Enhancement of proton exchange membrane fuel cells performance at elevated temperatures and lower humidities by incorporating immobilized phosphotungstic acid in electrodes

• Adding PWA/SiO2 both in the membrane and electrodes increases the MEA performance.
• The proton conductivities in the electrodes increase.
• The proton transport across the membrane/electrode interfaces increases.
• Immobilized PWA/SiO2 in the electrodes does not poison the electrocatalysts.

Doping phosphotungstic acid immobilized by silicon dioxide (PWA/SiO2) in a Nafion membrane is an effective way to achieve a good proton conductivity of the membrane in proton exchange membrane fuel cells (PEMFCs) at elevated temperatures and lower humidity. To further advance the theory, immobilized PWA/SiO2 was incorporated in the Nafion ionomer as the binder and proton conductor in the electrode matrices for additional performance enhancement. Two sets of membrane electrode assemblies (MEAs) were prepared and tested by incorporating PWA/SiO2 both in the membrane and electrodes (MEA-1) and only in the membrane (MEA-2). Analyses of the ohmic resistance, open circuit voltage, Tafel slope, charge transfer time constant of the two MEAs indicate that the superior performance of MEA-1 at elevated temperatures and low relative humidities was primarily ascribed to a better hydration of electrodes. The protonic transports across the interfaces between the electrodes and membrane were also improved, which has less impact on the performance enhancement. These results also show that the immobilized PWA/SiO2 in the electrodes did not exhibit poisoning effects on the electrocatalysts. The lack of poisoning effects is attributed to the stabilization of PWA in ionic channels with Nafion ionomer which does not interact with the electrocatalysts.