Functionalized metallic transition metal dichalcogenide (TaS) 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-TaS 2 ). The PEMs are prepared through a solution-casting method and exploited in direct methanol fuel cells (DMFCs). Two-dimensional S-TaS 2 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-TaS 2 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-TaS 2 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 cm 2 s −1 , and a selectivity of 36.18 × 10 4 S s cm −3 . Moreover, SPEEK/S-TaS 2 membranes show superior thermal and chemical stabilities compared to those of pristine SPEEK. The DMFC fabricated with the SPEEK/S-TaS 2 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-TaS 2 membranes have a great potential for DMFC applications. Novel nanocomposite proton-exchange membranes based on sulfonated poly(ether ether ketone) (SPEEK) and functionalized tantalum disulfide (S-TaS 2 ) overcome the dichotomy of the properties of SPEEK membranes for direct methanol fuel cells.