Designing fuel cell catalyst support for superior catalytic activity and low mass-transport resistance

Abstract

The development of low-Platinum content polymer electrolyte fuel cells (PEFCs) has been hindered by inexplicable reduction of oxygen reduction reaction (ORR) activity and unexpected O2 mass transport resistance when catalysts have been interfaced with ionomer in a cathode catalyst layer. In this study, we introduce a bottom-up designed spherical carbon support with intrinsic Nitrogen-doping that permits uniform dispersion of Pt catalyst, which reproducibly exhibits high ORR mass activity of 638 ± 68 mA mgPt−1 at 0.9 V and 100% relative humidity (RH) in a membrane electrode assembly. The uniformly distributed Nitrogen-functional surface groups on the carbon support surface promote high ionomer coverage directly evidenced by high-resolution electron microscopy and nearly humidity-independent double layer capacitance. The hydrophilic nature of the carbon surface appears to ensure high activity and performance for operation over a broad range of RH. The paradigm challenging large carbon support (~135 nm) combined with favourable ionomer film structure, hypothesized recently to arise from the interactions of an ionic moiety of the ionomer and Nitrogen-functional group of the catalyst support, results in an unprecedented low local oxygen transport resistance (5.0 s cm−1) for ultra-low Pt loading (34 ± 2 μgPt cm−2) catalyst layer.

Interfacial Distribution of Nafion Ionomer Thin Films on Nitrogen-Modified Carbon Surfaces

“…Moreover, the values corresponding to Films N200–N600 indicated that the oxygen concentration decreased and the nitrogen concentration increased with increasing NH 3 treatment temperature. These findings suggest that the NH 3 treatment replaced the O functional groups with N functional groups. − …”

“…The effects of the carbon–ionomer interactions on the catalyst layer are discussed henceforth. The rigid ionomer bonding on the N-modified carbon supports presumably suppresses the ionomer poisoning of Pt catalysts in the catalyst layer, resulting in improved PEFC performance upon the use of the N-modified carbon supports in the cathode catalyst layers. − Furthermore, N-modified carbon supports can reduce the amount of “nonadsorbed ionomers” in catalyst inks, which adversely affects the dispersion stability, viscosity-related properties, − and the quality of the catalyst layer, emphasizing their potential role in ensuring productivity and durability of PEFCs.…”

“…The introduction of nitrogen to the surface of carbon supports has been proposed as an approach to distribute ionomers throughout the catalyst uniformly and thereby prevent ionomer poisoning and the formation of a dense ionomer layer at the Pt–ionomer interface. − This approach is fascinating because it involves the use of low-cost conventional materials. Orfanidi et al claimed that carbon supports modified by NH 3 treatment to have −NH x groups on their surface achieved a uniform ionomer distribution via Coulombic interactions with the negatively charged ionomer side chains (SO 3 – ).…”

Towards ultralow platinum loading proton exchange membrane fuel cells

“…49,50 Moreover, the ultralow Pt loading (0.034 mg Pt cm À2 ) MEA with Ndoped carbon support developed by Islam et al even demonstrated less than half of pressure-independent oxygen transport resistance than the high Pt loading (0.063 mg Pt cm À2 ) MEA without that. 51…”

Manipulating the interaction of Pt NPs with N-hollow carbon spheres by F-doping for boosting oxygen reduction/methanol oxidation reactions

“…14 More importantly, Pt-based nanoparticles (NPs) are prone to migrate and agglomerate during long-term operation, which further leads to a decrease in catalytic activity and durability. [15][16][17] To address the above-mentioned barriers, the utilization of Pt atoms can be improved by regulating the size, morphology and interaction with the support of Pt NPs, thereby improving its electrocatalytic activity and antipoisoning ability.…”