3D Investigation of Pt-Based Nanocatalyst Durability on High Surface Area Carbon by Automated Electron Tomography
Authors: Amichi Lynda , Yu Haoran , Ziabari Amirkoushyar , Rahman Obaidullah , Arregui-Mena David , Hu Leiming , Neyerlin Kenneth C. , Cullen David A. 
Published: December 2024

Proton-exchange membrane fuel cells (PEMFCs) hold potential for hydrogen-powered heavy-duty vehicles, offering high efficiencies and comparable driving ranges and refueling times to internal combustion engines. Yet, durability challenges persist, notably in cathode catalyst degradation [1]. Understanding degradation mechanisms during accelerated stress tests (AST) is crucial. Electron tomography aids in high-resolution analysis of Pt-based nanoparticle distribution, revealing degradation rates relative to their location on or in the carbon support, and providing a possible explanation to the enhanced particles accessibility at low relative humidity after AST [2,3].

In this work, we developed an automated electron tomography workflow performed in the scanning transmission electron microscopy (STEM) utilizing SerialEM for data acquisition[4]. Data were reconstructed using a model-based iterative reconstruction with adaptive regularization (MBIR-ARAR) [5], and the segmentation of the nanoparticles and carbon was performed using the commercial software Avizo.

We examined Pt catalyst particle size distributions at both the beginning (BOT) and end (EOT) of the test (see Figure 1). Our results revealed a noticeable increase in particle size alongside a reduction in specific surface area (SSA), regardless of nanoparticle location. Moreover, a significant portion of particles remained within the carbon pores at EOT. In addition, there was evidence of an expanded size distribution of pores post AST, potentially due to minor carbon corrosion. These observed degradation mechanisms challenge the assumption that Pt dissolution from the interior of the carbon support and re-deposition on the surface is a predominant factor for the enhanced accessibility after AST [6] but suggests that other factors such as carbon corrosion causing pore opening and increased ionomer intrusion. Additionally, we will discuss the potential of employing low-dose cryo-tomography to mitigate damage to the catalyst, support, and particularly beam sensitive proton conducting ionomer [7,8].

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This material is based on work performed by the Million Mile Fuel Cell Truck (M2FCT) Consortium, 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. Electron microscopy research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.

Figure 1