of 350\xa0mV at 10\xa0mA\xa0cm−2) with respect to RuO2. The potential gap ΔE (between the oxygen evolution potential at 10\xa0mA\xa0cm−2 and oxygen reduction E1/2) for Co@NC-850 is only 0.73\xa0V. Compared with the state-of-the-art bifunctional oxygen electrocatalysts, Co@NC-850 shows obvious advantages in bifunctional activity and durability. The results in the present work will shed light on the development of other carbonaceous materials as the bifunctional oxygen electrocatalysts for energy storage and electrochemical devices.