Electrolyte Membrane Fuel Cell Catalyst Research Articles

Stable platinum nanostructures on nitrogen-doped carbon obtained by high-temperature synthesis for use in PEMFC

We propose a novel, facile synthesis route to produce stable platinum-based polymer electrolyte membrane fuel cell catalysts supported on nitrogen-doped carbon. Platinum nanoparticles were decorated on polyaniline (PANI), a nitrogen-containing polymer, before its subsequent carbonization at 750 °C under nitrogen atmosphere. Thus, nitrogen-doped carbon-supported platinum catalysts were produced with homogeneously distributed small metal particles, which are otherwise difficult to obtain. Most remarkably the platinum nanoparticles did not grow significantly during the carbonization step. In contrast, commercially available standard catalysts on carbon materials subjected to the same heat treatment showed severe particle growth. In accordance with the high thermal stability, the PANI-derived catalyst shows good long-term stability in accelerated stress test and a promising performance as cathode material in 5 × 5 cm2 single cells. The synthesis is carried out without the need for special laboratory equipment, so it will be easy to scale up for industrial catalyst production.

U.S. Department of Energy Polymer Electrolyte Membrane Fuel Cell Catalyst Development Activities

The U.S. Department of Energy's (DOE's) Fuel Cell Technologies Program supports research and development of electrocatalysts for polymer electrolyte membrane fuel cells. R&D projects address cost, durability, and performance with the goal of reducing or eliminating platinum group metals from the catalysts. The projects' strategies include: ultra-low platinum loading, platinum alloy catalysts, novel architectures, and non-PGM catalysts. The deposition of Pt monolayers on Pd nanoparticles was improved by displacement of Pd by Pt; the catalyst activity is comparable to those fabricated using Cu underpotential deposition. The specific activity of nanoparticles can be improved by ~4x using ternary alloys. Catalysts, prepared with excess non-noble elements that are removed during processing, i.e., dealloying, attain a mass activity exceeding that of commercial catalysts. Extended catalyst surfaces on nanotubes, nanowires, and metal oxides have been developed. Results from DOE's catalyst projects will be discussed in detail.

Transition Metal Ion-Chelating Ordered Mesoporous Carbons as Noble Metal-Free Fuel Cell Catalysts

A new concept for noble metal-free polymer electrolyte membrane fuel cell catalysts has been developed. The catalysts consist of chelated transition metal ions incorporated in a nitrogen-functionalized ordered mesoporous carbon matrix, which is evidenced by a combination of X-ray absorption fine structure analysis and high-resolution transmission electron microscopy. The ordered mesoporous carbon matrix of the catalyst offers an exceptionally high specific surface area and allows conceptually for a high degree of tuning, enabling controlled variability of, e.g., pore size and curvature and thickness of the pore walls of the catalysts. Single cell fuel cell tests of membrane electrode assemblies prepared with a cathode made of iron- or cobalt-based versions of the catalyst show high power densities, reaching up to one-third of a commercial Pt/C catalyst at 0.6 V.

U.S. Department of Energy Polymer Electrolyte Membrane Fuel Cell Catalyst Development Activities

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Effect of mechanical vibration on platinum particle agglomeration and growth in Polymer Electrolyte Membrane Fuel Cell catalyst layers

The effect of mechanical vibration on Platinum (Pt) particle agglomeration and growth in the catalyst layer of a Membrane Electrode Assembly (MEA) for a Proton Exchange Membrane Fuel Cell (PEMFC) was investigated. A series of experiments were conducted using a 300-h accelerated test with potential cycling and transmission electron microscopy (TEM). Each of the 300-h accelerated tests used different constant mechanical vibration conditions (frequency and acceleration). It was observed that the average diameter of Pt particles under vibration is 10% smaller than the ones that were under no vibration conditions. The Pt particles in the order of 2–2.5 nm in the pristine state have grown to approximately 6 nm (after 300-h accelerated test without vibration condition) and to approximately 5.47 nm (after 300 h accelerated test under 1 g 20 Hz vibration condition).

Magneli phase Ti n O2n − 1 as corrosion-resistant PEM fuel cell catalyst support

Magneli phase titanium suboxide, Ti n O2n − 1, with Brunauer–Emmett–Teller surface area up to 25 m2 g−1 was prepared using the heat treatment of titanium oxide (rutile) mixed with polyvinyl alcohol in ratios from 1:3 to 3:1. XRD patterns showed Ti4O7 as the major phase formed during the heat treatment process. The Ti n O2n − 1 showed excellent electrochemical stability in the potential range of −0.25 to 2.75 V vs. standard hydrogen electrode. The Ti n O2n − 1 was employed as a polymer electrolyte membrane fuel cell catalyst support to prepare 20 wt% platinum (Pt)/Ti n O2n − 1 catalyst. A fuel cell membrane electrode assembly was fabricated using the 20 wt% Pt/Ti n O2n − 1 catalyst, and its performance was evaluated using H2/O2 at 80 °C. A current density of 0.125 A cm−2 at 0.6 V was obtained at 80 °C.

U.S. Department of Energy Polymer Electrolyte Membrane Fuel Cell Catalyst Development Activities

The U.S. Department of Energy is supporting the research, development, and deployment of all types of fuel cells for transportation, material handling, portable power, back-up power, stationary power, and combined heat and power applications. A major focus of this support is polymer electrolyte membrane fuel cells. Key issues inhibiting their widespread penetration and commercialization of fuel cells are performance, durability, and cost and a key component is electrode technology including supports and catalysts. The approaches to improvement in electrode technology include alloys, core/shell structures, thin continuous catalyst films, non-precious metal catalysts, and alternative supports. Major progress has been realized recently. This paper provides an overview of DOE-funded advances and status.

U.S. Department of Energy Polymer Electrolyte Membrane Fuel Cell Catalyst Development Activities

not Available.

Nafion Film-Templated Platinum Electrodes for Oxygen Reduction

Nanostructured platinum electrodes were prepared by electrodeposition of platinum onto Nafion-coated gold rotating-disk electrodes (RDEs). The resultant material was characterized in acidic electrolyte by voltammetry and has been examined for electrocatalytic activity toward the oxygen reduction reaction (ORR). The platinum templated with a 3-μm Nafion film exhibited improved oxygen reduction performance in comparison to platinum-modified gold RDE prepared without templating. The mass and specific activities increased by a factor of two for the Nafion film-templated electrode, and the ORR half-wave potential (at 0.5iL) was shown to shift by 60 mV. Considering that the specific surface areas of the 3-μm Nafion film-templated and untemplated Pt were similar (14.1 vs. 11.8 m2 g−1), the enhanced kinetic performance of the former points to subtle catalyst morphology effects. The proposed method could be advantageous for the preparation of polymer electrolyte membrane fuel cell catalyst layers where the Nafion film serves also as the ionic conductor network.

On the Micro-, Meso-, and Macroporous Structures of Polymer Electrolyte Membrane Fuel Cell Catalyst Layers

In this work, N(2) adsorption was employed to investigate the effects of carbon support, platinum, and ionomer loading on the microstructure of polymer electrolyte membrane fuel cell catalyst layers (CLs). Brunauer-Emmett-Teller and t-plot analyses of adsorption isotherms and pore-size distributions were used to study the microstructure of carbon supports, platinum/carbon catalyst powders, and three-component platinum/carbon/ionomer CLs. Two types of carbon supports were chosen for the investigation: Ketjen Black and Vulcan XC-72. CLs with a range of Nafion ionomer loadings were studied in order to evaluate the effect of an ionomer on the CL microstructure. Regions of adsorption were differentiated into micropores associated with the carbon primary particles (<2 nm), mesopores ascribed to the void space inside agglomerates (2-20 nm), and meso- to macroporous space inside aggregates of agglomerates (>50 nm). Ketjen Black was found to possess a significant fraction of micropores, 25% of the total pore volume, in contrast to Vulcan XC-72, for which the corresponding fraction of micropores was 15% of the total pore volume. The microstructure of the carbon support was found to be a significant factor in the formation of the microstructure in the three-component CLs, serving as a rigid porous framework for distribution of platinum and the ionomer. It was found that platinum particle deposition on Ketjen Black occurs in, or at the mouth of, the support's micropores, thus affecting its effective microporosity, whereas platinum deposition on Vulcan XC-72 did not significantly affect the support's microstructure. The codeposition of ionomer in the CL strongly influenced its porosity, covering pores < 20 nm, which are ascribed to the pores within the primary carbon particles (pore sizes < 2 nm) and to the pores within agglomerates of the particles (pore sizes of 2-20 nm).

A review on polymer electrolyte membrane fuel cell catalyst degradation and starvation issues: Causes, consequences and diagnostic for mitigation

In proton exchange membrane fuel cells, cost, reliability and durability are important issues that need to be solved before their commercialization. Their performance decrease during operation is attributed, amongst others, to the loss of electrochemical surface area occurring during long-term ageing, after transients or after an incident (faulty operation). These losses are mainly due to catalyst metal degradation and carbon-support corrosion, which are continuous irreversible processes that can dramatically reduce the fuel cell lifetime. In this paper, the phenomena linked to catalyst and carbon-support degradation are reviewed, focusing on those caused by fuel and oxidant starvation, since these faulty conditions are amongst the most critical for fuel cell durability. A description of reactions potentially involved in the catalyst degradation, associated with thermodynamic and kinetic considerations related to fuel cell operation are reviewed. This information is used to interpret the experimental results presented in the literature and reviewed in this paper. Based on these reviews, an analysis of the “reverse decay current mechanism” is performed and an alternative mechanism is suggested together with an experiment that would identify the most likely between them. Finally, some characterization methods or mitigation strategies are listed and an illustrative fault tree is built, pointing out the relationship between causes and symptoms in catalyst degradation.

Dissolution Behavior of Pt Alloy Catalysts in Sulfuric Acid Solution

The dissolution behavior of platinum alloy has been investigated for application in polymer electrolyte membrane fuel cell catalyst. Pt alloys (Pt-Co, Pt-Ni, Pt-Fe) were prepared by arc melting. The electrochemical behavior was studied by cyclic voltammetry (CV) in 0.5M H2SO4 at 298 K. The test solutions were analyzed by using ICP to determine the amount of dissolved ions. The results of CV of Pt-Co, Pt-Ni and Pt-Fe alloy electrodes indicated that the current density of Pt-Co, Pt-Ni was much smaller than that of Pt-Fe alloy and close to that of Pt electrode. The ICP results revealed that amount of dissolution for Pt-Co and Pt-Ni alloys were much lower than that for Pt-Fe alloy.

Quasi-elastic Neutron Scattering Investigation of the Hydrogen Surface Self-Diffusion on Polymer Electrolyte Membrane Fuel Cell Catalyst Support

Quasi-elastic neutron scattering (QENS) measurements have been performed to investigate the surface self-diffusion of hydrogen molecules. A monolayer of molecular hydrogen was adsorbed on a carbon material commonly used in polymer electrolyte membrane fuel cells, called XC-72. QENS spectra were recorded at the time-of-flight spectrometer IN5 at Institut Laue-Langevin (ILL) in Grenoble at 40, 50, 60, and 70 K. By using the Chudley & Elliott model for jump diffusion, we found the diffusion coefficient at each temperature. The logarithm of the diffusion coefficient was plotted versus the inverse of the temperature to give the coefficient in the Arrhenius equation. From this, we can estimate the diffusion at higher temperatures as well. Our observed diffusion follows the same trend as that found for hydrogen molecules on the surface of single-walled carbon nanotubes and Grafoil.