Effect of template size on the synthesis of mesoporous carbon spheres and their supported Fe-based ORR electrocatalysts

Three mesoporous carbon spheres (MPCs) are synthesized using three different templates with sizes of 22, 35 and 50 nm, respectively. These three MPC materials are then used as catalyst supports to form three catalysts (Fe-N-x/MPC22, Fe-N-x/MPC35, and Fe-N-x/MPC50) for oxygen reduction reaction (ORR). SEM images show that after catalyst deposition on the synthesized mesoporous carbon, the spherical morphology of mesoporous carbon is well maintained. EDX measurements show that the average Fe content in the formed mesoporous carbon supported catalysts is very close to the initial synthesis value of 5 wt%. BET and linear scanning voltammetry are used for characterizing the surface area and electrochemical properties of the synthesized MPC support materials to study the effect of template size (or pore size). The results show that mesoporous carbon with template size of 50 nm has the largest BET surface area (2125 m(2)/g). The measurement results show that all ORR activities of these three MPC supported catalysts are higher than that of commercially available carbon supported one, demonstrating the advantage of MPC support. Among these three catalysts, the performance order is Fe-N-x/MPC50 > FeNx/MPO5 > Fe-Nx/MPC22, showing the effect of template size on the ORR activity of the catalyst, i.e., the ORR activity increases when the template size (or MPC pore size) is increased. The results also clearly indicate that the mesopores in the range of 22-50 nm can still affect the ORR activity, suggesting that mesopores are also important in the formation of ORR active sites besides micropores. (C) 2013 Published by Elsevier Ltd.