Improving PEMFC Performance with Customized Catalyst Combinations and Advanced Mixing Techniques
Authors: Lee Jieun , Cho Sung Yong , Cho Youngick , Cho Minju , Lee Sungchul 
Published: February 2024

Proton Exchange Membrane Fuel Cells (PEMFCs) are a popular choice for use in vehicles and buildings because they can operate at relatively low temperatures and have a simpler system compared to other types of fuel cells. The performance and durability of PEMFCs are influenced by the membrane electrode assembly (MEA).

The cathode, where the oxygen reduction reaction occurs, is the component of the MEA that has the greatest influence on performance. The factors that affect high power performance are catalyst activity, proton conductivity, and mass transport resistance of fuels and products.

Pt catalysts and PtCo catalysts have advantages and disadvantages at different current densities in PEMFCs. In low current density conditions, PtCo catalysts have been shown to exhibit higher catalytic activity compared to Pt catalysts for the oxygen reduction reaction (ORR). This can result in a more efficient fuel cell operation. However, in high current density conditions, the activity of PtCo catalysts can be reduced compared to Pt catalysts because of their larger particle sizes, which can limit their performance.

The properties of the carbon support, such as its hydrophobicity and surface area, can also play an important role in determining the performance of the fuel cell. Hydrophobic carbon supports can facilitate gas diffusion and prevent flooding which can occur when water accumulates in the pores of the electrode and limits reactant transport. Moreover, such supports can limit the contact area between the water and catalyst, leading to prolonged catalyst activity and lifespan. On the other hand, high surface area supports can increase the number of sites available for catalyst anchoring and enlarge the electrode's effective surface area. However, achieving both hydrophobicity and high surface area can be challenging due to the trade-off between these properties.

Because each catalyst has advantages and disadvantages at different current densities or operating conditions in PEMFCs, combining different catalystscan achieve improved performance across a wider range of operating conditions. However, each catalyst and carbon support has different affinity with ionomer. Therefore, it is impossible to achieve even ionomer distribution through simple mixing. This means that it is difficult to express the advantages of each catalyst through simple mixing because the transport properties of protons can be influenced by the distribution of the ionomer.

To address this, two catalysts were mixed into thecathode electrodes separately, and it was confirmed that this approach improved their performance across a range of current densities. In particular, their high power characteristics were enhanced. To confirm these results, the MEA was tested using H2/air polarization curves, EIS analysis, and limit current density tests, and the porosity in the electrode structure was measured by the BET method and Mercury intrusion porosimetry (MIP).

In conclusion, Pt and PtCo catalysts have unique advantages and disadvantages at different current densities in PEMFCs. The properties of the carbon support also play a crucial role in determining the fuel cell performance. Combining different catalysts can enhance the fuel cell's performance but achieving even ionomer distribution through simple mixing is challenging. Applying the two catalysts separately through a distribution process improved the fuel cell's performance across different current densities, especially high power characteristics.