Search NASA⌕ Search

Engineering topics

Chen, Yu

Publications and source records attributed to Chen, Yu.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

An improved oxygen reduction reaction activity and CO 2 -tolerance of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ achieved by a surface modification with barium cobaltite coatings

Solid oxide fuel cells (SOFCs) cathode often suffers from the poisoning effect of the contaminants commonly encountered in air such as CO 2 . Here we report an effective approach to enhancing the activity and CO 2 tolerance of the state-of-the-art La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) cathode enabled by a coating of BaCoO 3-δ (BCO), as verified by the electrochemical testings, Raman analyses, and density functional theory calculations. When surface modified with a thin-film BCO coating, LSCF displays a much enhanced ORR activity and an improved durability against CO 2 . For example, anode supported SOFCs with the LSCF cathode coated with BCO coatings show a remarkable peak power density (Pmax) of 0.41 Wcm -2 and a significantly reduced degradation rate in current density of ~0.08% h -1 at 0.8 V and 700 °C for a period of 300 hs when humidified H2 (with 3 vol%H2O) was used as fuel and air with 8 vol% CO 2 as oxidant. The demonstrated performance is improved when compared with those of the cells with a blank LSCF electrode (a Pmax of ~0.36 Wcm -2 and a degradation rate of ~0.15% h -1 ) under the same conditions. Furthermore, the adsorption energy calculations suggests that BCO coating makes CO 2 adsorption much weaker than LSCF (-0.54 eV versus -1.07 eV).

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

An Efficient Bifunctional Air Electrode for Reversible Protonic Ceramic Electrochemical Cells

One of the main bottlenecks that limits the performance of reversible protonic ceramic electrochemical cells (R-PCECs) is the sluggish kinetics of the oxygen reduction and evolution reactions (ORR and OER). Here, the significantly enhanced ORR and OER kinetics and stability of a conventional La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) air electrode by an efficient catalyst coating of barium cobaltite (BCO) is reported. The polarization resistance of a BCO-coated LSCF air electrode at 600 oC is 0.16 Ω cm 2 , about 30% of that of the bare LSCF air electrode under the same conditions. Further, a R-PCEC with the BCO-coated LSCF air electrode shows exceptional performance in both fuel cell (maximum power density of 1.16 W cm -2 at 600 ºC) and electrolysis (current density of 1.80 A cm -2 at 600 ºC at 1.3 V) modes. Finally, the performance enhancement is attributed mainly to the facilitated rate of oxygen surface exchange.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Discovery of SARS-CoV-2 Papain-like Protease Inhibitors through a Combination of High-Throughput Screening and a FlipGFP-Based Reporter Assay

The papain-like protease (PL pro ) of SARS-CoV-2 is a validated antiviral drug target. Through a fluorescence resonance energy transfer-based high-throughput screening and subsequent lead optimization, we identified several PL pro inhibitors including Jun9-72-2 and Jun9-75-4 with improved enzymatic inhibition and antiviral activity compared to GRL0617, which was reported as a SARS-CoV PL pro inhibitor. Significantly, we developed a cell-based FlipGFP assay that can be applied to predict the cellular antiviral activity of PL pro inhibitors in the BSL-2 setting. X-ray crystal structure of PL pro in complex with GRL0617 showed that binding of GRL0617 to SARS-CoV-2 induced a conformational change in the BL2 loop to a more closed conformation. Molecular dynamics simulations showed that Jun9-72-2 and Jun9-75-4 engaged in more extensive interactions than GRL0617. Overall, the PL pro inhibitors identified in this study represent promising candidates for further development as SARS-CoV-2 antivirals, and the FlipGFP-PL pro assay is a suitable surrogate for screening PL pro inhibitors in the BSL-2 setting.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Catalyst coating of a perovskite film and particles exsoluted from the perovskite film

A hybrid catalyst coating composed of a conformal thin film with exsoluted PrOx nano-particles. The conformal PNM thin film can be a perovskite composition of PrNi0.5Mn0.5O3 (PNM). The PrOx nano-particles dramatically enhance the oxygen reduction reaction kinetics via a high concentration of oxygen vacancies while the thin PNM film effectively suppresses strontium segregation from the cathode of an intermediate-temperature solid oxide fuel cell.

Liu, Meilin↗
DOE OSTI2021

Reduction in total and major cause-specific mortality from tobacco smoking cessation: a pooled analysis of 16 population-based cohort studies in Asia

Little is known about the time course of mortality reduction following smoking cessation in Asians who have smoking behaviours distinct from their Western counterparts. We evaluated the level of reduction in all-cause, cardiovascular disease (CVD) and lung cancer mortality by years since quitting smoking, in Asia. Using Cox regression, we analysed individual participant data (n = 709 151) from 16 prospective cohorts conducted in China, Japan, Korea/Singapore, and India/Bangladesh, separately by cohorts. Cohort-specific hazard ratios (HRs) were combined using a random-effects meta-analysis. During a mean follow-up of 12.0 years, 108 287 deaths were ascertained—35 658 from CVD and 7546 from lung cancer. Among Asian men, a dose-response relationship of risk reduction in deaths from all causes, CVD and lung cancer was observed with an increase in years after smoking cessation. Compared with never smokers, however, all-cause and CVD mortality among former smokers remained elevated 10–14 years after quitting [multivariable-adjusted HR (95% confidence interval (CI) = 1.25 (1.13–1.37) and 1.20 (1.02–1.41), respectively]. Lung cancer mortality stayed almost 2-fold higher than among never smokers 15–19 years after smoking cessation [1.97 (1.41–2.73)], particularly among former heavy smokers [2.62 (1.71–4.00)]. Women who quitted for ≥5 years retained a significantly elevated mortality from all causes, CVD and lung cancer. Overall patterns of the cessation-mortality associations were similar across countries. Our findings suggest that adverse effects of tobacco smoking persist for an extended time period, even for more than two decades, which is beyond the time windows defined in current clinical guidelines for risk assessment of lung cancer and CVD.

Public, Environmental & Occupational Health↗
DOE OSTI2021

Combined Effects of Fe(III)-Bearing Clay Minerals and Organic Ligands on U(VI) Bioreduction and U(IV) Speciation

Reduction of U(VI) to U(IV) drastically reduces its solubility and has been proposed as a method for remediation of uranium contamination. However, much is still unknown about the kinetics, mechanisms, and products of U(VI) bioreduction in complex systems. In this work, U(VI) bioreduction experiments were conducted with Shewanella putrefaciens strain CN32 in the presence of clay minerals and two organic ligands: citrate and EDTA. In reactors with U and Fe(III)-clay minerals, the rate of U(VI) bioreduction was enhanced due to the presence of ligands, likely because soluble Fe 3+ - and Fe 2+ -ligand complexes served as electron shuttles. In the presence of citrate, bioreduced U(IV) formed a soluble U(IV)-citrate complex in experiments with either Fe-rich or Fe-poor clay mineral. In the presence of EDTA, U(IV) occurred as a soluble U(IV)-EDTA complex in Fe-poor montmorillonite experiments. However, U(IV) remained associated with the solid phase in Fe-rich nontronite experiments through the formation of a ternary U(IV)-EDTA-surface complex, as suggested by the EXAFS analysis. Our study indicates that organic ligands and Fe(III)-bearing clays can significantly affect the microbial reduction of U(VI) and the stability of the resulting U(IV) phase.

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

Highly Stretchable, Ultratough, and Multifunctional Poly(vinyl chloride)-Based Plastics via a Green, Star-Shaped Macromolecular Additive

As one of the most prolifically produced plastics in the world, poly(vinyl chloride) (PVC) suffers from mechanical brittleness and low toughness. Compared with traditional phthalate-type plasticizers, poly(ε-caprolactone) (PCL)-based plasticizers are especially attractive due to their “green” nature and capabilities to achieve improved physical properties. Herein, a stretchable and ultratough PVC-based plastic was achieved by a star-shaped PCL copolymer with a rigid, amino-containing, branched polylactide (N-BPLA) core and a soft PCL shell, that is, RN-SPCLs. With an optimal feed ratio of the CL monomer and N-BPLA core, the RN-SPCL2 can efficiently lower the glass transition temperature (T g ) of PVC plastics, achieving the transition from the “glassy” to “rubbery” state at ambient temperature. The obtained RN-SPCL2/PVC not only shows high extensibility, that is, 453%, but also maintains close to 80% of tensile strength of neat PVC, that is, 30.1 MPa, which is much higher than the previously reported plasticized PVCs. Its overall toughness reaches 92.7 MJ/m 3 , being more than 50-fold higher than neat PVC and 2 to 3 times higher than linear PCL or dibutyl phthalate plasticized PVCs. The important role of star-shaped architecture with a rigid core and flexible PCL shell for RN-SPCL2 in achieving highly stretchable and ultratough PVC plastics is systematically investigated. More interestingly, the as-prepared RN-SPCLs also endow PVC plastics with photoluminescence property and allow homogeneous dispersion of nanosized TiO 2 for significantly enhancing the anti-UV capability.

36 MATERIALS SCIENCE↗
DOE OSTI2021

An Active and Robust Air Electrode for Reversible Protonic Ceramic Electrochemical Cells

Reversible protonic ceramic electrochemical cells (RPCECs) are a promising option for efficient and low-cost generation of electricity and hydrogen. Commercialization of R-PCECs, however, hinges on the development of highly active and robust air electrodes. Here, we report an air electrode consisting of PrBa 0.8 Ca 0.2 Co 2 O 5+δ and in situ exsolved BaCoO 3–δ nanoparticles (PBCC–BCO) that shows minimal polarization resistance (~0.24 Ω cm 2 at 600 °C) and high stability when exposed to humidified air with 3–50% H 2 O. An R-PCEC utilizing PBCC-BCO demonstrates remarkable performances at 600 °C: achieving a peak power density of 1.06 W cm –2 in the fuel cell mode and a current density of 1.51 A cm –2 at 1.3 V in an electrolysis mode. More importantly, the RPCECs demonstrate an exceptionally high durability over 1833 h of continuous operation in the electrolysis mode. Furthermore, this work offers an efficient approach to design of high-performance and durable electrodes for R-PCECs.

25 ENERGY STORAGE↗
DOE OSTI2021

Enhancing Oxygen Reduction Activity and Cr Tolerance of Solid Oxide Fuel Cell Cathodes by a Multiphase Catalyst Coating

Intermediate temperature solid oxide fuel cells (IT-SOFCs) are cost-effective and efficient energy conversion systems. Here, the sluggish oxygen reduction reaction (ORR) and the degradation of cathodes are critical challenges to the commercialization of IT-SOFCs. Here, a highly efficient multiphase (MP) catalyst coating, consisting of Ba 1–x Co 0.7 Fe 0.2 Nb 0.1 O 3–δ (BCFN) and BaCO 3 , to enhance the ORR activity and durability of the state-of-the-art lanthanum strontium cobalt ferrite (La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3–δ , LSCF) cathode is reported. The conformal MP catalyst-coated LSCF cathode shows a polarization resistance (R p ) of 0.048 Ω cm 2 at 650 °C, about one order of magnitude smaller than that of the bare LSCF. In an accelerated Cr-poisoning test, the degradation rate of the catalyst-coated LSCF electrode is 10 –3 Ω cm 2 h –1 (0.59% h –1 ) over 200 h, only one fifth of the degradation rate of the bare LSCF electrode at 750 °C. In addition, anode-supported single cells with the MP catalyst-coated LSCF cathode show a dramatically enhanced peak power density (1.4 W cm –2 vs 0.67 W cm –2 at 750 °C) and increased durability against Cr and H 2 O. Both experimental results and density functional theory-based calculations indicate that the BCFN phase improves the ORR activity while the BaCO 3 phase enhances the stability of the LSCF cathode.

solid oxide fuel cells↗
DOE OSTI2021

Wireless Optogenetic Modulation of Cortical Neurons Enabled by Radioluminescent Nanoparticles

While offering high precision control of neural circuits, optogenetics is hampered by the necessity to implant fiber-optic waveguides in order to deliver photons to genetically engineered light-gated neurons in the brain. Unlike laser light, X-rays freely pass biological barriers. In this work, we show that radioluminescent Gd 2 (WO 4 ) 3 :Eu nanoparticles, which absorb an external X-rays energy and then down-converter it into optical photons with wavelengths of ~610 nm, can be used for the transcranial stimulation of cortical neurons expressing red-shifted, ~590-630 nm, channelrhodopsin ReaChR, thereby promoting optogenetic neural control to the practical implementation of minimally-invasive wireless deep brain stimulation.

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

Promotion of oxygen reduction reaction on a double perovskite electrode by a water-induced surface modification

Highly efficient air electrodes are a key component of reversible fuel cells for energy storage and conversion; however, the development of efficient electrodes that are stable against water vapor remains a grand challenge. Here we report an air–electrode, composed of double perovskite material PrBa 0.8 Ca 0.2 Co 2 O 5+δ (PBCC) backbone coated with nanoparticles (NPs) of BaCoO 3-δ (BCO), that exhibits remarkable electrocatalytic activity for oxygen reduction reaction (ORR) while maintaining excellent tolerance to water vapor. When tested in a symmetrical cell exposed to wet air with 3 vol% H 2 O at 750 °C, the electrode shows an area specific resistance of ~0.03 Ω cm 2 in an extended period of time. The performance enhancement is attributed mainly to the electrocatalytic activity of the BCO NPs dispersed on the surface of the porous PBCC electrode. Moreover, in situ Raman spectroscopy is used to probe reaction intermediates (e.g., oxygen species) on electrode surfaces, as the electrochemical properties of the electrodes are characterized under the same conditions. The direct correlation between surface chemistry and electrochemical behavior of an electrode is vital to gaining insight into the mechanisms of the electrocatalytic processes in fuel cells and electrolysers.

25 ENERGY STORAGE↗
DOE OSTI2021

KPC-2 β-lactamase enables carbapenem antibiotic resistance through fast deacylation of the covalent intermediate

Serine active-site β-lactamases hydrolyze β-lactam antibiotics through the formation of a covalent acyl-enzyme intermediate followed by deacylation via an activated water molecule. Carbapenem antibiotics are poorly hydrolyzed by most β-lactamases owing to slow hydrolysis of the acyl-enzyme intermediate. However, the emergence of the KPC-2 carbapenemase has resulted in widespread resistance to these drugs, suggesting it operates more efficiently. Here, we investigated the unusual features of KPC-2 that enable this resistance. We show that KPC-2 has a 20,000-fold increased deacylation rate compared with the common TEM-1 β-lactamase. Furthermore, kinetic analysis of active site alanine mutants indicates that carbapenem hydrolysis is a concerted effort involving multiple residues. Substitution of Asn170 greatly decreases the deacylation rate, but this residue is conserved in both KPC-2 and non-carbapenemase β-lactamases, suggesting it promotes carbapenem hydrolysis only in the context of KPC-2. X-ray structure determination of the N170A enzyme in complex with hydrolyzed imipenem suggests Asn170 may prevent the inactivation of the deacylating water by the 6α-hydroxyethyl substituent of carbapenems. In addition, the Thr235 residue, which interacts with the C3 carboxylate of carbapenems, also contributes strongly to the deacylation reaction. In contrast, mutation of the Arg220 and Thr237 residues decreases the acylation rate and, paradoxically, improves binding affinity for carbapenems. Thus, the role of these residues may be ground state destabilization of the enzyme-substrate complex or, alternatively, to ensure proper alignment of the substrate with key catalytic residues to facilitate acylation. These findings suggest modifications of the carbapenem scaffold to avoid hydrolysis by KPC-2 β-lactamase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Increasing Capacity in Disordered Rocksalt Cathodes by Mg Doping

Using both computations and experiments, we demonstrate that the performance of Li-excess cation-disordered rocksalt cathodes can be improved by Mg substitution. Furthermore we find that Mg reduces the amount of Li in the compound that is strongly bound to F and thereby increases the capacity. This enables the use of fluorination as a tool to improve stability of the compounds without significant loss of capacity. Mg emerged as the most optimal substitution element from a systematic computational study aimed at identifying inactive doping elements with a strong enough bonding strength to fluorine to displace Li from the F environments. Our results also show that capacity can be traded for cycle life depending on whether Mg is substituted for Li or for the redox metal. This design strategy should be considered in fluorinated cathodes, which will facilitate the design of optimized disordered rocksalt oxyfluoride cathodes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗