High performance tetra-sulfonated poly(p-phenylene-co-aryl ether ketone) membranes with microblock moieties for passive direct methanol fuel cells

A series of tetra-sulfonated poly(p-phenylene-co-aryl ether ketone) membranes (l-tSPP-co-PAEK x) with microblock moieties have been synthesized by nickel (0) catalytic coupling copolymerization and show good dimensional stability. Compared with the mono-sulfonated poly(p-phenylene-co-aryl ether ketone) membranes (SPP-co-PAEKs), the relationships between water content, the state of water molecules, proton conductivity, methanol permeability, and morphology for the membranes are detailedly investigated. Analyses by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) show that the l-tSPP-co-PAEK x greatly facilitated the connected proton transport channel. The proton conductivity of l-tSPP-co-PAEK x membrane is up to 60.0 mS cm(-1) at room temperature, which is 32% higher than that of the proton conduction in SPP-co-PAEKs, despite the IEC values are lower than that of the latter. The membranes exhibit high power densities in the range of 27.5-31.9 mW cm(-2) for passive direct methanol fuel cells (DMFCs) at room temperature. The power density of l-SPP-co-PAEKs 1.20 is higher than that of commercial Nation 115 (29.3 mW cm(-2)) and Nafion 117 (24.3 mW cm(-2)) under same test conditions. The desirable properties of l-tSPP-co-PAEK x membranes can be attributed to the synchronous introduction of locally and densely sulfonated hydrophilic units and hydrophobic microblock moieties in the membrane structure, resulting in the formation of the connected proton transport channel. (C) 2016 Elsevier B.V. All rights reserved.