Abstract
Electrochemical CO2 reduction to value-added chemicals is a critical and challenging process for research of sustainable energy. Herein, we synthesize new nickel single atom catalysts embedded in nitrogen doped hollow carbon spheres (Ni-N/C-x) via thermal treatment of Ni salts and nitrogen doped hollow carbon spheres (N/C-x). The state of Ni species on Ni-N/C-x can be tuned by the nitrogen species of N/C-x and pyrrolic-N favors the formation of atomic Ni species. Two catalysts, namely, Ni-N/C-1/4 contains more pyrrolic-N and more amount of atomic Ni species than that on Ni-N/C-3/2 have been prepared. During all the measurement potential range, Ni-N/C-1/4 displays a much higher catalytic activity for CO2 reduction to CO than Ni-N/C-3/2. Within the potential range of -0.63 V to -0.98 V versus reversible hydrogen electrode (RHE), the faradaic efficiencies of CO on Ni-N/C-1/4 exceed 70 %. Furthermore, Ni-N/C-1/4 exhibits high selectivity for CO and excellent stability during 4.5 h of CO2 reduction electrolysis at the potential of -0.78 V versus RHE.