High-Conductive CsH₂PO₄ Membranes with PVDF-Based Polymers Additives

The study is devoted to one of the important problems of hydrogen energy-the comparative analysis and creation of novel highly conductive and durable medium-temperature proton membranes based on cesium dihydrogen phosphate and fluoropolymers. The proton conductivity, structural characteristics and mechanical properties of (1 - x)CsH₂PO₄-x fluoropolymer electrolytes (x-mass fraction, x = 0-0.3) have been investigated and analyzed. UPTFE and PVDF-based polymers (F2M, F42, and SKF26) with high thermal stability and mechanical properties have been chosen as polymer additives. The used fluoropolymers are shown to be chemical inert matrices for CsH₂PO₄. According to the XRD data, a monoclinic CsH₂PO₄ (P2₁/m) phase was retained in all of the polymer electrolytes studied. Highly conductive and mechanically strong composite membranes with thicknesses of ~50-100 μm were obtained for the soluble fluoropolymers (F2M, F42, and SKF26). The size and shape of CsH₂PO₄ particles and their distribution have been shown to significantly affect proton conductivity and the mechanical properties of the membranes. The thin-film polymer systems with uniform distributions of salt particles (up to ~300 nm) were produced via the use of different methods. The best results were achieved via the pretreatment of the suspension in a bead mill. The ability of the membranes to resist plastic deformation increases with the growth of the polymer content in comparison with the pure CsH₂PO₄, and the values of the mechanical strength characteristics are comparable to the best low-temperature polymer membranes. The proton-conducting membranes (1 - x)CsH₂PO₄-x fluoropolymer with the optimal combination of the conductivity and mechanical and hydrophobic properties are promising for use in solid acid fuel cells and other medium-temperature electrochemical devices.