Independent regulation of ionomer distribution in catalyst layer for proton exchange membrane fuel cell

The ionomer distribution in the catalyst layer (CL) of proton exchange membrane fuel cell (PEMFC) has become a vital research topic, especially under the low Pt loading condition. In the drying process, the ionomers adsorbed on Pt/C particles in the catalyst ink (called adsorbed ionomers) evolve into a thin ionomer coating on catalyst particles, while free ionomers in the catalyst ink randomly deposit to form ionomer bridges (called deposited ionomers). Many studies have reported the structure and regulation of adsorbed ionomers, but little is known about deposited ionomers which are also important for the formation of CL structure. In this work, a two-pronged CL preparation method is innovatively proposed to achieve independent regulation of the deposited ionomer formed by free ionomers in the catalyst ink, and the effects of different deposited ionomer structures on CL microstructure and fuel cell performance are investigated. Furthermore, the two-pronged method is compared with the conventional method to discuss its feasibility in optimizing the CL structure. The results indicate that the characteristics of free ionomer in the catalyst ink will affect the ionomer distribution and pore structure in the CL by controlling the deposited ionomer, thus determining proton conduction and mass transport. The uniform deposited ionomer morphology and short-side-chain (SSC) ionomer structure make the ionomer distribution in the CL uniform, which promotes proton conduction but also results in high mass transport resistance. Compared with the conventional method, the proton conduction resistance of the electrode prepared by the two-pronged method is decreased by 54.7%, the thickness of ionomer film on catalyst particles surface is decreased by about 2 nm, and the power density of the single cell is increased by 40.4% at the current density of 2500 mA cm−2. These findings provide new insights into the independent regulation of each component in the catalyst ink and the structural optimization of CL.