Proton exchange membrane fuel cells (PEMFCs) have attracted extensive attention as a kind of alternative renewable energy converting devices due to their advantages of high energy and low/zero emissions [1]. At the current state of technology, carbon supported platinum catalysts have been recognized as the most practical catalysts for oxygen reduction reaction (ORR) in PEMFCs [2]. However, their catalytic performance including ORR activity and stability are still needed to further improve, and their cost has to be reduced in order to realize the real commercialization of PEMFCs [2-4]. In this article, one kind of ground ultrafine porous carbon fiber (UPCF) was used as a novel compound carbon support (CCS) to prepare supported Pt catalyst (Pt/CCS) for PEMFC electrode catalyst layer, and its associated membrane electrode assembly (MEA). The fabricated MEA was also tested in a single fuel cells to validate this Pt/CCS catalyst.

For the preparation of the ultrafine porous carbon fiber felts (UPCFFs), the first step was to synthesize the ultrafine blend fiber felts (UBFFs) [5, 6]. The UBFFs were prepared by electron-spinning of the polyacrylonitrile/polymethyl methacrylate (PAN/PMMA) blend with 70wt% of PAN using DMAc as the solvent. The obtained UBFFs were then carbonized to obtain the ultrafine porous carbon fiber felts (UPCFFs), which had an average diameter of the 100 nm, and the pore sizes of 5-30nm. The resultant UPCFF sample was ground into micrometer size and then used as the catalyst support by adding it into the 40wt% Pt/C catalyst solution to prepare carbon supported catalyst Pt catalyst with 20wt% of Pt, named as CCS-20 in this paper. The Pt/C catalyst with 20wt% of Pt purchased from Johnson Matthey was used as the baseline for comparison, named as JM-20.

The catalytic activities of the CCS-20 and the commercial catalyst JM-20 were screened by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) employing a rotating disk electrode (RDE). It was demonstrated sufficiently that the introduction of UPCFFs into the catalyst could efficiently enhance the catalytic ORR activity and utilization efficiency. The electrochemical surface area (ECSA) of Pt was determined to be 71.9m².g^-1 for CCS-20, which is much larger than that of JM-20. Thus, the enhanced Pt utilization efficiency was realized, from 54.5% for JM-20 up to 87.2% for CCS-20. Furthermore, in comparison with JM-20, both the onset potential and half-wave potential of CCS-20 were also positively shifted by 70mV and 20mV, reaching 964mV and 763mV, respectively.

The performance measurement a single PEMFC catalyzed by this CCS-20 catalyst shows that this CCS-20 catalyzed performance is much higher than that catalyzed by JM-20 in terms of power density. The results indicates that a maximum power density of 165.4mW.cm^-2 in CCS-20 case which is higher than 132.5mW.cm^-2 in JM-20 case at room temperature.

Presenter:Jian Song