Durable direct methanol fuel cells through cytosine-modified sulfonated poly(ether ether ketone) matrix with phosphorylated metal-organic framework integration

As the core component of proton exchange membrane fuel cells (PEMFCs), the PEM serves as a channel for proton transport and a barrier for electrodes, ensuring efficient energy conversion and the integrity of the cell performance. Metal-organic frameworks (MOFs), with their hybrid organic-inorganic lattices, embody a paradigm of structural and chemical versatility, offering a promising avenue for PEM material innovation. In this work, a phosphorylated MOF (ZnL) synthesized from 1, 1′-piperazinedimethylene phosphate and zinc chloride was integrated into a cytosine-modified SPEEK matrix, yielding advanced composite PEMs. The composite enhanced thermal stability, and mechanical integrity and minimized swelling of the membranes. The incorporation of ZnL improved the proton conductivity, enhanced thermal stability and decreased methanol permeability. The strong interaction between the nucleobase and phosphoric acid in the membrane stabilized the acid, ensuring the membranes' stability and increasing proton conductivity. All PA-doped membranes exhibited satisfactory proton conductivity and mechanical properties. Notably, the SPEEK-C-1ZnL/PA membrane achieved a decomposition temperature of 230 °C and a maximum proton conductivity of 240.34 mS cm −1 . During direct methanol fuel cell (DMFC) testing, it demonstrated a power density of 70.67 mW cm −2 and maintained an open circuit voltage of 90.6% after 320 h. These results highlight the potential of this membrane for DMFC applications.