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Proton exchange membranes (PEMs) with superior characteristics are needed to advance fuel cell technology. Nafion, the most used PEM in direct methanol fuel cells (DMFCs), has excellent proton conductivity but suffers from high methanol permeability and long-term performance degradation. Thus, this study aimed to create a healable PEM with improved durability and methanol barrier properties by combining sulfonated poly(ether ether ketone) (SPEEK) and poly-vinyl alcohol (PVA). The effect of changing the N,N-dimethylacetamide (DMAc) solvent concentration during membrane casting was investigated. Lower DMAc concentrations improved water absorption and, thus, membrane proton conductivity, but methanol permeability increased correspondingly. For the best trade-off between these two characteristics, the blend membrane with a 10 wt% DMAc solvent (SP10) exhibited the highest selectivity. SP10 also showed a remarkable self-healing capacity by regaining 88% of its pre-damage methanol-blocking efficiency. The ability to self-heal decreased with the increasing solvent concentration because of the increased crosslinking density and structure compactness, which reduced chain mobility. Optimizing the solvent concentration during membrane preparation is therefore an important factor in improving membrane performance in DMFCs. With its exceptional methanol barrier and self-healing characteristics, the pioneering SPEEK/PVA blend membrane may contribute to efficient and durable fuel cell systems. [ABSTRACT FROM AUTHOR]

Nafion, a perfluorosulfonic acid polymer, has been the standard membrane material for direct methanol fuel cells (DMFCs) due to its proton-carrying capabilities, despite its shortcomings as a methanol barrier. To attain self-healing and methanol-blocking properties, the incorporation of poly(vinyl alcohol) (PVA) polymer into Nafion was pursued. However, this strategy resulted in low proton conductivity. Thus, acid functional groups were added to a secondary modifier to boost proton conductivity. In this work, sulfonated graphene oxide (SGO) was assembled with Nafion and PVA through a simple freezing-thawing method to demonstrate a self-healable proton exchange membrane (PEM) without compromising the proton conductivity of Nafion. The synergistic effect of SGO in methanol-blocking and proton transport successfully strode over recast Nafion by hampering 33.2 % of methanol permeation and increasing 19.5 % of proton conductivity. As a result, the selectivity of the best hybrid PEM (N/PVA/SGO1.0) was increased by 1.8 times in comparison to recast Nafion. A single cell passive DMFC made using the novel hybrid membrane exhibited a power density of 6.07 mW cm−2 at a current density of 26.48 mA cm−2, and an open circuit voltage of 0.55 V at room temperature using 4 M methanol. This performance was essentially higher than that achieved by recast Nafion and commercial Nafion 117. The N/PVA/SGO1.0 hybrid membrane also showed remarkable self-healing properties, with 89 % recovery of methanol blocking function through reversible hydrogen bonding, illustrating its tremendous sustainable potential for use in DMFCs. [Display omitted] • Freeze-thaw process induces reversible physical crosslinking in N/PVA/SGO. • N/PVA/SGO achieves 28 % better DMFC performance than N117. • N/PVA/SGO demonstrates multiple times of self-healing. [ABSTRACT FROM AUTHOR]