Electrocatalytic Activity of Core-shell Carbon-metal Nanocomposites Derived From Carbon Dioxide

摘要

The polymer electrolyte fuel cell (PEFC) is one of promising devices to convert chemical energy of fuels to electrical energy with high energy efficiency, high power density, and low environment impact. Despite wide applications in many areas, the large-scale commercialization of PEFCs is difficult because of the high cost of platinum-based electrocatalysts for oxygen reduction reaction (ORR) at cathode. There have been numerous efforts to developing alternative materials to platinum-based electrocatalysts and here we introduce boron-doped carbon/iron nanocomposites (Fe/B/C) as oxygen reduction electrocatalysts. They were synthesized through the reduction of CO_2 by NaBH_4 with a Fe precursor at 500 °C and atmospheric pressure. Furthermore we performed heat treatments of the resulting Fe/B/C at 850 °C, 1050 °C (sample named as FeBC050, FeBC850 and FeBC105). Fe/B/C composites have a core@shell structure, in which the iron-containing nanoparticles are confined within onion-like graphitic carbon shells. Electrochemical analyses in cyclic voltammetry (CV) and rotating disk electrode (RDE) showed Fe/B/C composites enhanced ORR activity and especially FeBC105 presented excellent performance. Through XRD analyses, XPS, SEM and HRTEM observations, the thermal annealing is proved to be the reason for this better performance that changes the surface state and more active sites are generated by both the reduction of γ-Fe_2O_3 and the decomposition of B_4C species.