Construction of Homogeneous Catalyst Layers at Proton Exchange Membrane Fuel Cell Cathodes

Abstract

In proton exchange membrane fuel cells (PEMFCs), the performance of the cathode catalyst layer depends on the effective formation and uniform distribution of the three-phase boundary (catalyst, ionomer, and oxygen). However, traditional cathode catalyst layer structures based on heterogeneous catalysis have reduced the catalyst utilization rate and mass transfer efficiency for the oxygen reduction reaction (ORR), which further restricts the development of PEMFCs. Here, we covalently grafted an ORR molecular catalyst, tetrakis(4-methoxyphenyl) porphyrin iron (II), onto the side chain of a Nafion ionomer. This strategy allows the catalytic center of the transition metal macrocycle to be anchored inside the ion flow channel. Mössbauer spectroscopy showed that the kinetics of the electrode reaction were improved owing to the increase in electron density around the Fe center. Additionally, the improvement in catalytic active site utilization and mass (protons, oxygen) transfer effectively promotes the performance output of the fuel cell. This novel catalyst layer structure may provide a new platform for the development of high-performance molecular catalysts for applications in fuel cells and other energy devices.