Characterizing automotive fuel cell materials by soft x-ray scanning transmission x-ray microscopy (original) (raw)
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Journal of Physical Chemistry C, 2018
Polymer electrolyte membrane fuel cells (PEMFCs) are a promising and sustainable alternative to internal combustion engines for automotive applications. Polymeric perfluorosulfonic acid (PFSA) plays a key role in PEMFCs as a proton conductor in the anode and cathode catalyst layers, and in the electrolyte membrane. In this study, spectroscopic scanning coherent diffraction imaging (spectro-ptychography) and spectro-ptychographic tomography were used to quantitatively image PFSA ionomer in PEMFC cathodes in both 2D and 3D. We verify that soft X-ray ptychography gives significant spatial resolution improvement on soft matter polymeric materials. A 2D spatial resolution of better than 15 nm was achieved. With better detectors, brighter and more coherent X-ray beams, radiation sensitive PFSA ionomer will be visualized with acceptable levels of chemical and structural modification. This work is a step toward visualization of ionomer in PEM-FC cathodes at high spatial resolution (presently sub-15 nm, but ultimately below 10 nm), which will be transformative with respect to optimization of PEMFC for automotive use.
The Structure of Catalyst Layers and Cell Performance in Proton Exchange Membrane Fuel Cells
JSME International Journal Series B, 2004
A catalyst layer is one of the key elements in polymer electrolyte membrane fuel cells (PEMFC). Improvements in the performance of a membrane electrode assembly (MEA) for PEMFC are much influenced by an electrochemically active surface area in a catalyst layer. But the relation between the structure of a catalyst layer and the cell performance has not been clarified yet. In the present study, catalyst layers with different structure and composition were fabricated, and the structural properties of catalyst layers, such as thickness and roughness, and the polarization curves were measured. The experimental results suggested that there is an optimum mass ratio of electrolyte in a catalyst layer for the cell performance, and the thickness and roughness of a catalyst layer change significantly at the optimum mass ratio.
X-ray Line Profile Analysis of Nanoparticles in Proton Exchange Membrane Fuel Cell Electrodes
The Journal of Physical Chemistry C, 2007
We present a method to extract X-ray diffraction patterns from a multiphase system and analyze the particle size distribution of each phase. The method is demonstrated for crystalline nanoparticles in the electrodes of proton exchange membrane fuel cells (PEMFCs), where it is particularly useful to determine particle size distributions without destroying the device. The structure of the electrodes has a considerable influence on the power and durability of a fuel cell and can be further optimized, for example with respect to the durability of the cell. Since the membrane electrode assembly (MEA) contains multiple and partially X-ray transparent layers, the individual catalyst signals from the anode (platinum-ruthenium alloy) and the cathode (platinum) can be extracted from the diffraction patterns recorded of either side of the MEA using the technique presented in this article. By analysis of the platinum (220) reflection by fitting a pseudo-Voigt function, the individual particle size distributions are determined for the anode and the cathode. The catalyst surface area loss due to particle growth is studied in long-term experiments during the operation of a single model cell for 2100 h and, for comparison, during the storage in different gas atmospheres (Ar, H 2 , and O 2) for 6500 h. With respect to the single cell operation, approximately one-third of the surface is lost in the storage experiment with a slight influence from the gas atmosphere and the catalyst type. The comparison with transmission electron micrographs shows that the size distributions have a similar shape and width but differ in absolute sizes.
Journal of Power Sources, 2017
The cost and performance of proton exchange membrane fuel cells strongly depend on the cathode electrode due to usage of expensive platinum (Pt) group metal catalyst and sluggish reaction kinetics. Development of low Pt content high performance cathodes requires comprehensive understanding of the electrode microstructure. In this study, a new approach is presented to characterize the detailed cathode electrode microstructure from nm to μm length scales by combining information from different experimental techniques. In this context, nanoscale X-ray computed tomography (nano-CT) is performed to extract the secondary pore space of the electrode. Transmission electron microscopy (TEM) is employed to determine primary C particle and Pt particle size distributions. X-ray scattering, with its ability to provide size distributions of orders of magnitude more particles than TEM, is used to confirm the TEMdetermined size distributions. The number of primary pores that cannot be resolved by nano-CT is approximated using mercury intrusion porosimetry. An algorithm is developed to incorporate all these experimental data in one geometric representation. Upon validation of pore size distribution against gas adsorption and mercury intrusion porosimetry data, reconstructed
The Proceedings of the International Conference on Power Engineering (ICOPE), 2003
ABSTIUtCT A catalyst laycr is one of the key elements in PEMFC. A catalyst site must satisfy an electrochemically actiye surface for it to contribute to the clectrochemical reaction in a fuel ccll, To maximizc catalyst utilization, it is desirable to satisfy these three criteria for as many of catalyst sites as possible. The criteria are proton access. gas access, and electronic path continuity. But it is sti11 important to clarify the relation between the structure of a catalyst layer and the cell perfbrmance. in the prescnt study, first catalyst layers with different amounts of components were fabricated. Second, the polarization curves were measured. Finally the thickness and surface of catalyst layers were measured with a micrometer and an atomic force microscope, respectively, and the relation between the structure and composition of a catalyst layer and the cell perfbrmance was discussed.
A PEM fuel cell for in situ XAS studies
Electrochimica Acta, 2005
A miniature proton exchange membrane (PEM) fuel cell has been designed to enable in situ XAS investigations of the anode catalyst using fluorescence detection. The development of the cell is described, in particular the modifications required for elevated temperature operation and humidification of the feed gasses. The impact of the operating conditions is observed as an increase in the catalyst utilisation, which is evident in the EXAFS collected at the Pt L III and Ru K edges for a PtRu/C catalyst. The Pt component of the catalyst was found to be readily reduced by hydrogen in the fuel, while the Ru was only fully reduced under conditions of good gas flow and electrochemical contact. Under such conditions no evidence of O neighbours were found at the Ru edge. The results are interpreted in relation to the lack of surface sensitivity of the EXAFS method and indicate that the equilibrium coverage of O species on the Ru surface sites is too low to be observed using EXAFS.
The effect of materials on proton exchange membrane fuel cell electrode performance
Lancet, 2011
This paper describes the optimisation in the fabrication materials and techniques used in proton exchange membrane fuel cell (PEMFC) electrodes. The effect on the performance of membrane electrode assemblies (MEAs) from the solvents used in producing catalyst inks is reported. Comparison in MEA performances between various gas diffusion layers (GDLs) and the importance of microporous layers (MPLs) in gas diffusion electrodes (GDEs) are also shown. It was found that the best performances were achieved for GDEs using tetrahydrofuran (THF) as the solvent in the catalyst ink formulation and Sigracet 10BC as the GDL. The results also showed that our in-house painted GDEs were comparable to commercial ones (using Johnson Matthey HiSpec TM and E-TEK catalysts).