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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Plasma deposition and surface modification techniques for wear resistance

The ion-assisted or plasma coating technology is discussed as it applies to the deposition of hard, wear resistant refractory compound films. Of the many sputtering and ion plating modes and configurations the reactive magnetron sputtering and the reactive triode ion plating techniques are the preferred ones to deposit wear resistant coatings for tribological applications. Both of these techniques incorporate additional means to enhance the ionization efficiency and chemical reaction to precision tailor desirable tribological characteristics. Interrelationships between film formation, structure, and ribological properties are strictly controlled by the deposition parameters and the substrate condition. The enhanced ionization contributes to the excellent adherence and coherence, reduced internal stresses and improved structural growth to form dense, cohesive, equiaxed grain structure for improved wear resistance and control.

Spalvins, T.↗
DOE OSTI2020

Boosting alkaline hydrogen evolution: the dominating role of interior modification in surface electrocatalysis

The alkaline hydrogen evolution reaction (A-HER) holds great promise for clean hydrogen fuel generation but its practical utilization is severely hindered by the sluggish kinetics for water dissociation in alkaline solutions. Traditional ways to improve the electrochemical kinetics for A-HER catalysts have been focusing on surface modification, which still can not meet the demanding requirements for practical water electrolysis because of catalyst surface deactivation. In this work, we report an interior modification strategy to significantly boost the A-HER performance. Specifically, a trace amount of Pt was doped in the interior Co 2 P (Pt–Co 2 P) to introduce a stronger dopant–host interaction than that of the surface-modified catalyst. Consequently, the local chemical state and electronic structure of the catalysts were adjusted to improve the electron mobility and reduce the energy barriers for hydrogen adsorption and H–H bond formation. As a proof-of-concept, the interior-modified Pt–Co 2 P shows a reduced onset potential at near-zero volts for the A-HER, low overpotentials of 2 mV and 58 mV to achieve 10 and 100 mA cm –2 , and excellent durability for long-term utilization. The interior-modified Pt–Co 2 P delivers superior A-HER performance to Pt/C and other state-of-the-art electrocatalysts. This work will open a new avenue for A-HER catalyst design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Bioinspired nonwetting surfaces for corrosion inhibition over a range of temperature and corrosivity

Applications of superhydrophobic (SHS) and lubricant infused surfaces (LIS) involve exposure to corrosive environments from the acidic to the basic, at a range of temperatures, that are not fully characterized. Here, we present for the first time a multifactorial study of the effects of surface fabrication method, surface modification, surface functionalization time, temperature and pH of the immersion medium on the corrosion performance of nonwetting copper surfaces. Bioinspired SHS and LIS fabricated using facile methods of etching and electrodeposition are systematically assessed using potentiodynamic polarization measurements for their corrosion resistance in saline solution (pH ≈7) over a temperature range 23–85°C. SHS and LIS are shown to exhibit diminished corrosion rate, by up to two orders of magnitude, compared to bare copper surface. An Arrhenius model is developed for the first time, describing the temperature- dependent corrosion rate of SHS and LIS. Electrochemical impedance spectroscopy is used to show that corrosion resistance of LIS is larger by three orders of magnitude in extremely acidic (pH = 1) and by an order magnitude in extremely alkaline (pH = 14) media compared to bare copper surface. Etched LIS are generally more resistant to corrosion compared to SHS at all temperatures with excellent microstructural durability.

42 ENGINEERING↗
DOE OSTI2025

Engineering surface charges of nanofiltration membranes to maximize Li + /Mg 2+ separation properties

Polyamide-based nanofiltration (NF) membranes are attractive for Li + /Mg 2+ separation for lithium recovery from salt brine (containing mainly Mg 2+ ). However, Li + and Mg 2+ have similar hydration radii, resulting in a low separation factor (SF Li/Mg ). Herein, we demonstrate that SF Li/Mg can be significantly enhanced by optimizing the membrane surface positive charges. This results in an unexpected maximum SF Li/Mg at a solution pH slightly below its isoelectric point (IEP). Specifically, NF270 membrane was surface-grafted with 2-(methacryloyloxy)ethyltrimethylammonium chloride (META) or polyethylenimine (PEI) using bio-adhesive dopamine, forming a thin, stable, charged layer (20–40 nm) on the surface. The effects of solution pH and surface modification on the surface zeta potential (ZP) and single- and mixed-salt Li + /Mg 2+ separation properties are thoroughly investigated. For example, the META grafting increases the ZP from 9.2 to 16 mV and SF Li/Mg by 130 % from 35 to 80 at pH 4, superior to the state-of-the-art commercial NF membranes. Furthermore, this surface modification occurs at ≈22 °C in aqueous solutions and can be utilized to enhance commercial modules for practical applications.

Li+/Mg2+ separation↗
DOE OSTI2020

Enabling electrochemical N 2 reduction to NH 3 in the low overpotential region using non-noble metal Bi electrodes via surface composition modification

The electrochemical N 2 reduction reaction (ENRR) that can produce NH 3 using water as the hydrogen source at ambient temperature and pressure can be an exciting alternative to the Haber–Bosch process. The major challenge for electrochemical NH 3 production is the competing hydrogen evolution reaction (HER), which seriously limits the faradaic efficiency (FE) for NH 3 production. To date, noble metal electrocatalysts that are inactive for the HER have mainly been investigated for the ENRR. Studies reporting a FE greater than 10% for NH 3 production using non-noble metal catalysts in the low overpotential region (E ≤ 0.2 V vs. RHE) are very rare. This study reports effective electrochemical surface modification strategies that drastically increase the ENRR activity of a non-noble Bi electrode in the low overpotential region and achieve a FE for NH 3 production as high as 13.2% at -0.2 V vs. RHE in pH 7.5 phosphate buffer. Finally, the effect of each of the surface modifications on the activity for the ENRR and the electrode stability during the ENRR were systematically elucidated, which may be used to develop general strategies to enhance the ENRR activities of other non-noble metal electrodes in the low overpotential region.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗