Simultaneous improvement of ionic conductivity and oxidative stability of sulfonated poly(ether ether ketone) nanocomposite proton exchange membrane for fuel cell application

Summary Simultaneous high proton conductivity with high oxidative stability is one of the major concerns in the proton exchange membrane (PEM) preparation. With this perspective, different loadings of the sulfated zirconia‐titania, a binary metal oxide that possesses enhanced physicochemical properties, nanoparticle in sulfonated poly(ether ether ketone) (SPEEK) polymer were evaluated by the response surface method to obtain the novel PEM with boosted proton conductivity and oxidative stability. Two models for correlation of proton conductivity and oxidative stability (in Fenton solution) with two independent factors, including sulfonation time and the weight percent of the nanoparticle loading, were obtained by central composite design. The optimum parameters to attain the highest proton conductivity with oxidative stability are found to be the sulfonation time of 6.48 hours and the nanoparticle weight percent of 10.12%. The nanoparticle loading was found to be the more significant factor in the proton conductivity model, while the sulfonation time in the oxidative stability model was the main affecting factor. The optimal membranes were characterized by 1H NMR, electrochemical impedance spectroscopy, Fenton test, Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), water uptake, swelling ratio, and atomic force microscopy (AFM) analysis. The results indicate that the introduction of the optimal contents of SZrTi nanoparticle into the polymer matrix would improve the water uptake and consequently the proton conductivity at a higher temperature while keeping the swelling ratio at an acceptable range. The highest achieved proton conductivity by the resulted nanocomposite was 29.21 mS cm−1 at 120°C with 186‐minute durability in the Fenton's reagent. Moreover, the maximum peak power density of 199 mW cm−2 was achieved at 90°C and 100% RH for the single‐cell performance test of nanocomposite‐based membrane electrode assembly (MEA), while it was recorded at 112 mW cm−2 for commercial MEA. Acceptable dispersion of SZrTi nanoparticle in the SPEEK matrix causes negligible fuel crossover flux (eg, 0.35 × 10−6 mmol s−1 cm−2 and 12.49 × 10−6 mmol s−1 cm−2 for nanocomposite‐based MEA and commercial MEA, respectively), which is indispensable to improve the mechanical and chemical stability. So, the novel prepared nanocomposite SPEEK‐based membrane would be a promising alternative for the Nafion membrane at moderate to high temperatures. Highlights Sul