## 1 Introduction  
Among all of the electrochemical energy generators, proton exchange membrane fuel cells (PEMFCs) are one of the most promising technology for the clean, safe, and efficient generation of electric power [1]. Indeed, PEMFC has an energy to weight ratio ten times greater than lithium-ion batteries. This means that hydrogen powered vehicles have the potential to offer much greater range, while being lighter. In addition, while lithium batteries have a limited lifespan and need to be replaced [2], fuel cells do not degrade in the same way. They continue to produce energy as long as the fuel source is present, which can have significant environmental benefits over the normal working lifespan. The only exception is flow batteries, which have properties of both conventional batteries and fuel cells, but suffer from severe power and energy density limitations and typically require expensive and corrosive or toxic fluids to operate [3]. However, one of the challenges for the large-scale development of PEMFC devices is to increase the operating temperature of the cell from the current 70-90 \({}^{\circ}\)C to about 120 \({}^{\circ}\)C (DOE target [4]). This would allow for better kinetics of reactions at the electrodes, easier water management, and would thus reduce the complexity of the system and consequently reduce costs [5]. Surely, the crucial component of the cell, which strongly influences performance and cost, is the electrolytic membrane. The state of the art is based on a perfluorosulfonic acid ionomer, the most famous of which is Nafion\({}^{\oplus}\), produced by Dupont. Nafion has a hydrophobic Teflon-like backbone, which confers elevated chemical, thermal, and mechanical stability to the polymer, while the ion transport properties are guaranteed by the presence of hydrophilic long side sulfonic groups. In fact, the phase separation between these two hydrophobic and hydrophilic domains leads to the formation of channels for ion transportation [6, 7, 8]. However, disadvantages like the high cost (about 800 \(\$\)/m\({}^{2}\)), the high environmental impact particularly related to the synthesis of a perfluorinated polymer, the low ability to retain water over the 100 \({}^{\circ}\)C (required for the high temperature PEMFCs) [6], and the instability in a low hydration environment [9], must be considered. In this field, research focuses on new polymer electrolytes membranes with a good proton conductivity ability to maintain hydration at temperatures above 100 \({}^{\circ}\)C [10, 11]. The starting point is to develop new sulfonated polymers that are chemically and thermally stable, cheaper and at low impact, and with proton conductivity and cell performance comparable to Nafion, which can act as a suitable polymer matrix to design and synthesize innovative nanocomposite membranes [12, 13]. Good results were achieved on the sulfonated derivatives of poly (arylene ethers) [14], polysulfone [15], polyethersulfone [16], poly (arylene sulfide sulfone nitrile) [17], and poly (ether ether ketone) [18]. However, in most of the cases, the excessive swelling, which reduces the mechanical properties, and the relative low conductivity actually hampered the use of these membranes in PEMFCs applications [19]. Therefore, to overcome these drawbacks, the incorporation of an appropriate nanoadditive inside the polymer matrix is the main route to improve both proton conductivity and membrane strength [20, 21, 22, 23]. Generally, hygroscopic inorganic fillers, such as SiO\({}_{2}\), TiO\({}_{2}\), ZrO\({}_{2}\), phosphotnugic acid, or zeolite nanoparticles, would increase the water retention capacity and accordingly the proton conduction of the final composite membrane [24, 25, 26]. In the last few years, 2D- nanomaterials, such as nanoclays, layered double hydroxides (LDH), and graphene oxide, have been successfully used by [PERSON] and coworkers [16, 27].