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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Improving Durability of Fuel Cells with Platinum-rich Alloy Cathode Catalysts

Pt 3 Co-alloy based nanoparticle catalysts are very active for oxygen reduction reaction (ORR) thereby enabling high performance of proton exchange membrane fuel cells (PEMFC) for automotive propulsion. However, these catalyst materials degrade due to a combination of electrochemical surface area (ECSA) loss and dissolution of cobalt-alloying element from the nanoparticles. Dissolution of cobalt has a two-fold impact on the durability of fuel cells—i) a loss in the low-current density kinetic region due to a decrease in specific activity and ii) a loss in the high-current density transport region due to Co 2+ contamination of the ionomer phase. Cobalt dissolution-contamination needs to be mitigated as it limits fuel cell performance and lifetime for heavy-duty automotive applications. In this article, we study the use of PtCo-alloy catalysts with Pt-rich compositions using catalyst-specific accelerated stress test measurement in membrane electrode assemblies to decrease the amount of dissolved Co and mitigate its subsequent contamination effects. We demonstrate Pt 5 Co and Pt 7 Co compositions to enable significant improvements in durability (∼50 mV and ∼100 mV with respect to Pt 3 Co after 30,000 voltage cycles) with a minor but acceptable compromise in the initial specific activity of the catalyst.

08 HYDROGEN↗
DOE OSTI2023

Do Melamine and Melamine-Formaldehyde Surface Modifiers Improve Fuel Cell Activity and Durability?

Precious group metal-based catalysts based on Pt- and Pt-alloys are currently used as catalysts for the kinetically sluggish Oxygen Reduction Reaction (ORR) on the cathode of fuel cells. The activity of Pt or Pt-alloy catalysts towards ORR is severely compromised by the adsorption of spectator-species such as sulfonate anions from perfluorosulfonic acid (PFSA) ionomer or Pt-O(H) ad via water activation. Considering recent evidence pointing to the improvement in ORR activity via the use of melamine organic molecule or melamine-formaldehyde copolymeric additives as surface blocking agents for the prevention of sulfonate or Pt-OH ad adsorption, we evaluated these additives in fuel cells. The catalysts were modified with either of these additives and characterized using ex situ and in situ methods to verify successful adsorption and eventual performance in fuel cells. These surface modifying agents were found to suppress Pt-OH ad formation as well as suppress ORR activity. There was no evidence to point out that these additives improved ORR activity and H 2 /air polarization performance in a fuel cell MEA on supported, polycrystalline Pt catalyst.

08 HYDROGEN↗
DOE OSTI2018

Durability of Pt-Co Alloy Polymer Electrolyte Fuel Cell Cathode Catalysts under Accelerated Stress Tests

The durability of Pt-Co alloy cathode catalysts supported on high surface area carbon is investigated by subjecting them to accelerated stress tests (ASTs). The catalysts had different initial Co contents and nanoparticle morphologies: a “spongy” porous morphology for the high-Co (H) content catalyst, and a fully alloyed crystalline morphology for the medium-Co (M) and low-Co (L) content catalysts. The specific activity of the catalysts depends on their initial Co content, morphology and nanoparticle size, and remained higher than 1000 μA/cm 2 -Pt after 27–50% Co loss. The H-catalyst electrode showed the smallest kinetic overpotentials (η c s ) due to higher initial Pt loading than the other two electrodes, but it had the fastest increase in ηcs with AST cycling due to lower Co retention; the L-catalyst electrode showed higher η c s due to a lower initial Pt loading, but had a smaller increase in η c s with aging due to higher Co retention; the M-catalyst electrode showed a similar increase in η c s with aging, but this increase was due to the combined effects of Co dissolution and electrochemically active surface area (ECSA) loss. In conclusion, the modeled increase in mass transfer overpotentials with aging correlates with the initial Pt loading, ECSA loss and the initial catalyst morphology

25 ENERGY STORAGE↗
DOE OSTI2018

Accelerated Stress Testing of Fuel Cell Membranes Subjected to Combined Mechanical/Chemical Stressors and Cerium Migration

A highly accelerated stress test (HAST) has been developed to generate local stressful conditions that are representative of those in automotive fuel cell stacks. Using a 50-cm 2 cell cycled between 0.05 and 1.2 A/cm 2 with a low inlet RH in the co-flow configuration, the HAST creates a distribution of combined mechanical/chemical stressors in the membrane with the maximum chemical stress occurring near the gas inlets and the maximum mechanical stress near the outlets. Conducting HASTs using a current distribution measurement tool and a shorting/crossover diagnostic method to track the state of health of a robust membrane containing both a mechanical support and a chemical stabilizing additive, the result shows that the membrane location with the most severe thinning coincides with that of the deepest membrane hydration cycling. Upon examination of the cerium redistribution patterns after the test, it was found that the severe humidity cycling generated by the HAST condition near the outlet region not only generated the highest membrane mechanical stress but also resulted in the strongest water flux, which may cause local depletion of the cerium added as chemical stabilizer. Further study is required to decouple the cerium migration effect from the possible mechanical/chemical synergistic degradation effect.

25 ENERGY STORAGE↗
DOE OSTI2018

Enhanced Oxygen Reduction Reaction Activity on Pt-Monolayer-Shell PdIr/Ni-Core Catalysts

Platinum monolayer oxygen reduction reaction catalysts offer the most promising possibility of reducing the Pt content without sacrificing its fuel cell performance. Here, we present a facile way of preparing Pt monolayer shell on PdIr-based core catalysts with and without Ni sub-core. They showed much higher activity for oxygen reduction reaction than commercial Pt/C catalyst. Among tested samples, PtMLPd2Ir/Ni/C performs the best having Pt mass activity 14 times and Platinum Group Metal mass activity 0.8 times higher than that of Pt/C. In addition, accelerated durability test indicates its excellent durability, which was demonstrated by a 7.5% decrease in Platinum Group Metal mass activity compared to 64% for the commercial Pt/C catalyst. As a result, the role of Ni sub-core in oxygen reduction reaction activity and durability of PtML on PdIr-based catalysts was also elucidated.

25 ENERGY STORAGE↗
DOE OSTI2019

Performance of Polymer Electrolyte Fuel Cell Electrodes with Atomically Dispersed (AD) Fe-C-N ORR Catalyst

Activity of (AD)Fe-N-C catalyst with low Fe content is investigated in differential cells prepared by hot pressing anode gas diffusion electrodes (0.2 mgPt/cm2) to N211 membrane and brush painting the cathode catalyst ink. Polarization curves obtained in H2/O2 show double Tafel slopes which, in conjunction with the redox potential observed in cyclic voltammetry traces, forms the basis for a distributed ORR (oxygen reduction reaction) kinetic model with potential-dependent available sites. Application of this model to polarization data in H2/air provides the basis for formulating an oxygen transport model and leads to 7.7 ± 0.6 mA/cm2 catalyst activity at 0.9 V, 31.5-34.3 mA/cm2 cell performance at 0.8 V, and 0.8-2 s/cm O2 transport resistance. A coupled kinetic, O2 transport and proton transport illustrates the projected improvements needed in catalyst activity and electrode structure to approach the automotive target of 1000 mW/cm2 stack power density while meeting the 1.45 kW/oC heat rejection constraint at 1.5 cathode stoichiometry. The model indicates that we need twelve-fold higher mass activity for reducing the kinetic losses, doubling of active site density and an engineered electrode structure for 50% lower proton transport resistance, as well as a 50% reduction in electrode thickness to limit the O2 transport losses

ACTIVE-SITES↗
DOE OSTI2017

Experimental and Theoretical Analysis of Ink Dispersion Stability for Polymer Electrolyte Fuel Cell Applications

The aggregate size in fuel cell catalyst inks depends on the type of dispersion medium, particle concentration, and addition of stabilizing agents. In this work, ink stability and particle size of carbon black and carbon black/Nafion dispersions in four non-aqueous media, viz., methanol, ethanol, isopropanol and ethyl acetate are studied. Based on visual inspection, isopropanol is found to be the best medium for dispersion of carbon black inks. To rationalize this observation, a semi-empirical model based on diffusion-limited aggregation was developed to evaluate the rate of particle aggregation and predict the ink stability time for each dispersion medium. The proposed model supports the experimental observation by qualitatively predicting the same relationship between carbon stability and the dispersion media. The model also showed that the dielectric constant of the dispersion medium and the particle zeta potential are primarily responsible for the ink stability. Particle size for the different inks was determined by dynamic light scattering with and without dilution. Experimental results show that Nafion is a strong stabilizing agent, increasing the ink stability and decreasing the particle size of carbon aggregates. The beneficial effects of Nafion are independent of its concentration and are observed even at Nafion volume fractions of 10 wt%. The interaction energy is found to be a strong function of the surface potential for the dispersion medium with a higher dielectric constant.

25 ENERGY STORAGE↗
DOE OSTI2016

Fabrication of High Performing PEMFC Catalyst-Coated Membranes with a Low Cost Air-Assisted Cylindrical Liquid Jets Spraying System

In this paper, a low cost air-assisted cylindrical liquid jets spraying (ACLJS) system was developed to prepare high-performance catalyst-coated membranes (CCMs) for proton exchange membrane fuel cells (PEMFCs). The catalyst ink was flowed from a cylindrical orifice and was atomized by an air stream fed from a coaxial slit and sprayed directly onto the membrane, which was suctioned to a heated aluminum vacuum plate. The CCM pore architecture including size, distribution and volume can be controlled using various flow parameters, and the impact of spraying conditions on electrode structure and PEMFC performance was investigated. CCMs fabricated in the fiber-type break-up regime by ACLJS achieved very high performance during PEMFC testing, with the top-performing cells having a current density greater than 1900 mA/cm 2 at 0.7 V under H 2 /O 2 flows and 700 mA/cm 2 under H 2 /Air at 1.5 bar(absolute) pressure and 60% gas RH, and 80°C cell temperature.

25 ENERGY STORAGE↗
DOE OSTI2021

Hydrogen: Targeting $1/kg in 1 Decade

The societal energy system is evolving rapidly as the impacts of our existing energy system are better appreciated and technological advances have dramatically decreased the cost of renewable resources. Simultaneously, the importance of energy transfer across timeframes and the difficulty of decarbonizing the industrial loads and transportation demands using electricity are being recognized. At the center of this need is achieving low-cost clean hydrogen. The U.S. Department of Energy launched the Hydrogen Energy EarthShot which seeks to reduce the cost of clean hydrogen to $1 per 1 kilogram in one decade. Reaching the $1/kg goal is dependent on the evolution of the electrical energy system to increase renewable energy deployment and low electricity costs; advances in electrolysis technology and manufacturing readiness; and infrastructure build-out and hydrogen market establishment that results in the ability to make, move, store, and use clean hydrogen economically while spurring job creation.

08 HYDROGEN↗
DOE OSTI2023

LTE-P-20 Water Content

A procedure to determine the percent of water content of membrane. The SOP was prepared by Chris Capuano.

Electrolyzer↗
DOE OSTI2014

Strategies for Probing Nanometer-Scale Electrocatalysts: From Single Particles to Catalyst-Membrane Architectures

The project primary objectives are to prepare and elucidate the promoting properties of materials that possess high activity for the conversion of hydrogen and related small molecules (water, oxygen, carbon monoxide and methanol) in polymer electrolyte fuel cells. One area of research has focused on the study of catalyst materials. Protocols were developed for probing the structure and benchmarking the activity of Pt and Pt bimetallic nanometer-scale catalyst against Pt single crystal electrode standards. A second area has targeted fuel cell membrane and the advancement of simple methods mainly based on vibrational spectroscopy that can be applied broadly in the study of membrane structure and transport properties. Infrared and Raman methods combined with least-squares data modeling were applied to investigate and assist the design of robust, proton conductive membranes, which resist reactant crossover.

08 HYDROGEN↗
DOE OSTI2014

Durability of Low Platinum Fuel Cells Operating at High Power Density

Understanding and improving the durability of cost-competitive fuel cell stacks is imperative to successful deployment of the technology. Stacks will need to operate well beyond today’s state-of-the-art rated power density with very low platinum loading in order to achieve the cost targets set forth by DOE ($\$$15/kW) and ultimately be competitive with incumbent technologies. An accelerated cost-reduction path presented by Nuvera focused on substantially increasing power density to address non-PGM material costs as well as platinum. The study developed a practical understanding of the degradation mechanisms impacting durability of fuel cells with low platinum loading (≤0.2mg/cm 2 ) operating at high power density (≥1.0W/cm 2 ) and worked out approaches for improving the durability of low-loaded, high-power stack designs.

08 HYDROGEN↗