An intermediate-temperature alkaline fuel cell using an Sn0.92Sb0.08P2O7-based hydroxide-ion-conducting electrolyte and electrodes

Abstract

Although various types of anion exchange membrane fuel cells have been developed, few alkaline fuel cells capable of operating at temperatures above 100 °C have been reported, due to low chemical and thermal stability of the polymer electrolytes. Sn_0.92Sb_0.08P₂O₇ is a hydroxide ion conductor that exhibits high conductivities ranging from 10⁻² to 10⁻¹ S cm⁻¹ at elevated temperatures. This report describes the development of an intermediate-temperature alkaline fuel cell using an Sn_0.92Sb_0.08P₂O₇-based electrolyte and electrodes. First, a dense and flexible composite membrane, composed of Sn_0.92Sb_0.08P₂O₇ and polytetrafluoroethylene (PTFE), was synthesized and characterized. In the composite membrane, a homogeneous distribution of Sn_0.92Sb_0.08P₂O₇ particles was obtained at a thickness of 110 μm, yielding hydroxide ion conductivity of ∼10⁻² S cm⁻¹ in the temperature range between 75 and 200 °C. Next, the microstructure of the three-phase boundary in the electrode was established by incorporating Sn_0.92Sb_0.08P₂O₇ particles into the electrode. Consequently, polarization resistance was reduced dramatically compared to that of the unmodified electrode. Finally, fuel cell tests were conducted using the optimized electrolyte and electrode. The peak power density was 76 mW cm⁻² at 75 °C, 94 mW cm⁻² at 100 °C, 114 mW cm⁻² at 125 °C, 130 mW cm⁻² at 150 °C, 132 mW cm⁻² at 175 °C, and 147 mW cm⁻² at 200 °C. High durability of the present fuel cell was also confirmed at 200 °C.