Fabrication and characterization of solid state proton conductor (NH4)2SiP4O13–NH4PO3 for fuel cells operated at 150–250 °C

NH4PO3–(NH4)2SiP4O13 composite, a potential electrolyte for intermediate temperature fuel cells that operated around 250 °C, was synthesized with a solid-state reaction method. Electromotive forces (emfs) as measured with hydrogen concentration cells showed that the composite was a pure proton conductor at hydrogen partial pressure from 102 to 105 Pa. Its proton transference numbers were determined to be 1.0 at 150 °C, 0.99 at 200 °C, and 0.99 at 250 °C. Fuel cells that used NH4PO3–(NH4)2SiP4O13 as electrolytes were also fabricated. Maximum power density was 6.6 mW/cm2 at 250 °C when dry hydrogen and dry oxygen were used as the fuel and oxidant, respectively. Improved cell performance is expected by increasing cathode activity, increasing the electrolyte density, and decreasing the electrolyte thickness.