Triple phase boundary augmentation in hierarchical, Pt grafted N-doped mesoporous carbon nanofibers for high performance and durable PEM fuel cells†
Pt-grafted, hierarchical mesoporous carbon nanofibers (Pt/MPCNFs) electrocatalysts have been developed using electrospinning for high-performance PEM fuel cells. The morphological analysis of Pt/MPCNFs revealed uniformly dispersed Pt nanoparticles (2–3 nm) strongly grafted onto the hierarchical nanochannels of mesoporous carbon nanofibers (MPCNFs). Pyridinic and pyrrolic nitrogen species formed in the sp2 graphitic structure during the carbonization process of the MPCNFs have been found to play a major role in augmentation of the triple phase boundaries in the catalyst support materials. Pt/MPCNFs exhibited outstanding electrocatalytic performance towards the oxygen reduction reaction (ORR) with a positively shifted onset potential (54 mV), half-wave potential (78 mV) and high limiting current density (4.75 mA cm−2 at 0.4 V) compared to state-of-the-art Pt/C electrocatalysts in acidic medium and they exhibited superior long-term stability (89.8% retention after 30 000 s and less change in activity after 10 000 potential sweeps). Pt/MPCNFs as a cathode catalyst yielded a maximum power density of 428.6 mW cm−2 during single cell testing, which is 2.08 times higher than a commercial Pt/C electrocatalyst. The electrochemical performance evaluation clearly implied that the unique combination of ultrathin nanofibers with a three-dimensional mesoporous structure, high electrical conductivity, enhanced specific surface area, homogeneous dispersion of Pt nanocatalysts and the presence of optimal nitrogen doping offers superior electrocatalytic activity via a favorable four-electron pathway and long-term operating stability during repeated cycles. Performance analysis in a single PEM fuel cell shows twice the power density (428 mW cm−2) with Pt/MPCNFs compared to commercial electrocatalyst membranes due to the effective enhancement in the triple phase boundaries, indicating that Pt/MPCNFs are potential candidates for high-performance, durable PEMFCs.