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Microstructural Characterization of Proton Exchange Membrane (PEM) Fuel Cells
Pt-Co catalysts exhibit a lower loss of surface area compared with Pt during potential cycling. Higher relative humidity enhances particle growth. The amount of relative humidity has a similar, but lesser, effect on EASA loss of Pt-Co as observed for Pt-only cathode catalysts. Microstructural evaluation of pre- and post-aged MEAs improves the ability to develop direct correlations between MEA microstructure and performance, determine optimal catalyst compositions, elucidate contributing MEA degradation and/or failure mechanisms, and provide feedback for MEA optimization.
Nitrided Metallic Bipolar Plates
In this approach, an electrically-conductive and corrosion-resistant Cr-nitride surface layer is formed by heating a specially designed alloy to high temperatures in a nitrogen-containing environment. Nitridation forms pin-hole defect-free protective nitride surface coatings.
Development of Alternative, Low-Cost, & Durable High Performance Cathode Supports for PEM Fuel Cells A synthesis protocol was established for preparation of mesoporous carbon with pore size of about 8 nm (left). No destruction of mesopore structures was observed during graphitization. A considerable reduction of micropore volumes through graphitization at 2600ºC was observed. The thermogravimetric analysis characterization indicates that the graphitized mesoporous carbon loaded with Pt nanoparticles is considerably more stable than commercial carbon materials loaded with Pt nanoparticles. Initial experiments were also planned to explore the feasibility of synthesis of WC-doped mesoporous carbon via cosynthesis methodology. The initial characterization indicates that no significant structure change was observed upon doping of WC into mesostructures.
Advanced Cathode Catalysts for Fuel Cells
Polymer Electrolyte/Polyvinylidene Fluoride (PVDF) Blend Membranes
Water Transport Exploratory Studies
Non-Pt Bimetallic Cathode Electrocatalysts
Graphite-Based Thermal Management System Components for Fuel Cells Fuel cell vehicles require systems capable of managing heat flow among components that require cooling (e.g., air compressor, water recovery condenser, fuel cell stack) and components that require heating for operation (e.g., water vaporizers). The low density and thermal properties of graphite have prompted efforts to use this material for components such as heat exchangers, condensers and vaporizers. Graphite fibers are low density, demonstrate high thermal conductivity, have outstanding mechanical properties, are commercially availability, and can be woven to produce lightweight 3-D structures using standard textile technologies. The geometry and scale of the woven structure can be determined in order to minimize pressure drop (below).
A new test rig was designed to measure permeability and pressure drop across structures woven by 3-Tex, Inc. and to measure heat transfer across carbon fiber weaves containing metal tubing. These results were used to design graphite woven structures that optimize heat transfer, cost and pressure drop. Modeling determined that only fibers oriented perpendicular to tubing carried heat, prompting the use of lower cost fibers elsewhere. Testing also has indicated the single metal tubes work as well as the triple tubes and that larger tubes were needed to increase water flow through the structures to increase heat transfer. It was found that the heat transfer between the copper tubing and the fibers could be increased by 25% by using thermally conductive epoxies.
Carbon Catalysts Remove Sulfur to Clean Fuel Cell Feed Gases
Several properties such as precursor nature, impurity content and type, pore structure, and surface functionality have been found to contribute to the catalytic properties of the carbon materials. The catalytic activity of the carbons are correlated to their microstructure, the amount of oxygen-containing groups on the surface, and nitrogen content. Optimization of the activity and selectivity was carried out by introduction of catalytically active nitrogen into the catalyst structure to further improve the adsorption capacity of this carbon for H2S.
Intra-Fuel Cell Diagnostics Map Dynamics of Fuel Cell Operations
Spatially resolved capillary-inlet mass spectrometry (SpaciMS) is a candidate species diagnostic for making minimally invasive intra- and inter-stack measurements within fuel cells. The instrument is based on direct capillary sampling to a residual gas analyzer. Capillaries are directly mounted in the bipolar-plate channels, blocking less than 3% of the flow path and sampling at approximately 10 ÿL /min. The SpaciMS measurement methodology is relatively easy to configure and implement, and is thus accessible to the entire fuel-cell community. SpaciMS measurements of species including oxygen, nitrogen and water at several positions across the flow path were made at realistic humidity levels in proton exchange membrane (PEM) fuel cells. This is the first such demonstration of a diagnostic that is sufficiently minimally invasive as to allow measurements throughout an operating fuel cell stack. These measurements demonstrated the relationship between fuel cell output power and oxygen consumption along the cathode serpentine flow path.
Miniature Sensors Used to Develop Improved PEM Fuel Cell Systems
The ORNL miniature sensor suite provides intra-fuel cell diagnostics within operating fuel cells. A multi-channel measurement platform, developed to enable mapping conditions within the gas diffusion layer (GDL) of a membrane electrode assembly, provides the capability to measure temperature (see ruby sphere temperature sensor above) and moisture distributions as well as species concentrations during operation. Recent developments with fiber optic sensors, combined with luminescence technology, provide the potential for minimally invasive (<100 micron) temperature distribution measurement and thermal mapping. Humidity can be determined by combining a direct measurement of water concentration within the GDL region with temperature. Temperature and humidity measurements can provide a means to validate theoretical design models of stack performance. ORNL has demonstrated the ability to characterize fuel cell thermal profile, reactant concentrations, and water distribution during operation.
The Use of Graphite Foam for Thermal Management in On-Board Fuel Reforming Processors (FASTER)
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Examination of the aging of membrane electrode assembly (MEA) materials under load is critical to the evaluation of their durability in fuel cell environments. This project uses high-resolution imaging and compositional/chemical analysis techniques for characterization of the material constituents of as-processed and electrochemically-aged PEM fuel cell MEAs. The use of advanced characterization techniques is possible due to improvements in specimen preparation including the use of “partial-embedding” for microtomy (left) and cryo-microtomy/cryo-transfer for membrane analysis in FEG -TEM. 
One of the most expensive components of a fuel cell is the bipolar plate, which electrically connects individual fuel cells in a stack to achieve a useful voltage. The use of metallic alloys for these plates would offer several benefits such as low-cost/high-volume manufacturing, high thermal and electrical conductivities, and the ability to be made into thin sheets to achieve high power densities. The inadequate corrosion resistance of most metals, however, has prevented their use. The goal of this effort is to scale-up and demonstrate the viability of thin stamped metallic bipolar plates protected by a thermal (gas) nitridation surface treatment (left). 
Poor durability of cathode supports and catalysts in proton exchange membrane fuel cells is a key technical barrier. The corrosion of carbon supports poses significant concerns at high electrode potentials and is accelerated during start/stop cycles and during higher temperature operation (>100°C). Graphitized supports perform better, but still demonstrate insufficient corrosion resistance. The goal of this project is to develop and evaluate new classes of alternative and durable high-performance cathode supports which will be highly stable, use less Pt, have high electrical conductivities, and resist corrosion.
Fuel cell catalysts are very sensitive to impurities in fuels such as sulfur and may require the use of high-purity hydrogen feedstocks. Sulfur in H2 feed supplies poisons fuel cell catalysts; concentrations as low as a few ppm of hydrogen sulfide can dramatically shorten catalyst life. A process based on the selective catalytic oxidation of H2S to elemental sulfur could remove H2S to the parts-per-billion (ppb) level at temperatures below 200°C. This project developed an improved activated carbon catalyst that can selectively oxidize H2S in H2-rich gas streams without consumption of H2, and prevents the formation of unwanted gaseous sulfur by-products, such as sulfur dioxide (SO2) and carbonyl sulfide (COS).
Improved fuel cell efficiencies can be realized through detailed understanding of the chemical and physical processes during operation. Intra-fuel cell measurements that resolve transient species concentration distributions across, and within, cells are required to understand operating details, validate reactor models and optimize system design and efficiency. Intra-reactor measurements allow higher order optimization that considers factors such as the distribution and transport of reactants and products, localized and possibly dynamic active-site blocking, and membrane degradation. 
Accurate, reliable and fast-responding sensors are a critical need for advanced fuel cell designs. Thermal, moisture and reactant concentration gradients play a key role in determining the durability and response of a fuel cell. Real-time diagnostic sensors will allow designers to increase stack power density by reducing operating margins and quickly identify the development of thermo-chemical upsets that limit performance or reduce operating lifetime.
A collaborative effort has been undertaken with DOE Laboratories to demonstrate the feasibility of on-board fuel processing for automotive fuel cell systems. The goal of the FASTER project is to design, build, and demonstrate an annular fuel processor that can start up within 60 seconds and generate reformate gas consisting of greater than 30% hydrogen and less than 50 ppm carbon monoxide. The FASTER project is led by Argonne National Laboratory. Pacific Northwest National Laboratory is providing a microchannel heat exchanger for the fuel reformer. Los Alamos National Laboratory is providing preferential oxidation (PrOx) reactors for the removal of carbon monoxide, and the Oak Ridge National Laboratory is providing five carbon foam heat exchangers for the water gas shift (WGS) and PrOx reactors.