Effect of Alloying on Microstructure and Transport Properties in the Catalyst Layer of Proton Exchange Membrane Fuel Cells

Low platinum (Pt) is important to reduce the cost of fuel cells and promote their large-scale application. Alloying strategy is the key solution to reduce Pt. However, the surface microstructure on Pt-alloy nanoparticles is significantly different from that of Pt, affecting the efficiency of the electrochemical reaction. Thus, it is essential to study the microstructure of the surface on Pt-alloy catalysts to promote their application. In this work, the analysis of catalyst layers prepared with Pt–Co/C or Pt/C was conducted. Molecular dynamics simulations revealed that the binding force of the ionomer on the surface of Pt–Co was stronger than that on Pt. It caused more ionomer to adsorb onto the surface of Pt–Co, which was proved by TEM images. It resulted in higher local oxygen mass transfer resistance. The transport coefficient, solubility, and permeability coefficient of oxygen molecules in Pt–Co were all lower than those in Pt, leading to higher concentration polarization. Also, the Pt–Co particles tend to aggregate more easily to form a larger size, which is unfavorable for the construction of a uniform catalyst layer structure. MEA–Pt-Co/C exhibited higher maximum performance than MEA-Pt/C under low relative humidity conditions. However, the concentration polarization of MEA–Pt-Co/C increases rapidly at high current densities, leading to a rapid decline in the performance. Thus, it is necessary to design matched catalyst layer structures for Pt-alloy catalysts, which is essential for the development of platinum reduction technology in fuel cells.