Transition Metal (Fe, Zn, Co, and Ni) Single-Atom Catalysts Anchored on N,S-Codoped Hybrid Nanocarbons for Oxygen Reduction Reaction

Atomically dispersed transition metal catalysts haveserved aspromising candidates to substitute noble metals in energy conversion.A majority of carbon-supported transition metal single-atom catalysts(SACs) have been synthesized via the high-temperature sintering method,in which the complex heating and cooling processes are time- and energy-consuming.Herein, we have developed a simple and highly effective microwave-assistedheating method to prepare a series of isolated transition metal SACsanchored on a N,S-codoped nanocarbon matrix, which are denoted asM-NSC-MW, M = Fe, Zn, Co, and Ni. Among the various M-NSC-MW, Fe-NSC-MWpossesses the highest ORR electrochemical activity in alkaline electrolytes.Its onset potential (E (onset)) is 0.955V, and its half-wave potential (E (1/2))can reach 0.852 V, both of which are the same as those of commercialPt/C. Moreover, Fe-NSC-MW also exhibits much superior ORR catalyticefficiency than conventional pyrolysis samples. It is worth notingthat Zn-NSC-MW is prepared for the first time, and it alsoshows a high ORR performance with an E (onset) of 0.945 V and an E (1/2) of 0.832 V. Thiswork has revealed the general application of the microwave-assistedheating method to prepare well-dispersed transition metal SACs anchoredon the N,S-codoped graphene/carbon hybrid matrix.