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.