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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 1,657 records · Page 92
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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 OSTI2014

Impact of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Reaction Activity for Platinum Electrocatalysts

The impact of model membrane degradation compounds on the relevant electrochemical parameters for the oxygen reduction reaction (i.e. electrochemical surface area and catalytic activity), was studied for both polycrystalline Pt and carbon supported Pt electrocatalysts. Model compounds, representing previously published, experimentally determined polymer electrolyte membrane degradation products, were in the form of perfluorinated organic acids that contained combinations of carboxylic and/or sulfonic acid functionality. Perfluorinated carboxylic acids of carbon chain length C1 – C6 were found to have an impact on electrochemical surface area (ECA). The longest chain length acid also hindered the observed oxygen reduction reaction (ORR) performance, resulting in a 17% loss in kinetic current (determined at 0.9 V). Model compounds containing sulfonic acid functional groups alone did not show an effect on Pt ECA or ORR activity. Lastly, greater than a 44% loss in ORR activity at 0.9V was observed for diacid model compounds DA-Naf (perfluoro(2-methyl-3-oxa-5-sulfonic pentanoic) acid) and DA-3M (perfluoro(4-sulfonic butanoic) acid), which contained both sulfonic and carboxylic acid functionalities.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2016

Polybenzimidazole (PBI) functionalized nanographene as highly stable catalyst support for polymer Electrolyte membrane fuel cells (PEMFCs)

Nanoscale graphenes were used as cathode catalyst supports in proton exchange membrane fuel cells (PEMFCs). Surface-initiated polymerization that covalently bonds polybenzimidazole (PBI) polymer on the surface of graphene supports enables the uniform distribution of the Pt nanoparticles, as well as allows the sealing of the unterminated carbon bonds usually present on the edge of graphene from the chemical reduction of graphene oxide. The nanographene effectively shortens the length of channels and pores for O 2 diffusion/water dissipation and significantly increases the primary pore volume. Further addition of p-phenyl sulfonic functional graphitic carbon particles as spacers, increases the specific volume of the secondary pores and greatly improves O 2 mass transport within the catalyst layers. The developed composite cathode catalyst of Pt/PBI-nanographene (50 wt%) + SO 3 H-graphitic carbon black demonstrates a higher beginning of life (BOL) PEMFC performance as compared to both Pt/PBI-nanographene (50 wt%) and Pt/PBI-graphene (50 wt%) + SO 3 H-graphitic carbon black (GCB). Accelerated stress tests show excellent support durability compared to that of traditional Pt/Vulcan XC72 catalysts, when subjected to 10,000 cycles from 1.0 V to 1.5 V. As a result, this study suggests the promise of using PBI-nanographene + SO 3 H-GCB hybrid supports in fuel cells to achieve the 2020 DOE targets for transportation applications.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2013

Analysis of SOFCs Using Reference Electrodes

Reference electrodes are frequently applied to isolate the performance of one electrode in a solid oxide fuel cell. However, reference electrode simulations raise doubt to veracity of data collected using reference electrodes. The simulations predict that the reported performance for the one electrode will frequently contain performance of both electrodes. Nonetheless, recent reports persistently treat data so collected as ideally isolated. This work confirms the predictions of the reference electrode simulations on two SOFC designs, and to provides a method of validating the data measured in the 3-electrode configuration. Validation is based on the assumption that a change in gas composition to one electrode does not affect the impedance of the other electrode at open circuit voltage. This assumption is supported by a full physics simulation of the SOFC. Three configurations of reference electrode and cell design are experimentally examined using various gas flows and two temperatures. Impedance data are subjected to deconvolution analysis and equivalent circuit fitting and approximate polarization resistances of the cathode and anode are determined. The results demonstrate that the utility of reference electrodes is limited and often wholly inappropriate. Reported impedances and single electrode polarization values must be scrutinized on this basis.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2016

Stable electrolyte for high voltage electrochemical double-layer capacitors

A simple electrolyte consisting of NaPF 6 salt in 1,2-dimethoxyethane (DME) can extend the voltage window of electric double-layer capacitors (EDLCs) to >3.5 V. DME does not passivate carbon electrodes at very negative potentials (near Na/Na + ), extending the practical voltage window by about 1.0 V compared to standard, non-aqueous electrolytes based on acetonitrile. The voltage window is demonstrated in two- and three-electrode cells using a combination of electrochemical impedance spectroscopy (EIS), charge-discharge cycling, and measurements of leakage current. DME-based electrolytes cannot match the high conductivity of acetonitrile solutions, but they can satisfy applications that demand high energy density at moderate power. The conductivity of NaPF 6 in DME is comparable to commercial lithium-ion battery electrolytes and superior to most ionic liquids. Lastly, factors that limit the voltage window and EDLC energy density are discussed, and strategies to further boost energy density are proposed.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2017

Galvanostatic Intermittent Titration and Performance Based Analysis of LiNi 0.5 Co 0.2 Mn 0.3 O 2 Cathode

Galvanostatic intermittent titration technique (GITT) - a popular method for characterizing kinetic and transport properties of battery electrodes - is predicated on the proper evaluation of electrode active area. LiNi 0.5044 Co 0.1986 Mn 0.2970 O 2 (NCM523) material exhibits a complex morphology in which sub-micron primary particles aggregate to form secondary particle agglomerates. Our work proposes a new active area formulation for primary/secondary particle agglomerate materials to better mimic the morphology of NCM532 electrodes. Furthermore, this formulation is then coupled with macro-homogeneous models to simulate GITT and half-cell performance of NCM523 electrodes. Subsequently, the model results are compared against the experimental results to refine the area formulation. A single parameter, the surface roughness factor, is proposed to mimic the change in interfacial area, diffusivity and exchange current density simultaneously and detailed modeling results are presented to provide valuable insights into the efficacy of the formulation.

25 ENERGY STORAGE↗