Enhanced Fe−N active site formation through interfacial energy control of precursor impregnation solution for the air cathode of membraneless direct formate fuel cells

In the development of platinum group metal-free (PGM-free) catalysts like carbon-based catalysts for oxygen reduction reaction (ORR), one of the key factors is increasing active site density to achieve highly catalytic activity. This work proposes a facile method to effectively increase the ORR active site density by controlling the interfacial energy between the carbon support and heteroatomic precursor (FePc)-containing solution during solvothermal treatment. Decreasing the interfacial energy by purposefully choosing solvents with proper surface tension promotes the delivery of FePc into intrinsic pores of the carbon support and enhances Fe and N doping, resulting in an increase of ORR active site density by triple to 6.84 × 10 18 sites g −1 . The high density of active site helps to achieve higher onset potential (0.937 V vs. RHE) and half-wave potential (0.895 V) than the benchmark Pt/C in a same catalyst loading in 0.1 M KOH, as well as a higher power output (16.1 ± 0.3 mW cm −2 ) when used for air cathode catalyst in a membraneless direct formate fuel cell. These findings provide insights into synthesis of highly active carbon-based catalysts with high active site density and broaden the development for fuel cell application.