Preparation Of Carbon-based Non-noble Metal ORR Catalysts And Study Of Their Performance

Using coffee grounds as the carbon source,a series of catalysts were prepared by co-pyrolyzing it with the mixture of iron and nitrogen precursors.The prepared catalysts were first characterized with XRD,SEM,BET,XPS,etc.,and then their electrocatalytic performance was studied.It was found that Fe2N active component was formed during the pyrolysis because of Fe in the precursor combining with the nitrogen inherent in the coffee grounds,that is,the nitrogen in the coffee grounds was utilized effectively.Furthermore,a high nitrogen-doped CGNFe-NH3 catalyst was prepared by further introducing a small amount of external nitrogen source and optimizing the calcination conditions,its half-wave potential reached 0.94 V in 0.1 M KOH and 0.78 V in 0.5 M H2SO4 electrolyte solution.This work opened a new pathway for the valueadded utilization of coffee wastes.An efficient S-doped Fe/N-C catalyst was synthesized via a simple method.The abundant C-S-C bonds formed in the sulfur-doped catalyst can effectively enhance the ORR activity,while the existence of excessive C-SOx-C bonds was unfavorable for the kinetics of the ORR.The existence of Fe was found to be able to increase both the contents of C-S-C bond and graphite N during the pyrolysis,thus generating more ORR active sites.The resulted effective configurations of S(C-S-C)and active N(both graphitic N and pyridinic N)and the combination of rich hierarchical porous structure with the encased Fe3C nanoparticles led to the excellent performance of catalysts.Particularly,the E1/2 of the FeNSC-10S reached 0.91 V in 0.1 M KOH electrolyte solution,which was 20 mV positive shift to the E1/2 of the 20 wt.%Pt/C commercial catalyst.The electron transfer number was determined to be 3.85-3.91 over the potential range of 0.4-0.8 V,indicating that the ORR catalytic process proceeded in a reaction pathway with nearly 4e-transfer.The developed catalyst also demonstrated a long-term stability as well as a superior methanol tolerance in alkaline conditions.