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High-temperature proton exchange membrane fuel cells (PEMFCs) are becoming more appealing to researchers around the world due to several advantages such as high energy conversion efficiency, lightweight due to the use of polymeric materials, low noise due to the lack of mechanical components, zero or low emission of harmful greenhouse gases, simple design, first reaction kinetics, and simple water management. The performance, limitations, and possibilities for the practical implementation of different high-temperature proton exchange membranes (PEMs) utilized in fuel cells are discussed in this review paper. A suitable PEM must be developed to improve the performance of membrane electrode assemblies for high-temperature PEMFCs (working temperature above 100 °C). Various PEMs such as sulfonated poly(ether ether ketone) (SPEEK), sulfonated polystyrene (SPS), sulfonated polyimide (SPI), sulfonated polysulfone (SPSU), phosphoric acid doped polybenzimidazole (PA-PBI), perfluorosulfonic acid (PFSA) polymer-based membranes have been investigated as PEMs for fuel cell applications by several research groups. Among the various PEMs, PA-PBI membranes are the most promising high-temperature PEM for fuel cell applications because of their higher proton conductivity at high temperatures and anhydrous conditions, good chemical and thermal, mechanical stability, and high durability. However, the performance of high-temperature PEMs based on pristine PA-PBI is insufficient to fulfill the need for practical implementation of high-temperature PEMFCs, which needs to be enhanced further before they can be used commercially. Therefore, PA-PBI composite membranes containing various multifunctional inorganic, organic, and hybrid fillers are being actively explored to produce high-temperature PEMs. The PA-PBI composite membranes' proton conductivity increases with rising temperature and maintains conductivity in anhydrous conditions, as well as chemical, thermal, and oxidative stability under operating conditions and long-term performance stability. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • MD simulations and experimental studies were performed on PFSA/SGO composites. • SGO loading in PFSA polymer increased the mechanical characteristics and T g. • Strong antiplasticization effect of water was noted on PFSA/SGO composite membranes. • PFSA membranes loaded with SGO showed high proton conductivity. In this investigation, to understand the impact on glass transition temperature (T g) and increase the mechanical properties (elastic and shear modulus), proton conductivity, and single-cell performance, sulfonic acid (-SO 3 H) functionalized graphene oxide (SGO) was introduced in the perfluorosulfonic acid (PFSA) membranes (Nafion). We conducted atomistic molecular dynamics simulations of fully dry and hydrated PFSA membranes at various hydration levels and SGO loading. The T g of PFSA polymer composite membranes was increasing with the rising loading percentage of SGO because of the strong connection between the SGO and the PFSA polymer chains in the fully dry states. In addition, the strong antiplasticization effect of water resulted in a further increase of the T g of hydrated Nafion/SGO-4 composite membranes. The elastic and shear modulus of the Nafion/SGO (Nafion is trade name PFSA membranes) composites increased significantly with SGO loading because of the strong interfacial interaction between SGO and PFSA polymer chains. PFSA membranes loaded with SGO exhibited significant improvement in proton conductivity up to 0.167 S/cm at 90% relative humidity (RH), 95˚C, 2 wt% SGO loading, which is 1.51 times of recast Nafion membrane. In addition, PFSA composite membrane showed excellent fuel cell performance in terms of maximum power density up to 0.97 W/cm2 at 100% RH, 80 ˚C, 2 wt% SGO loading, which is ∼1.3 times of recast Nafion membrane at similar test conditions because of the hygroscopic nature of SGO, the creation of interconnected proton-conducting channels, and the reduction of fuel permeability through the prepared composite membranes. [ABSTRACT FROM AUTHOR]