skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Impact of Platinum Loading and Layer Thickness on Cathode Catalyst Degradation in PEM Fuel Cells
In this work we investigate the effect of platinum loading and layer thickness on cathode catalyst degradation by a comprehensive in situ and STEM-EDS characterization. To decouple the effect of the platinum loading and layer thickness from each other, the experiments were categorized in two sets, each with cathode loadings varying between 0.1 and 0.4 mgPtcm−2: (i) Samples with a constant Pt/C ratio and thus varying layer thickness, and (ii) samples with varying Pt/C ratios, achieved by dilution with bare carbon, to maintain a constant layer thickness at different platinum loadings. Every MEA was subjected to an accelerated stress test, where the cell was operated for 45,000 cycles between 0.6 and 0.95 V. Regardless of the Pt/C ratio, a higher relative loss in electrochemically active surface area was measured for lower Pt loadings. STEM-EDS measurements showed that Pt was mainly lost close to the cathode—membrane interface by the concentration driven Pt2+ion flux into the membrane. The size of this Pt-depletion zone has shown to be independent on the overall Pt loading and layer thickness, hence causing higher relative Pt loss in low thickness electrodes, as the depletion zone accounts for a larger fraction of the catalyst layer.  more » « less
Award ID(s):
1919280
PAR ID:
10477258
Author(s) / Creator(s):
; ; ; ; ; ;
Publisher / Repository:
The Electrochemical Society
Date Published:
Journal Name:
Journal of The Electrochemical Society
Volume:
170
Issue:
2
ISSN:
0013-4651
Page Range / eLocation ID:
024506
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; (, Journal of The Electrochemical Society)
    Proton Exchange Membrane (PEM) fuel cells are a suitable electrochemical power source for heavy duty vehicle (HDV) applications due to their high efficiency and durability. The cathode of the fuel cell uses a higher geometric loading of platinum (∼0.2 to 0.4 mgPt/cm2) for the electrocatalysis of the kinetically sluggish Oxygen Reduction Reaction (ORR) which requires higher weight percent loading of the metal (∼50%) on the carbon support to decrease the catalyst layer thickness and hence, the reactant transport losses. The conventionally used supports for platinum catalyst, such as the KetjenBlackTMtype high surface area carbon (HSC) features limited mesopore area for the dispersion of Pt nanoparticles leading to increased aggregation and poor durability. Here, we show a new class of carbon materials known as the Engineered Catalyst Support (ECS) developed by Pajarito Powder with higher mesopore fraction for the dispersion of higher weight percentage of Pt nanoparticles. ECS materials can disperse up to 50% Pt by weight of the catalyst thereby enabling lower catalyst layer thickness with higher performance retained after durability test. A comprehensive set of physico-chemical and electrochemical studies in membrane electrode assembly (MEA) are reported to understand the performance and durability of Pt/ECS catalysts. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, Advanced Energy Materials)
    Abstract Iron‐nitrogen‐carbon (Fe‐N‐C) single‐atom catalysts are promising sustainable alternatives to the costly and scarce platinum (Pt) to catalyze the oxygen reduction reactions (ORR) at the cathode of proton exchange membrane fuel cells (PEMFCs). However, Fe‐N‐C cathodes for PEMFC are made thicker than Pt/C ones, in order to compensate for the lower intrinsic ORR activity and site density of Fe‐N‐C materials. The thick electrodes are bound with mass transport issues that limit their performance at high current densities, especially in H2/air PEMFCs. Practical Fe‐N‐C electrodes must combine high intrinsic ORR activity, high site density, and fast mass transport. Herein, it has achieved an improved combination of these properties with a Fe‐N‐C catalyst prepared via a two‐step synthesis approach, constructing first a porous zinc‐nitrogen‐carbon (Zn‐N‐C) substrate, followed by transmetallating Zn by Fe via chemical vapor deposition. A cathode comprising this Fe‐N‐C catalyst has exhibited a maximum power density of 0.53 W cm−2in H2/air PEMFC at 80 °C. The improved power density is associated with the hierarchical porosity of the Zn‐N‐C substrate of this work, which is achieved by epitaxial growth of ZIF‐8 onto g‐C3N4, leading to a micro‐mesoporous substrate. 
    more » « less
  3. ; ; ; ; (, Angewandte Chemie International Edition)
    Abstract Oxide supports with well‐defined shapes enable investigations on the effects of surface structure on metal–support interactions and correlations to catalytic activity and selectivity. Here, a modified atomic layer deposition technique was developed to achieve ultra‐low loadings (8–16 ppm) of Pt on shaped ceria nanocrystals. Using octahedra and cubes, which expose exclusively (111) and (100) surfaces, respectively, the effect of CeO2surface facet on Pt‐CeO2interactions under reducing conditions was revealed. Strong electronic interactions result in electron‐deficient Pt species on CeO2(111) after reduction, which increased the stability of the atomically dispersed Pt. This afforded significantly higher NMR signal enhancement in parahydrogen‐induced polarization experiments compared with the electron‐rich platinum on CeO2(100), and a factor of two higher pairwise selectivity (6.1 %) in the hydrogenation of propene than any previously reported monometallic heterogeneous Pt catalyst. 
    more » « less
  4. ; ; (, Journal of Applied Electrochemistry)
    During high current density operation, water production in the polymer electrolyte membrane fuel cell (PEMFC) cathode catalyst layer can negatively affect performance by lowering mass transport of oxygen into the cathode. In this paper, a novel heat treatment process for controlling the ionic polymer/gas interface property of the fuel cell catalyst layer is investigated and then incorporated into the membrane electrode assembly (MEA) fabrication process. XPS characterization of the catalyst layer’s ionomer-gas interface at its outer surface and its sublayers’ surfaces obtained by scraping off successive layers of the catalyst layers confirms that a hydrophobic ionomer interface can be achieved across the catalyst layer using a specific heat treatment condition. Based on the results of the catalyst layer study, the MEA fabrication process is modified to identify heat treatment configuration and conditions that will create an optimal hydrophobic ionomer-gas interface inside the cathode catalyst layer. Finally, fuel cell tests conducted on the conventional and new MEAs under different operating temperatures show the performance of the fuel cells with the treated MEAs was > 130% higher than that with the conventional MEA at 25 °C and 70 °C with humidified air and > 45% higher at 70 °C with dry air. The durability of the hydrophobic treatment on the cathode catalyst layer ionomer is also confirmed by the accelerated stress test. 
    more » « less
  5. ; ; ; ; ; (, Nature Communications)
    Abstract Ionic liquids (ILs) have shown to be promising additives to the catalyst layer to enhance oxygen reduction reaction in polymer electrolyte fuel cells. However, fundamental understanding of their role in complex catalyst layers in practically relevant membrane electrode assembly environment is needed for rational design of highly durable and active platinum-based catalysts. Here we explore three imidazolium-derived ionic liquids, selected for their high proton conductivity and oxygen solubility, and incorporate them into high surface area carbon black support. Further, we establish a correlation between the physical properties and electrochemical performance of the ionic liquid-modified catalysts by providing direct evidence of ionic liquids role in altering hydrophilic/hydrophobic interactions within the catalyst layer interface. The resulting catalyst with optimized interface design achieved a high mass activity of 347 A g−1Ptat 0.9 V under H2/O2, power density of 0.909 W cm−2under H2/air and 1.5 bar, and had only 0.11 V potential decrease at 0.8 A cm−2after 30 k accelerated stress test cycles. This performance stems from substantial enhancement in Pt utilization, which is buried inside the mesopores and is now accessible due to ILs addition. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email