Understanding of hydrocarbon ionomers in catalyst layers for enhancing the performance and durability of proton exchange membrane fuel cells

Abstract

Sulfonated hydrocarbon polymers have been widely investigated as proton exchange membranes (PEM) for application in proton exchange membrane fuel cells (PEMFC). However, there is very little reports on their incorporation as ionomers in catalyst layers for hydrocarbon-based PEMFC. Hence, three kinds of hydrocarbon ionomers are prepared and incorporated into alcohol-based catalyst inks to manufacture the catalyst-coated membranes. Especially, sulfonated poly(arylene ether ketone) with symmetric tetramethyl groups (SPAEK-TM) demonstrates superior performance and durability as ionomer in catalyst layers. SPAEK-TM-based membrane electrode assembly (SPAEK-TM-MEA) shows not only excellent catalyst layer morphology, but also outstanding active electrochemical surface area (50.36 m2 gPt−1). SPAEK-TM-MEA also exhibits a superior power density, which is 92 mW cm−2 in direct methanol fuel cell (DMFC) and 514 mW cm−2 in H2/air PEMFC. After 3000 degradation cycles, there is only 8.56% loss of the maximum power density for SPAEK-TM-MEA in H2/air PEMFC, which is lower than the loss of Nafion-MEA (14.6%). Furthermore, the incorporation of SPAEK-TM ionomer can effectively inhibit methanol permeability in DMFC. These results illustrate that hydrocarbon ionomer not only displays the superior power density, but also exhibits an excellent durability than Nafion® ionomer for hydrocarbon PEM-based MEA for PEMFCs.