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Chen, Zhu

Publications and source records attributed to Chen, Zhu.

10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Operando probing dynamic migration of copper carbonyl during electrocatalytic CO2 reduction

Single crystals and shape-controlled nanocrystals are well known to exhibit facet-dependent catalytic properties. However, few studies have investigated how those nanocrystals evolve and (de)activate during reactions, calling for the development of nanoscale time-resolved operando methods. In this context, we have designed Cu nanocubes as a model system to elucidate the underlying driving force of dynamic nanocatalyst reconstruction during the CO2 reduction reaction (CO2RR). Operando electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM) and synchrotron-based X-ray spectroscopy reveal the size- and potential-dependent complete transformation from (100)-oriented Cu@Cu2O nanocubes to polycrystalline metallic Cu nanograins under CO2RR conditions. In addition, machine learning-assisted operando four-dimensional STEM reveals that large Cu nanograins derived from nanocubes form mainly crystalline domains, while their smaller counterparts are more amorphous due to faster evolution kinetics. In situ Raman spectroscopy and density functional theory calculations suggest that CO drives the ejection of single Cu atoms, resulting in few-nanometre Cu clusters and the surface migration of highly mobile copper carbonyl (Cu–CO) species. Combined, these multimodal operando methods and theoretical approaches pave the way for understanding the complex structural evolution of energy-related nanocatalysts under electrochemical conditions.

Yang, Yao↗
DOE OSTI2024

Progress and roadmap for electro-privileged transformations of bio-derived molecules

Biomass incorporates carbon captured from the atmosphere and can serve as a renewable feedstock for producing valuable chemicals and fuels. Here we look at how electrochemical approaches can impact biomass valorization, focusing on identifying chemical transformations that leverage renewable electricity and feedstocks to produce valorized products via electro-privileged transformations. First, we recommend that the field should explore widening the spectrum of platform chemicals derived from bio-feedstocks, thus offering pathways to molecules that have historically been derived from petroleum. Second, we identify opportunities in electrocatalytic production of energy-dense fuels from biomass that utilize water as the hydrogen source and renewable electricity as the driving force. Finally, we look at the potential in electrochemical depolymerization to preserve key functional groups in raw feedstocks that would otherwise be lost during harsh pre-treatments in traditional depolymerization routes. Finally, on the basis of these priorities, we suggest a roadmap for the integration of biomass and electrochemistry and offer milestones required to tap further into the potential of electrochemical biomass valorization.

electrocatalysis↗
DOE OSTI2021

Increasing Iridium Oxide Activity for the Oxygen Evolution Reaction with Hafnium Modification

Synthesis and implementation of highly active, stable, and affordable electrocatalysts for the oxygen evolution reaction (OER) is a major challenge in developing energy efficient and economically viable energy conversion devices such as electrolyzers, rechargeable metal-air batteries, and regenerative fuel cells. The current benchmark electrocatalyst for OER is based on iridium oxide (IrO x ) due to its superior performance and excellent stability. However, large scale applications using IrO x are impractical due to its low abundance and high cost. In this work, we report a highly active hafnium-modified iridium oxide (IrHf x O y ) electrocatalyst for OER. The IrHf x O y electrocatalyst demonstrated ten times higher activity in alkaline conditions (pH = 11) and four times higher activity in acid conditions (pH = 1) than a IrO x electrocatalyst. The highest intrinsic mass activity of the IrHf x O y catalyst in acid conditions was calculated as 6950 A gIrO x -1 at an overpotential (η) of 0.3 V. Combined studies utilizing operando surface enhanced Raman spectroscopy (SERS) and DFT calculations revealed that the active sites for OER are the Ir-O species for both IrO x and IrHf x O y catalysts. The presence of Hf sites leads to more negative charge states on nearby O sites, and shortening the bond lengths of Ir-O, and lowering free energies for OER intermediates to accelerate the OER process.

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

Combustion studies of n-butyl acetate synthesized by a new biological process and comparisons with neat n-butyl acetate

Blending petroleum fuels with biofuels is a common approach for stemming the depletion of crude oil while also mitigating the impact of their combustion on the environment. It has recently been considered that n-butyl acetate (BA, C6H12O2, boiling point of 399K) could be a viable biofuel additive to diesel fuel. This paper reports the combustion dynamics of BA droplets in the absence of external convection. Two grades of BA were examined: one synthesized by a new process that uses a solventogenic Clostridium strain through an extractive fermentation process using n-hexadecane as the extractant (SBA); the other commercially available as a high-purity (99.9%) 'neat' BA grade produced by Fischer esterification (NBA). The mass concentration of by-products from the synthesis process amounted to approximately 6% of the total composition and included n-butanol, n-hexadecane, iso-propyl alcohol and ethyl acetate. The platform used to study the combustion of commercial and synthesized BA was an isolated droplet burning with spherical symmetry. Initial droplet diameters were fixed at 0.6 mm. Experiments were carried out in a drop tower to promote one-dimensional transport dynamics, in the standard atmosphere, and with ignition accomplished by spark discharge. Differences in droplet burning rates and flame structures were undetectable between NBA and SBA, despite the differences in burning among the SBA components individually. The results presented show that the new synthesis process for butyl acetate yields a sustainable alternative to conventional methodologies with burning characteristics that are identical to NBA in stagnant gas transport fields.

Wang, Yujie↗
DOE OSTI2021

Single-Molecule Charge Transport through Positively Charged Electrostatic Anchors

The charge transport in single-molecule junctions depends critically on the chemical identity of the anchor groups that are used to connect the molecular wires to the electrodes. In this research, we report a new anchoring strategy — called the electrostatic anchor here — formed through the efficient Coulombic interaction between the gold electrodes and the positively charged pyridinium terminal groups. Our results show that these pyridinium groups serve as efficient electrostatic anchors forming robust gold–molecule–gold junctions. Here, we have also observed binary switching in dicationic viologen molecular junctions, demonstrating an electron injection-induced redox switching in single-molecule junctions. We attribute the difference in low- and high conductance states to a dicationic ground state and a radical cationic metastable state, respectively. Overall, this anchoring strategy and redox switching mechanism could constitute the basis for a new class of redox-activated single-molecule switches.

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

Nano on micro: tuning microbial metabolisms by nano-based artificial mediators to enhance and expand production of biochemicals

Advances in synthetic biology and metabolic engineering across the past few decades have enabled the successful production of many novel chemicals. However, bioproduction of such chemicals is often limited by low yield and titer due to disrupted metabolic homeostasis. Finely tuning cellular metabolism to restore robust metabolic functions entails various genetic modifications, which is often not practical. Alternatively, artificial mediators capable of tailoring microbial metabolisms open a new avenue for restoring physiological functions. In this context, nanoparticle-based artificial mediators have been pursued to tune cellular metabolisms. They can not only enhance production of molecules from endogenous metabolism, but also expand bioproducts spectrum. Here, we reviewed recent advances toward the employment of nano-based artificial mediators for the tuning of cellular metabolism, with a focus on their positive effects on electron transfer and pathway flux. Perspectives for potential applications of artificial mediators for mediating microbial metabolisms in the future were also provided.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Lignin extraction and upgrading using deep eutectic solvents

Deep eutectic solvents (DESs) are a class of green solvents exhibiting low vapor pressure, high thermal stability,low toxicity, and biodegradability. These features make them attractive solvents for lignocellulosic biomassprocessing, especially for lignin valorization. DESs not only solubilize lignin from lignocellulose biomass, butalso confer extracted lignin with properties favorable to its further upgrading. This review summarizes recentadvances in biomass fractionation using DESs for lignin extraction. It also covers lignin upgrading in DESs interms of depolymerization and functionalization. The challenges of tailoring lignin properties by DESs for differentvalorization routes are also discussed.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Structural and stellar-population properties versus bulge types in Sloan Digital Sky Survey central galaxies

ABSTRACT This paper studies pseudo-bulges (P-bulges) and classical bulges (C-bulges) in Sloan Digital Sky Survey (SDSS) central galaxies using the new bulge indicator ΔΣ1, which measures relative central stellar-mass surface density within 1 kpc. We compare ΔΣ1 to the established bulge-type indicator Δ〈μe〉 from Gadotti (2009) and show that classifying by ΔΣ1 agrees well with Δ〈μe〉. ΔΣ1 requires no bulge–disc decomposition and can be measured on SDSS images out to z = 0.07. Bulge types using it are mapped on to 20 different structural and stellar-population properties for 12 000 SDSS central galaxies with masses 10.0 < log M*/M⊙ < 10.4. New trends emerge from this large sample. Structural parameters show fairly linear log–log relations versus ΔΣ1 and Δ〈μe〉 with only moderate scatter, while stellar-population parameters show a highly non-linear ‘elbow’ in which specific star formation rate remains roughly flat with increasing central density and then falls rapidly at the elbow, where galaxies begin to quench. P-bulges occupy the low-density end of the horizontal arm of the elbow and are universally star forming, while C-bulges occupy the elbow and the vertical branch and exhibit a wide range of star formation rates at a fixed density. The non-linear relation between central density and star formation rate has been seen before, but this mapping on to bulge class is new. The wide range of star formation rates in C-bulges helps to explain why bulge classifications using different parameters have sometimes disagreed in the past. The elbow-shaped relation between density and stellar indices suggests that central structure and stellar populations evolve at different rates as galaxies begin to quench.

Luo, Yifei↗