Biomass-derived highly dispersed Co/Co9S8 nanoparticles encapsulated in S, N-co-doped hierarchically porous carbon as an efficient catalyst for hybrid Na–CO2 batteries

Na–CO2 batteries are prospective in energy storage and CO2 recycling applications; development of a high-efficiency, low-cost electrocatalyst to promote CO2 reduction and carbonate decomposition is extremely vital for practical Na–CO2 batteries. Herein, a highly efficient cathode catalyst for rechargeable hybrid Na–CO2 batteries is successfully synthesized by encapsulating highly dispersed Co/Co9S8 nanoparticles into carbon skeletons, consisting of biomass-derived S, N-co-doped hierarchically porous carbon (Co/Co9S8@SNHC). The conductive and hierarchically porous framework structure of the Co/Co9S8@SNHC can not only accelerate electron transport, electrolyte infiltration, and CO2 diffusion but also can inhibit overgrowth and agglomeration of Co/Co9S8 nanoparticles and expose numerous high density of active sites, as well as offer sufficient space to store discharge products. Benefiting from the synergistic effect among S and N dopants, carbon defects, and Co/Co9S8 nanoparticles in robust porous carbon structure, the hybrid Na–CO2 batteries displayed a low charge overpotential (only ~0.32 V) at 0.2 mA/cm2 and repeatedly charged and discharged over 200 cycles at 0.1 mA/cm2. Besides, an ultrahigh areal capacity of ~18.9 mAh/cm2 was obtained at 0.5 mA/cm2, the highest value to date for Na–CO2 batteries. Meanwhile, the hybrid Na–CO2 battery charging from Na2CO3@C catalytic cathode demonstrated the high catalytic activity of biomass-derived S,N-co-doped hierarchically porous carbon (Co/Co9S8@SNHC) for CO2 reduction and carbonate decomposition. Given this finding, this work might open up a potential avenue for the reasonable design of low-cost and highly efficient catalysts for advanced metal-CO2 batteries systems.