Effect of platinum loading on fuel cell cathode performance using hydrocarbon ionomers as binders

Area of Science:

• Electrochemistry
• Materials Science
• Energy Conversion

Background:

• Fuel cells are crucial for clean energy, but high platinum costs necessitate reduced loading.
• Ion-conducting polymers (ionomers) are vital as electrode binders in fuel cell cathodes.
• Understanding how binder properties affect performance at low platinum loadings is key.

Purpose of the Study:

• To investigate the impact of reduced platinum loading on cathode performance in hydrogen/oxygen fuel cells.
• To compare the effectiveness of different ionomers (Nafion, SPI-8, SPEEK) as electrode binders under varying humidity conditions.
• To elucidate the role of binder-catalyst interactions in determining performance at low platinum loadings and low humidity.

Main Methods:

• Fabrication of Membrane Electrode Assemblies (MEAs) with varying platinum loadings.
• Electrochemical characterization of cathode performance, including polarization measurements.
• Analysis of mass transport and activation overpotential under different relative humidity (RH) conditions.

Main Results:

• Lowering platinum loading decreased cathode polarization at high humidity (90-100% RH) for both SPI-8 and SPEEK binders, attributed to improved mass transport.
• At low humidity (<80% RH), reduced platinum loading increased cathode polarization for SPI-8 due to higher activation overpotential.
• The effect of platinum loading was less pronounced with SPEEK, suggesting different binder-catalyst interactions at low humidity.

Conclusions:

• Binder choice significantly influences fuel cell cathode performance at low platinum loadings and low humidity.
• SPEEK demonstrates a smaller performance decrease than SPI-8 when platinum loading is reduced at low humidity.
• Specific adsorbability of hydrocarbon binders on platinum catalysts is a critical factor for optimizing performance under challenging conditions.