Proton-Conducting SnP2O7 Electrolyte for Intermediate Temperature PEMFC Under Low Humidificatio

Abstract

Current fuel cells for transportation and residential applications use polymer electrolyte membrane fuel cells (PEMFCs) which require platinum catalysts and operate below 80 °C due to water management issues. However, PEMFCs operating at 100 °C or higher temperatures in anhydrous conditions do not need a humidifier, and do not suffer from water management issues created by the presence of liquid water. Excessive amount of liquid water in the electrode can flood the backing and catalysts layers at lower temperatures leading to poorer fuel cell performance. Furthermore, such intermediate temperature PEMFCs can solve the problem of carbon monoxide (CO) poisoning of the anode electrocatalyst leading to relaxation of the hydrogen fuel quality standards, thus lowering infrastructure costs. Finally, higher operating temperatures allow for simpler cooling systems in transportation applications, which results in smaller and lighter radiators. These advantages mean that a paradigm shift in fuel cells for transportation and residential applications can be achieved with an intermediate temperature proton conducting solid-electrolyte that can operate above 150 °C. Unfortunately, electrolyte membranes and ionomers developed so far do not have satisfactory conductivity and performance in the above temperature ranges, at low-humidity, or in non-humidified conditions. The further advancement of higher temperature PEMFCs relies on the development of membranes that possess the desired electrochemical and mechanical properties in dry (< 30% RH) and hot (> 100 oC) conditions. In this study, we have developed an organic/inorganic composite membrane using a SnP2O7 (TPP) inorganic conductor and evaluated the fuel cell performance under various conditions. Membrane electrode assemblies (MEA) were prepared from these membranes and gas diffusion electrodes (GDE) were optimized using either LANL ionomer dispersion or various commercial gas diffusion layer (GDL). A maximum power density (> 600mW/cm2 ) has been obtained for fuel cell operation at ≈ 220 oC under less than 2 % humidification condition.