MOF-driven ultrafine Co9S8 nanocrystals embedded in N, S-Codoped Multilayer-Assembled carbon nanoplates for efficient bifunctional oxygen electrocatalysis

To achieve broad commercialization of regenerative fuel cells and rechargeable metal-air batteries, the development of non-precious metal-based bifunctional oxygen electrocatalysts is critical. Herein, we report the controlled synthesis of MOF-derived ultrafine Co9S8 nanocrystals (similar to 6 nm) embedded in nitrogen-and sulfur- co-doped multilayer-assembled carbon nanoplates (Co9S8/NSCP) for highly efficient oxygen electrocatalysis through polymer self-assembly, metal-organic coordination, and subsequent space-confined pyrolysis. The resultant Co9S8/NSCP shows excellent catalytic activity towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with high half-wave potential (0.9 V) and low overpotential (370 mV), separately. The extremely low reversible oxygen overpotential of 0.7 V is achieved in 0.1 M KOH electrolyte, much better than those of single-component counterparts (Co9S8 or carbon), comparable or even superior to those of noble metal catalysts and recently reported advanced catalysts. The superior performance of Co9S8/NSCP can be attributed to the synergistic effect of highly exposed Co9S8 nanocrystals and heteroatom-enriched 3D carbon superstructure, enabling large surface area, protective graphitic layers, and abundant active sites towards fast catalytic kinetics and excellent durability. This work will open the door towards the rational construction of 3D carbon-based nanocrystals for a wide range of applications beyond catalysis.