LAUSR

Abstract A series of Co@N-C materials are synthesized from pyrolysis of ZIF-67 at different temperatures and employed as catalyst for electrochemical reduction of CO2 (CO2RR) to syngas. Through a systematical investigation of the relationship between structure of Co@N-C catalysts and their catalytic activity, it could be found that the Co species exposed on the material surface mainly promote the hydrogen evolution reaction (HER) process to produce H2, while the Co particles packaged by N-C skeleton provide electrons and transfer them to CO2 molecule through the Co-N-C skeleton, promoting the CO2 reduction reaction. Following this thinking, the pristine Co@N-C materials are treated by aqua regia to remove the surface exposed Co species. After acid treatment, the affinity of H species sharply decreases, and adsorption of CO2 and transfer of electron to CO2 are successfully improved. The acid-treated Co@N-C catalysts exhibit improved catalytic activity, faradic efficiency of CO, and stability in CO2RR process. Among all these catalysts, the obtained Co@N-C-700-A shows highest CO2 reduction activity and stability, achieving a specific current of 25 A∙g(cat)−1 and a productivity of 0.266 mol(CO) h−1∙g(cat)−1 at a mild potential of -0.57 V vs. RHE. The ratio of CO/H2 in products could be adjusted in the range of 1/4 to 1.5/1.