Functionalized metallic transition metal dichalcogenide (TaS2) for nanocomposite membranes in direct methanol fuel cells

In this work, we designed a novel nanocomposite proton-exchange membrane (PEM) based on sulfonated poly(ether ether ketone) (SPEEK) and tantalum disulfide functionalized with terminal sulfonate groups (S-TaS₂). The PEMs are prepared through a solution-casting method and exploited in direct methanol fuel cells (DMFCs). Two-dimensional S-TaS₂ nanoflakes were prepared as a functional additive to produce the novel nanocomposite membrane for DMFCs due to their potential as a fuel barrier and an excellent proton conductor. To optimize the degree of sulfonation (DS) of SPEEK and the weight percentage (wt%) of S-TaS₂ nanoflakes in PEMs, we used the central composite design of the response surface method. The optimum PEM was obtained for SPEEK DS of 1.9% and a weight fraction (wt%) of S-TaS₂ nanoflakes of 70.2%. The optimized membrane shows a water uptake of 45.72%, a membrane swelling of 9.64%, a proton conductivity of 96.24 mS cm⁻¹, a methanol permeability of 2.66 × 10⁻⁷ cm² s⁻¹, and a selectivity of 36.18 × 10⁴ S s cm⁻³. Moreover, SPEEK/S-TaS₂ membranes show superior thermal and chemical stabilities compared to those of pristine SPEEK. The DMFC fabricated with the SPEEK/S-TaS₂ membrane has reached the maximum power densities of 64.55 mW cm⁻² and 161.18 mW cm⁻² at 30 °C and 80 °C, respectively, which are ∼78% higher than the values obtained with the pristine SPEEK membrane. Our results demonstrate that SPEEK/S-TaS₂ membranes have a great potential for DMFC applications.