Mesoporous Silica-Enhanced Sulfonated Poly(Ether Ether Ketone)/Polyvinyl Alcohol Self-Healable Membrane for High Concentration Direct Methanol Fuel Cells

Abstract

Proton exchange membranes (PEMs) in direct methanol fuel cells (DMFCs) transport protons while minimizing fuel crossover. However, commercial Nafion membranes face durability and methanol permeability issues. This study introduces a novel self-healable mesoporous silica (MSN) modified sulfonated poly(ether ketone) (SPEEK)/polyvinyl alcohol (PVA) membrane to improve DMFC efficiency and longevity. The composite membrane comprising 3 wt% MSN (S/PVA/MSN3) shows proton conductivity comparable to the pristine SPEEK, despite the inclusion of non-conductive PVA. MSN's large specific surface area and high porosity enhance water retention and facilitate proton transport. The methanol permeability of S/PVA/MSN3 is reduced by 29% compared to the pristine SPEEK, attributed to the combined effect of PVA's superior selectivity for water over methanol and the tortuous pathways created by MSN. Thanks to its improved selectivity, a DMFC with S/PVA/MSN3 achieves a remarkable open-circuit voltage (OCV) of 0.63 V, even with a high methanol concentration of 8 M, and a peak power density of 8.79 mW cm⁻², which is 2.13 times greater than the commercial Nafion 117. Moreover, S/PVA/MSN3 demonstrates significant recoveries of 91% in OCV and 87% in maximum power output following damage and self-healing. These findings suggest that the self-healable S/PVA/MSN has the potential for future use in DMFCs.