High methanol tolerant proton exchange membranes based on novel coupling-type sulfonated poly(phenylquinoxaline) for direct methanol fuel cells

Coupling-type sulfonated poly(phenylquinoxaline) (c-SPPQ) bearing both side chain and main chain sulfonic acid groups were synthesized through the post-sulfonation process. The proton exchange membranes prepared with c-SPPQ showed good performance, such as low methanol permeability, high methanol tolerance and good mechanical properties due to the acid-base interaction between the sulfonic acid and phenylquinoxaline groups. The dimensional change of c-SPPQ-3 in the length direction was 33% at 30 °C in 45 wt% methanol solution, demonstrating the stability of membrane electrode assembly against shearing force. In contrast, NR212experienced significant swelling. The methanol flux of c-SPPQ-3 was 45 mg cm−2 h−1 for at 30 °C with a methonal concentration of 10 wt%. This was almost 10 times lower than that of NR212. With a 20 wt% methanol feed concentration at 75 °C, the maximum power density of c-SPPQ-3 was 88 mW cm−2, 1.8 times higher than that for NR212 (48 mW cm−2). This was attributed to the reasonably high proton conductivity and low methanol permeability of c-SPPQ-3. When the methanol feed concentration was further increased to 50 wt%, the maximum power density of c-SPPQ-3 slightly decreased to 60 mW cm−2, while that of NR212 was negligible. With such superior performance, c-SPPQ shows excellent promise for meeting the requirements of direct methanol fuel cells. [Display omitted] •A novel composite-type sulfonated poly(phenylquinoxaline) with sulfonic acid groups introduced in the side chain and main chain are designed and prepared.•Low methanol permeability and improved methanol tolerance is due to interaction between sulfonic acid and phenylquinoxaline.•PEM with high proton conductivity because of the modification is prepared.