Mesoporous carbons supported non-noble metal Fe-NX electrocatalysts for PEM Fuel Cell oxygen reduction reaction

Three types of iron-nitrogen containing non-noble metal catalysts, supported on an ultrasonic spray pyrolysis mesoporous carbon (USPMC), a hollow core mesoporous shell carbon (HCMSC), and a standard carbon (Ketjen Black CJ600, KB), respectively, are synthesized using a wet-impregnation method. The morphologies and structure as well as composition of the synthesized carbon supports and their corresponding supported Fe-NX catalysts (namely Fe-NX/USPMC, Fe-NX/HCMSC, and Fe-NX/KB, respectively) are physically characterized using EDX, SEM, FESEM, and BET analysis, respectively. The catalytic activities of these three electrocatalysts towards oxygen reduction reaction (ORR) are measured using rotating disk electrode technique in O2-saturated 0.5 M H2SO4 solution. The catalyzed ORR exchange current densities are also obtained using the Tafel method based on the measured data. Among these three electrocatalysts, Fe-NX/HCMSC can give the best ORR performance, which is correlated to its higher nitrogen, mesopore and micropore contents. It is rationalized that the performance improvement of these electrocatalysts may be achieved as long as an optimal relationship among mesopores, micropores, and even macropores for increasing both ORR kinetics and reactant gases accessibility to the active sites can be found