Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “impact”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Integrated Reference Electrodes in Anion-Exchange-Membrane Electrolyzers: Impact of Stainless-Steel Gas-Diffusion Layers and Internal Mechanical Pressure

Alkaline-membrane electrolyzers operating in pure water might provide scalable low-cost H 2 production but currently lag in performance and durability compared to commercial technologies. Typically, membrane–electrode assemblies (MEAs) are optimized in electrolyzers by changing one parameter at a time and assessing the resulting system performance via two-electrode polarization and impedance measurements. These approaches are limited in their ability to assign performance changes and durability to specific electrodes or processes. We integrate a reference electrode with the MEA to separate anode and cathode responses in both polarization and impedance measurements. Here we illustrate the power of the approach by showing how the fiber diameter of stainless-steel gas-diffusion layers (GDLs) affects performance solely at the anode, while changing the thickness of the cathode GDL simultaneously affects the performance of the anode and cathode due to changes in internal pressure from mechanical compression. This finding was obscured in conventional two-electrode measurements. The work thus guides both high-performance alkaline-membrane water-electrolyzer development and illustrates a useful strategy to study structure–activity relationships in the MEA.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Structural Defects of Silver Hollandite, Ag x Mn 8 O y , Nanorods: Dramatic Impact on Electrochemistry

Hollandites (OMS-2) are an enticing class of sorbents, catalysts, and energy storage materials with a tunnel structure permitting one-dimensional insertion and deinsertion of ions and small molecules along the c direction. A 7-fold increase in delivered capacity for Li/Ag x Mn 8 O 16 electrochemical cells (160 versus 23 mAh/g) observed upon a seemingly small change in silver content ( x ~1.1 (L-Ag-OMS-2) and 1.6 (H-Ag-OMS-2)) led us to characterize the structure and defects of the silver hollandite material. In this work, Ag hollandite nanorods are studied through the combined use of local (atomic imaging, electron diffraction, electron energy-loss spectroscopy) and bulk (synchrotron based X-ray diffraction, thermogravimetric analysis) techniques. Selected area diffraction and high resolution transmission electron microscopy show a structure consistent with that refined by XRD; however, the Ag occupancy varies significantly even within neighboring channels. Both local and bulk measurements indicate a greater quantity of oxygen vacancies in L-Ag-OMS-2, resulting in lower average Mn valence relative to H-Ag-OMS-2. Electron energy loss spectroscopy shows a lower Mn oxidation state on the surface relative to the interior of the nanorods, where the average Mn valence is approximately Mn 3.7+ for H-Ag-OMS-2 and Mn 3.5+ for L-Ag-OMS-2 nanorods, respectively. The higher delivered capacity of L-Ag-OMS-2 may be related to more oxygen vacancies compared to H-Ag-OMS-2. Thus, the oxygen vacancies and MnO 6 octahedra distortion are assumed to open the MnO 6 octahedra walls, facilitating Li diffusion in the ab plane. These results indicate crystallite size and surface defects are significant factors affecting battery performance.

25 ENERGY STORAGE↗
DOE OSTI2014

The Impact of Fullerene Structure on Its Miscibility with P3HT and Its Correlation of Performance in Organic Photovoltaics

Neutron reflectivity experiments are utilized to obtain the miscibility limit of four different fullerenes, bis-PCBM, ICBA, thio-PCBM, and PC70BM, in poly(3-hexylthiophene) (P3HT). The intermixing of P3HT and fullerene bilayers is monitored by neutron reflectivity before and after thermal annealing, providing quantification of the miscibility and interdiffusion of the fullerene within P3HT. These results indicate that the miscibility limit of these fullerenes in P3HT ranges from 11% to 26%, where the bis-adduct fullerenes exhibit lower miscibility in P3HT, which is also verified by small angle neutron scatting (SANS). The in-plane morphology of the P3HT:fullerene mixtures was also examined by SANS, which shows a decrease in domain size and an increase in the specific interfacial area between the fullerene and the polymer with the bis-fullerenes. Correlation of miscibility and morphology to device performance indicates that polymer/ fullerene miscibility is crucial to rationally optimize the design of fullerenes for use in organic photovoltaics. Bis-PCBM has a higher open circuit voltage (Voc) than PC60BM with P3HT; however, device performance of bis-PCBM based devices is lower than that of PC60BM based devices. This decrease in performance is attributed to the lower miscibility of bis-PCBM in P3HT, which decreases the probability of exciton dissociation and enhances the recombination of free charge carriers in the miscible region. Moreover, the minimum distance between fullerenes in the miscible region to facilitate intermolecular transport is identified as 11 .

Chen, Huipeng↗