Unraveling the core of fuel cell performance: engineering the ionomer/catalyst interface

Chenzhao Li, Kang Yu, Ashley Bird, Fei Guo, Jan Ilavsky, Yadong Liu, David A. Cullen, Ahmet Kusoglu, Adam Z. Weber, Paulo J. Ferreira, Jian Xie

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

The biggest obstacle to the widespread implementation of polymer electrolyte membrane fuel cells (PEMFCs) is their cost, primarily due to the use of platinum catalysts. The high intrinsic catalyst activity exhibited on a rotating disk electrode (RDE) is rarely realized in a membrane electrode assembly (MEA), which is a long-standing challenge for PEMFCs and a cause of low catalyst utilization. To translate the high RDE performance of a catalyst into a MEA, the design of an ideal ionomer/catalyst interface is proposed: a thin, conformal ionomer film covers the maximum surface of a Pt nanoparticle and thus simultaneously maximizes catalyst utilization, (i.e., high mass activity and electrochemically active surface area) and O2 diffusion rate (i.e., high current density performance) without compromising proton conduction. Building such an interface is a long-standing challenge due to the lack of interaction between the ionomer and catalyst particles, resulting in large ionomer agglomerates and inhomogeneous ionomer coverage over the catalyst nanoparticle, with consequent poor fuel cell performance. In this work, this ionomer/catalyst interface has been engineered, utilizing the electrostatic attraction between positively charged catalyst and negatively charged ionomer particles in a catalyst ink and preserved in a solid catalyst layer. As a result, this interface leads to previously unachieved proton exchange membrane fuel cell performance in terms of both catalyst utilization (75% vs. 45%) and peak/rated power density (i.e., 1.430/0.930 W cm−2, H2/air, cathode Pt loading: 0.1 mgPt cm−2) for pure Pt catalysts, even better than those of Pt alloy catalysts. This work demonstrates the formation of an interface in the liquid phase (using ultra-small-angle X-ray scattering in combination with cryo-TEM, isothermal-titration-calorimetry) and the preservation of the interface in the solid catalyst layer (using TEM) and estimates the effective coverage and thickness of the ionomer film (using limiting current density, RDE and fuel cell performance).

Original languageEnglish
Pages (from-to)2977-2990
Number of pages14
JournalEnergy and Environmental Science
Volume16
Issue number7
DOIs
StatePublished - May 11 2023

Funding

The authors would like to thank Dr Fan Yang and Dr Le Xin for their help at beginning of this work, Mr Guangqi Zhu and Ms Qi Zhang for their help at the revision period of this work, and Dr Sarah A. Berlinger and Dr Behzad Rad for helpful discussions. This work is supported by the Million Mile Fuel Cell Truck (M2FCT) Consortium ( https://millionmilefuelcelltruck.org ), technology manager Greg Kleen, which is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, under contract number DE-AC02-05CH1123. ITC work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract no. DE-AC02-05CH11231. A. B. acknowledges support from the Graduate Research Fellowship Program by the National Science Foundation under Grant No. DGE 1752814. This research used resources of the Advanced Photon Source; a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract no. DE-AC02-06CH11357. High-resolution cryo-TEM was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. The authors acknowledge the support by FCT, through IDMEC, under LAETA, project UIDB/50022/2020.

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