Template-free synthesis of novel hollow carbon nanospheres with dual active sites as catalyst for fuel cell cathode to improve oxygen reduction reaction performances

A new template-free controlled method is reported herein to prepare the novel hollow carbon nanospheres with dual active sites of FeN4 and FeC3 by in situ growth reaction on graphene nanosheets, labeled as HCN-FNFCG. As-prepared HCN-FNFCG nanomaterials possess hierarchically porous FeN4/FeC3 shells with structures of microporous, mesoporous, and macroporous properties. Moreover, the hierarchically porous HCN-FNFCG nanomaterials with dual active sites of FeN4 and FeC3 have not been reported before. The HCN-FNFCG nanomaterials, as oxygen reduction reaction (ORR) catalysts, are first studied systematically toward cathodic ORR of fuel cell. The measurements have illustrated that HCN-FNFCG-650 has the best ORR performances among these HCN-FNFCG nanomaterials studied. The onset potential of HCN-FNFCG-650 has reached 1.095 V in alkaline electrolyte, and its maximum current density is 6.48 mA cm(-2). Additionally, the HCN-FNFCG-650 has also displayed small electrochemical impedance, its Tafel-slope value is 44.25 mV dec(-1), much lower than that of the 20% Pt/C (69.57 mV dec(-1)). And its value of current density is still maintained 92.83% of the initial value after 9000-second continuous tests. High tolerance against methanol crossover is also exhibited for HCN-FNFCG-650. This novel method of template-free synthesis can provide a promising strategy for preparing hollow nanospheres with hierarchically porous shells. And it can be used to design ORR electrocatalysts, electrode materials, or other applications.