Ionomer distribution control by self-assembled monolayers for high-power and low Pt-loaded proton exchange membrane fuel cells

Reducing Pt loading in the cathode catalyst layers (CCLs) is extremely desirable to keep costs down for proton exchange membrane fuel cells (PEMFCs). However, as the Pt loading decreases, low Pt-loaded membraneelectrode assemblies (MEAs) encounter high voltage losses at high current densities. These voltage losses are attributed to the mass transfer resistance of oxygen through the ionomer-Pt interface. Herein, we present a selective ionomer distribution design that significantly decreases local oxygen transport resistance. Hydrophobic self-assembled monolayers (SAMs) modify PtM (M = Mn and Co) surface to enable control deposition of ionomer film on the vicinity of PtM particles. The SAMs are then removed from CCLs through a voltage cycling activation process, regain the oxygen reduction reaction (ORR) ability of the PtM. The electrochemical evaluation presents a decreased O2 transfer resistance (OTR) and a following increase in the power property. Due to the polar interaction between the sulfonate groups of the ionomer side chain and SAMs on the PtM surface, highly selective ionomer distribution is assured during the MEA production process.

Automated summary

A new method is proposed in this study to reduce the transport resistance at the ionomer-Pt interface by selective ionomer distribution design, leading to improved performance of the membrane-electrode assemblies.