Influence of pore size optimization in catalyst layer on the mechanism of oxygen transport resistance in PEMFCs

• Published in: Progress in natural science 2020-12, Vol.30 (6), p.839-845
• Main Authors: Guan, Shumeng, Zhou, Fen, Tan, Jinting, Pan, Mu
• Format: Article
• Language: English
• Subjects: Oxygen transport resistance; PEMFC; Pore size optimization; Pore-forming agent
• ISSN: 1002-0071
• DOI: 10.1016/j.pnsc.2020.08.017

In PEMFC, the oxygen transport resistance severely hinders the cell from achieving high performance. In this paper, pore-forming agent was used to optimize the pore size distribution of the catalyst layer (CL), and to study its effect on the mechanism of oxygen transport resistance, including molecular diffusion resistance, Knudsen diffusion resistance, and local O2 resistance in CL. The results showed that with the pore formation the cell performance had a significant improvement at high current density, mainly due to its better oxygen transport properties, especially under low platinum conditions. The addition of pore-forming agent moved the pore diameter toward a larger pore diameter with a range from 70 to 100 nm, and also obtaining a higher cumulative pore volume. It was found that the increase of the cumulative pore volume and larger pore size were conducive to the diffusion of oxygen molecules in CL, and the resistance caused by which was the dominant part in total transport resistance. Further tests indicated that the improvement of molecular diffusion resistance was much larger than that of Knudsen diffusion resistance in the catalyst layer after pore formed. In addition, the optimized pore structure will also get a higher number of effective pores, which resulted in an increased effective area of the ionomer on the Pt surface. The higher effective area of the ionomer was particularly beneficial for the reduction of local O2 resistance with low Pt loading. •The pore size of the CL was successfully optimized by adding pore-forming agent.•The modified CL better delays the arrival of mass-transport polarization.•The oxygen transport resistance decreases after pore-formed, which is more obvious under low Pt loading.•Increasing a number of large pore with diameter of 70–100 nm results in a decrease of RCL,Fick.•Adding pore-forming agent can increase the effective oxygen transport ionomer area, which is beneficial to reduce RLocal.