Tomographic Analysis and Modeling of Polymer Electrolyte Fuel Cell Unsupported Catalyst Layers

Abstract

Polymer electrolyte fuel cells' (PEFCs) widespread commercialization is hindered by the devices' limited durability, in terms caused by the corrosion of the carbon support used in the Pt-based PEFC catalysts. Using unsupported electrocatalysts could mitigate such durability issues, but little is known regarding the manner in which their processing into catalyst layers (CLs) affects pore size distribution (PSD) and PEFC performance. Thus, we have used a computational model to investigate the modes of agglomerate packing in CLs made from unsupported Pt 3 Ni nanochain ensembles (aerogels) or Pt black, and complemented this analysis with focused ion beam scanning electron microscopy tomography of corresponding real CLs. 3D structures, PSDs and tortuosities were obtained for real and computed CLs and were found to be in good agreement. The Pt black CL mainly exhibits large and straight pores (>100 nm wide), while the Pt 3 Ni aerogel CL mostly features small and twisted pores (< 100 nm wide) that cause the significantly poorer O 2 mass transport (vs. Pt black) observed in PEFC experiments. Moreover, this modeling approach leads to key insights on the working principle of a filler material used for positively shifting the average PSD and improving the PEFC performance of the Pt 3 Ni CL.

Engineering Catalyst Layers for Next‐Generation Polymer Electrolyte Fuel Cells: A Review of Design, Materials, and Methods

“…[ 487 ] and later work by Ishikawa et al. [ 406 ] reported the use of unsupported Pt 3 Ni aerogel as a CL. The nanochain Pt 3 Ni structure adopted a tortuous gas diffusion pathway that limited performance.…”

“…In this case, Muzaffar et al [ 50 ] has suggested that an instructive way to categorize CLs is into two different proton transport designs: the common GDE, which requires ionomer, and flooded porous electrodes (FPEs), which do not require ionomer. [ 50,198,405 ] CL designs do not require support materials, [ 406 ] and others do not require ionomer as the thickness of the CL is small enough to utilize localized water to transfer protons without significant O 2 diffusion limitations. [ 61,197,200 ] This simplifies the CL structure, eliminating catalyst poisoning by the ionomer and the thickness of the electrode resulting in less tortuous gas transport across the CL and no O 2 diffusion resistance across the ionomer/catalyst boundary (as discussed in Section 3.4).…”

“…[ 292,412,414,415 ] Furthermore, this 3D reconstruction can be used for modeling and simulations of the various transport processes present within the MEA, including O 2 transport, electron conductivity, and proton conductivity, among many others. [ 323,349,406,412,414 ] Other methods have also been utilized to resolve the pore structure, such as X‐ray CT. However, the resolution of X‐ray CT is currently limited, as distinguishing between the NPs of the support/Pt are beyond the resolution of the technique.…”

Microstructure Investigation of Polymer Electrolyte Fuel Cell Catalyst Layers Containing Perfluorosulfonated Ionomer

“…The microstructures of the catalyst inks and CLs have been extensively studied both theoretically [ 8 , 9 ] and experimentally [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ] using techniques such as conventional and cryogenic scanning and transmission electron microscopy (SEM and TEM) [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ], focused ion beam SEM (FIB-SEM) [ 17 , 18 ], atomic force microscopy [ 10 , 19 ], X-ray computed tomography [ 20 ], and X-ray [ 13 , 16 ] and neutron scattering [ 21 ]. Among the scattering techniques, anomalous small-angle X-ray scattering (ASAXS) is a powerful technique that can provide element-specific data from a multicomponent system [ 22 , 23 , 24 , 25 ] and has been used to observe the size distribution of Pt nanoparticles (NPs) in carbon-supported Pt catalysts [ 22 , 23 , 24 ].…”

An Investigation of the Compressive Behavior of Polymer Electrode Membrane Fuel Cell’s Gas Diffusion Layers under Different Temperatures

“…Generally, the cross-section of a GDL is a three-layer structure comprising a substrate, a microporous layer (MPL), and a permeable layer in between. The substrate is a polymer supported by carbon fibers [4,5], carbon felt, carbon cloth [6] or metal foam [7,8] and filled with resins [9,10]. The MPL is usually coated with polytetrafluoroethylene (PTFE).…”