When fabricating polymer nanocomposites (PNCs), it is difficult for nanoparticles to disperse stably in polymer matrix since their high‐surface energy can cause them to attract each other. In this paper, we review the effects of nanoparticle size, surface chemical properties, and thermodynamic parameters on the dispersion state of nanoparticles (including inorganic and organic particles) in PNCs and describe some key measures to promote the nanoparticles dispersion. The ideal nanoparticles dispersion in polymer melt is available when the particle size is smaller than the rotation radius of polymer chains and the particle surface is highly compatible or has interactions with the matrix. In polymer solution, establishing proper thermodynamic parameters is necessary to ensure the balance interactions among particles, solvents, and polymers, leading to the successful preparation of PNCs with ideal structure. These results could supply theoretical suggestions for the design of PNCs. Moreover, the equilibrium dispersion may be unavailable without reasonable kinetic parameters, even if the dispersion process is thermodynamically favorable. Therefore, more studies are required on both thermodynamics and kinetics of the dispersion process.

To achieve desirable performance of a polymer electrolyte membrane with higher proton conduction and better mechanical strength is a challenging work in the development of the phosphoric acid (PA) doped solid-state membrane for high temperature proton exchange membrane fuel cells. Firstly, phosphonated poly(2,6-dimethyl-1,4-phenylene oxide) (pPPO) was prepared by the bromination and phosphonation of poly(2,6-dimethyl-1,4-phenylene oxide). Afterward, a series of poly(vinyl pyrrolidone)–phosphonated poly(2,6-dimethyl-1,4-phenylene oxide) (PVP/pPPO) blend membranes and poly(vinyl pyrrolidone)–phosphonated poly(2,6-dimethyl-1,4-phenylene oxide)–graphitic carbon nitride (PVP/pPPO/g-C₃N₄) nanocomposite membranes were prepared by a solution casting method. The PA uptake, volume swelling ratio, and proton conductivity of the PVP/pPPO blend membrane increased with increasing PVP content. But PA molecules drastically reduced the mechanical strength of the PVP/pPPO blend membrane. The incorporation of g-C₃N₄ improved the proton conduction and mechanical properties of the nanocomposite membrane due to the proton hopped sites provided by NH₂ and the interaction of g-C₃N₄ and polymer chains. A higher proton conductivity of 74.4 mS cm⁻¹ and a higher power density of 294 mW cm⁻² at 180 °C without additional humidifying were observed for the PA doped PVP/pPPO nanocomposite membrane containing 5 wt% g-C₃N₄. The results show the PVP/pPPO nanocomposite membrane as a potential polymer electrolyte membrane for high temperature fuel cells.