CsH₅(PO₄)₂ doped glass membranes for intermediate temperature fuel cells

This study reports the preparation of glass membranes doped with CsH₅(PO₄)₂ by an optimized sol - gel method using phosphoric acid as a catalyst for tetraethylorthosilicate (TEOS) hydrolysis and the application of these membranes in intermediate temperature fuel cells (ITFCs). Infrared spectroscopy shows the formation of Si - O - P bonds and scanning electron microscopy shows that the glass membranes have smooth cross-sectional structures. Domains of CsH₅(PO₄)₂ with sizes of 5-12 nm are uniformly distributed over the membrane cross section. The melting point of CsH₅(PO₄)₂ in the glass membrane is lower by 20-40°C than that for pure CsH₅(PO₄)₂. For a glass membrane with a molar ratio of SiO₂:CsH₅(PO₄)₂:H₃PO₄ = 4:1:0.36, 62% of the pore volume is filled with CsH₅(PO₄)₂ and shows the best electrochemical performance. The glass membrane shows high conductivity of 22 mS cm^-1 at 219°C. The membrane is novel because the silica support forms an interconnected matrix that provides stability, as shown by continuous operation at 210°C for at least 50 h. A fuel cell assembled with the glass membrane exhibits an open circuit voltage of 0.94 V and a peak power density of 85 mW cm^-2. The fuel cell produces a stable output voltage of 0.53 V for at least 50 h under a current density of 100 mA cm^-2.