Beschreibung:
While perfluorinated sulfonic acid (PFSA) membrane and ionomer materials such as Nafion® form the standard for high-performance proton-exchange membrane fuel cells (PEMFCs), the limited and difficult chemistry of perfluorinated materials hampers further material development to extended fuel cell performances and lifetimes, while the high cost of perfluorinated materials contributes to the cost barrier limiting the ubiquity adoption of fuel cells for energy generation. One method of reducing cost is the US Department of Energy target of 0.0625-0.125 mg PGM/cm2 as a catalyst loading. However, at low to ultra-low catalyst loadings, PFSAs exhibit a substantial increase in resistivity attributed to oxygen mass transport losses, particularly in the far Ohmic region of polarization data, causing disproportionate reductions to achievable power densities. Hydrocarbon proton-exchange materials offer the potential for solutions to material issues inherent to PFSAs, with established, varied chemistry allowing for versatile material innovation. Properties such as lower fuel crossover and improved operation in desirable operational conditions such as reduced relative humidity (RH) or high temperature has been well established. Together with the lower cost of basic materials and the ability to recycle catalyst layers, these properties make the demonstration of high performance, fully hydrocarbon PEMFC operation significantly of interest to the field. Here, hydrocarbon proton-exchange materials are shown that exhibit significant radical stability and high conductivities. Furthermore, these materials form thin membranes and are soluble in low-boiling, polar solvents necessary for incorporation as ionomer into catalyst inks that create high-quality catalyst layers. MEAs and catalyst layers were formed, incorporated into fuel cells, and characterized in situ by IV polarization, CV, CA, LSV, and EIS, and ex situ by mercury porosimetry and SEM. As ionomers, these exhibit reduced mass transport losses compared to PFSA ionomers, a result of substantially smaller increases to oxygen mass transport losses than PFSAs exhibit as catalyst layer loadings are decreased. As fully hydrocarbon fuel cells, improved interfaces lead to improved water transport and lower total resistivity attributable to membrane and ionomer congruency, thereby achieving higher power densities than directly comparable PFSA references using rigorously optimized conditions and catalyst loadings. These high-performance hydrocarbon proton-exchange materials may thereby represent a fully hydrocarbon alternative to PFSA materials for hydrogen fuel cells.