Synthesis, characterization and electrochemical properties of SiO2–P2O5–TiO2–ZrO2 glass membranes as proton conducting electrolyte for low-temperature H2/O2 fuel cells

Abstract

In this paper, we report on the phosphosilicate glass membranes doped with a mixture of titanium oxide (TiO2) and zirconium oxide (ZrO2) for their applicability in low-temperature H2/O2 fuel cell electrolytes. Measurements concerning x-ray diffraction, optical absorption/transmission, Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric and differential thermal analysis, impedance and permeability studies as well as electrochemical analysis were carried out. The specific surface area and pore size distributions were described by the Brunauer–Emmett–Teller method and the average pore size found to be approximately in the range 2.1–2.3 nm for all composite membranes. The FTIR analysis displayed a maximum intensity in the range 1000–1300 cm−1, indicating the presence of Si–O–Si bonds in all the studied composite glass membranes. A high proton conductivity of 9.3 × 10−3 S cm−1 was obtained for the 83SiO2–5P2O5–2TiO2/10ZrO2 (mol%) composite at 80 °C under 90%RH, while for the 83SiO2–5P2O5–2ZrO2/10TiO2 (mol%) composite the conductivity was only 7.1 × 10−3 S cm−1 under the same conditions. The permeability was measured for a hydrogen flow background and was found to decrease from 1.77 × 10−11 to 5.95 × 10−12 mol cm−1 s−1 Pa−1 for 2TiO2/10ZrO2 (mol%) doped glass composite, and for the 2ZrO2/10TiO2 (mol%) composite the permeability decreases from 1.35 × 10−11 to 4.52 × 10−12 mol cm−1 s−1 Pa−1 as the temperature increases from 30 to 110 °C. A sample (83SiO2–5P2O5–2TiO2/10ZrO2 (mol%)) was selected as an electrolyte for the H2/O2 fuel cell test and yielded the maximum power density value of 10 mW cm−2 using electrochemical measurements at 30 °C under relative humidity atmosphere.