Effect Of Local Electric Field Research Articles

Quantum Defect Sensitization via Phase-Changing Supercharged Antibody Fragments.

Quantum defects in single-walled carbon nanotubes promote exciton localization, which enables potential applications in biodevices and quantum light sources. However, the effects of local electric fields on the emissive energy states of quantum defects and how they can be controlled are unexplored. Here, we investigate quantum defect sensitization by engineering an intrinsically disordered protein to undergo a phase change at a quantum defect site. We designed a supercharged single-chain antibody fragment (scFv) to enable a full ligand-induced folding transition from an intrinsically disordered state to a compact folded state in the presence of a cytokine. The supercharged scFv was conjugated to a quantum defect to induce a substantial local electric change upon ligand binding. Employing the detection of a proinflammatory biomarker, interleukin-6, as a representative model system, supercharged scFv-coupled quantum defects exhibited robust fluorescence wavelength shifts concomitant with the protein folding transition. Quantum chemical simulations suggest that the quantum defects amplify the optical response to the localization of charges produced upon the antigen-induced folding of the proteins, which is difficult to achieve in unmodified nanotubes. These findings portend new approaches to modulate quantum defect emission for biomarker sensing and protein biophysics and to engineer proteins to modulate binding signal transduction.

Negative differential resistors from carbon-based cryogels incorporating graphene oxide into a ferroelectric polymer matrix

Electronic components with negative differential resistance (NDR) are essential in power electronics to build Gunn diodes, varactors, parametric amplifiers and switching circuits. However, their implementation through silicon-based electronics is costly and demands complex circuitry and components. Here, we introduce for the first time a class of hybrid carbon-based and organic aerogels, prepared at liquid nitrogen temperature (77 K) by a simple and scalable freeze-drying method. These cryogels exhibit NDR. In these cryogels, the carbonaceous phase is represented by d-glucose-graphene oxide nanocomposites while the organic phase is represented by polyvinylidene difluoride (PVDF), a ferroelectric polymer. NDR in our samples is assigned to the local electric field effects of PVDF on the charge carriers of more electrically conducting graphene oxide and d-glucose. Through an operando study via scanning near-field optical microscopy, we also show that low thermal expansion and low thermal conductivity are essential to prevent undesired effects in our devices through parasitic capacitance's discharge.

Enhanced photocatalytic performance of Mn-doped CeO2 nanoribbons for VOCs degradation: Investigating charge rearrangement and local electric field effects

In this study, we investigate Mn-doped CeO2 nanoribbons as photocatalysts to address the issue of performance enhancement in volatile organic compounds (VOCs) removal. Our primary focus centers on elucidating the interplay between charge rearrangement and local electric field (LEF) effects to uncover how these key factors collectively contribute to the improved photocatalytic performance. The successful doping of Mn atoms into the CeO2 lattice resulted in a strong dopant/matrix interaction effect. In situ XPS and density functional theory (DFT) calculations confirmed significant local charge rearrangement due to the dopant-induced local electric field, promoting charge carrier separation. The Mn dopant facilitated the generation of superoxide and hydroxide radicals. DFT simulations showed that Mn doping promoted VOCs adsorption on CeO2, favoring the subsequent oxidation process. The Mn-doped CeO2 nanoribbons achieved enhanced photodegradation performance of HCHO and CH3COCH3 compared to CeO2. This work aims to provide guidance and insights for the development of advanced photocatalysts.

Multi-branched AgAuPt nanoparticles for efficient electrocatalytic hydrogen evolution: Synergism of tip-enhanced electric field effect and local electric field effect

High-curvature multi-noble metallic heterostructures can effectively enhance the electrocatalytic hydrogen evolution performance by utilizing the synergism of tip-enhanced electric field effect and local electric field effect. Herein, we report a two-step synthesis strategy to obtain multi-branched high-curvature AgAuPt heterostructure, firstly amino acids-induced growth of Au branches on Ag nanocubes, and secondly L-AA reduction of H2PtCl6 to incorporate tiny Pt nanoparticles on Au branches. The D-CAgAuPt results in a low overpotential of 38 mV to deliver a cathodic current density of 10 mA cm−2, which is superior to commercial 20% Pt/C (46 mV). The strong electronic interactions between multi-noble metals intrinsically enhance the durability and stability of the catalysts. The intrinsic mechanism of promoting HER performance is investigated and revealed in-depth via the FDTD simulations and DFT calculations. In addition, D-CAgAuPt can also achieve efficient and stable hydrogen evolution in a proton exchange membrane electrolyzer, which has the potential for commercial practical application. This work designs a novel multi-branched high-curvature multi-noble metallic heterostructure, and fully provides insights into the generical and efficient enhancement of electrocatalytic HER performance of multi-noble metallic heterostructures.

Understanding the Mechanism of Butanol Formation from CO2 Reduction on Phosphorus Rich Copper Catalyst, CuP2, By Computer Simulations Based on Joint Density Functional Theory

Development of efficient, selective and cost-effective electrocatalysts is central to the efficient production of sustainable fuels and industrial feedstocks. While significant progress has been made in the hydrogen evolution reaction (HER) for water splitting, the direct synthesis of industrial fuels and feedstocks by the CO2 reduction reaction (CO2RR) still presents significant challenges related to the limited number of metals that maintain selectivity toward multi carbon products while operating at a low overpotential.Recent experimental work by Choi and co-workers1 has demonstrated the generation of 1-butanol from the reduction of CO2 on phosphorus-rich copper cathode. 1-butanol was produced at a record faradaic efficiency of approximately 4%. Interestingly, it was observed that carbon monoxide, CO, which is considered the preeminent intermediate for CO2 reduction reaction was not observed as an intermediate in this reaction. On previous copper based electrocatalysts, it has been shown that the C-C coupling through *CO dimerization is the rate limiting step that controls the selectivity toward multi carbon products.2-4 The absence of *CO as an intermediary for 1-butanol formation on CuP2 suggests the existence of a different mechanism is at a play.This presentation reports the results of computer simulations of this system based on Joint Density Functional Theory, JDFT,5 which combines a first-principles treatment of the electrocatalyst (CuP2) and adsorbed molecular fragments together with a realistic continuum model of other parts of the electrochemical environment. The simulations are used to explain the potential dependence and the mechanism of 1-butanol formation, and other experimentally observed products, on a CuP2 electrocatalyst. Traditional theoretical studies on electrocatalyst have used high vacuum DFT simulations, by using the computational hydrogen electrode, CHE, model.6 CHE presents a fundamental limitation on the description of electrochemical systems because it largely ignores solvation and local electric field effects, which are vital for the accurate description of electrochemical systems. Explicit inclusion of water into the theoretical simulation isn’t only limited by the many solvent molecules needed but also thermodynamic sampling of many configurations of those molecules to properly capture the structure and response of the liquid over realistic experimental time scales and lengths. In response to the above limitations, continuum solvation models are employed, in which the details of the molecular aqueous environment are replaced by a continuum description. In addition to solvation effects, the effect of the applied potential on the reaction is also investigated. The applied potential is represented by employing a grand canonical ensemble.Using the JDFT formalism, many configurations of molecular fragments on the CuP2 catalyst were considered and their optimal structures and energies were obtained. It is shown that the phosphorus atoms on CuP2 act as hydride binding sites. Thermodynamic and kinetic results show that the activation of physically adsorbed CO2 by chemically adsorbed H favors the formation of formate (HCOO) which is adsorbed on Cu sites through its oxygens, over the formation of carboxyl (*COOH) intermediate. The unfavorable carboxyl intermediate likely explains why *CO is not observed as an intermediate in experimental work.1 The formation of multi-carbon products is controlled by the C-C coupling step. We show that the coupling step occurs through the aldol condensation first between two formaldehyde then through two acetaldehyde adsorbates. These findings not only explain the experimentally observed products but also illustrate an alternative mechanism toward multi-carbon formation on electrocatalysts that does not involve CO-CO coupling step.Reference M. Choi, S. Bong, J. Won Kim, J. Lee. ACS. Energy. Lett. 2021 , 6 , 2090-2095J. Montoya, C. Shi, K. Chan, J. K. Norskov. J. Phys. Chem. Lett. 2015, 6, 2032-2037J. Montoya, A. Peterson, J. K. Norskov. Chem. Cat. Chem. 2013, 5,737-742H. Xiao, T. Cheng, W. A. Goddard, R. Sundararaman. J. Am. Chem. Soc. 2016, 138, 483-486R. Sundararaman, K. Letchworth-Weaver, K. A. Schwarz, D. Gunceler, Y. Ozhabes, and T. A. Aria, SoftwareX, 2017, 6, 278-284; K. Schwarz and R. Sundararaman, Surface Science Reports, 2020, 75, 100492A. Peterson, F. Abild-Pedersen, F. Studt, J. Rossmeisl, J. K. Norskov. Energy Environ. Sci. 2010, 3, 1311-1315 Acknowledgement:This work was supported by the Wake Forest Chemistry Department. Computations were performed on the Wake Forest University DEAC Cluster, a centrally managed resource with support provided in part by the University.

Tuning the Interface of Co1-xS/Co(OH)F by Atomic Replacement Strategy toward High-Performance Electrocatalytic Oxygen Evolution.

The construction of heterostructures is one of the most promising strategies for engineering interfaces of catalysts to perform high-efficiency oxygen evolution reaction (OER). However, accurately tuning heterostructures' interface during operation remains a challenge. Herein, we fabricated the needled-like heterostructure Co1-xS/Co(OH)F supported on flexible carbon fiber cloth via an atomic substitution strategy, in which sulfur atoms are simultaneously grafted into F vacancies after the partial removal of F atoms from Co(OH)F during the electrodeposition, thus achieving the growth of cobalt sulfide on the interface of Co(OH)F. This electrocatalyst with such design exhibits the following advantages: (1) The lattice distortion caused by atomic substitution leads to the increase of active sites; (2) Co1-xS constructed on the surface of Co(OH)F by the atomic replacement strategy optimizes the adsorption (OH-) and desorption (O2) energy in the OER process; (3) the needle-like structure possesses the tip-enhanced local electric field effect. As a result, the Co1-xS/Co(OH)F/CC catalyst exhibits very high OER catalytic performance with an overpotential of 269 mV at a current density of 10 mA cm-2 and a Tafel slope of 71 mV dec-1. The asymmetric electrode shows superior catalytic activity and stability in overall water splitting. The catalytic mechanism of these highly efficient Co1-xS/Co(OH)F/CC catalysts was investigated via DFT theoretical calculations and ex situ characterizations. This atomic substitution strategy displays universality for other transition metal sulfides (metal = Ni, Mn, Cu).

Chloride-Mediated Alkene Activation Drives Enantioselective Thiourea and Hydrogen Chloride Co-Catalyzed Prins Cyclizations.

The mechanism of chiral hydrogen-bond donor (HBD) and hydrogen chloride (HCl) co-catalyzed Prins cyclizations was analyzed through a combination of experimental and computational methods and revealed to involve an unexpected and previously unrecognized mode of alkene activation. Kinetic and spectroscopic studies support the participation of a catalytically active HCl·HBD complex that displays reduced Brønsted acidity relative to HCl alone. Nevertheless, rate acceleration relative to the HCl-catalyzed background reaction as well as high levels of enantioselectivity are achieved. This inverse Brønsted correlation is ascribed to chloride-mediated substrate activation in the rate-limiting and enantiodetermining cyclization transition state. Density functional theory (DFT) calculations, distortion-interaction analysis, and quasiclassical dynamics simulations support a stepwise mechanism in which rate acceleration and enantioselectivity are achieved through the precise positioning of the chloride anion within the active site of the chiral thiourea to enhance the nucleophilicity of the alkene and provide transition-state stabilization through local electric field effects. This mode of selective catalysis through anion positioning likely has general implications for the design of enantioselective Brønsted acid-catalyzed reactions involving π-nucleophiles.

An ultrasensitive bacteria biosensor using “multilayer cake” silver microelectrode based on local high electric field effect

A signal response mechanism of local high electric field effects was designed to detect bacteria using a chemically modified “multilayer cake” micro-nanostructured pillar electrode. Since the silver electrode has a strong specific electrochemical signal response to chloride ions, we choose silver as the electrode material. The microelectrode was prepared by a one-step localized electrochemical deposition method without the use of mold. Then the electrode was successively functionalized with chitosan, catechol, and aptamer. Many nano- and micro-scale protrusion tips on the electrode surface generated a local high electric field and drove the leakage of intracellular chloride ions when bacteria were captured by APT; thus, a reduced signal of the silver electrode related to chloride ions was recorded. A pseudocapacitor structure composed of chitosan, catechol, Ru3+, and Fc was constructed on an electrode surface to further amplify the signal. The electrochemical sensor based on this electrode showed excellent performance for template bacteria Staphylococcus aureus detection in terms of the detection limit (1 CFU mL−1), linear response range (1–105 CFU mL−1), and specificity. This work provides another way to design an electrochemical biosensor using the nanoeffect of the electrode rather than the conventional current response based on the electrical properties of the bacterial surface.

Impact of enhanced electric field on light-induced evaporation process of plasmonic nanofluid

Recently, some studies have shown that the vaporization of plasmonic nanofluids (PNFs) is observed to be more intensive than that of pure water during the light-induced heating process, but the mechanism remains controversial. In this work, we conduct several comparative experiments and molecular dynamics (MD) simulations to investigate the evaporation process of PNFs under the illumination of different monochromatic incident lights, especially focusing on the plasma-mediated evaporation mechanism. Based on the experimental results of silver, gold, and graphite nanofluids, it is found that the evaporation process of PNFs can be heavily promoted under the combined effect of the enhanced electric field induced by the localized surface plasmon resonance (LSPR) and the thermal diffusion. Combined with the electromagnetic theory, a modified MD simulation is developed to analyze the effect of the induced electric field on the evaporation process of PNFs. The results indicate that nanoparticles with the LSPR effect are not only ‘heat sources’ which transfer the thermal energy to the surrounding media, but also can produce the enhanced electric field to directly impact the motion of water molecules. The effect of localized electric field on the evaporation of PNFs cannot be neglected, especially during the initial evaporation period when the particle temperature is relatively low. The results also reveal that the light-induced evaporation process of PNFs is quite different from the conventional thermo-mediated evaporation process in carbon-based nanofluids. Besides, some necessary conditions for exciting the plasma-mediated evaporation are also discussed. This work can offer some new insights for a comprehensive understanding of the evaporation process of PNFs, which is of fundamental interest to many emerging applications.

Localized surface plasmon resonance-enhanced solar-blind Al0.4Ga0.6N MSM photodetectors exhibiting high-temperature robustness

The appealing properties of tunable direct wide bandgap, high-temperature robustness and chemical hardness, make Al x Ga1−x N a promising candidate for fabricating robust solar-blind photodetectors (PDs). In this work, we have utilized the optical phenomenon of localized surface plasmon resonance (LSPR) in metal nanoparticles (NPs) to significantly enhance the performance of solar-blind Al0.4Ga0.6N metal–semiconductor–metal PDs that exhibit high-temperature robustness. We demonstrate that the presence of palladium (Pd) NPs leads to a remarkable enhancement by nearly 600, 300, and 462%, respectively, in the photo-to-dark current ratio (PDCR), responsivity, and specific detectivity of the Al0.4Ga0.6N PD at the wavelength of 280 nm. Using the optical power density of only 32 μW cm−2 at −10 V, maximum values of ∼3 × 103, 2.7 AW−1, and 2.4 × 1013 Jones are found for the PDCR, responsivity and specific detectivity, respectively. The experimental observations are supported by finite difference time domain simulations, which clearly indicate the presence of LSPR in Pd NPs decorated on the surface of Al0.4Ga0.6N. The mechanism behind the enhancement is investigated in detail, and is ascribed to the LSPR induced effects, namely, improved optical absorption, enhanced local electric field and LSPR sensitization effect. Moreover, the PD exhibits a stable operation up to 400 K, thereby exhibiting the high-temperature robustness desirable for commercial applications.

The local electric field effect of onion-like carbon nanoparticles for improved laser desorption/ionization efficiency of saccharides

It is still a challenge to improve ionization efficiency of saccharides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Herein, the highly curved onion-like carbon nanoparticles (OCS) were synthesized from the low-price candle raw via a facile strategy. The unique nanostructure of OCS showed large surface area with plentiful mesoporous architecture, highly curved sp2 carbon with regulating electronic effect, and good hydrophilicity, which could be beneficial to facilitate the desorption and ionization efficiency in MS process. The prepared OCS material as MALDI matrix exhibited the superior performance for the detection of xylose, glucose, maltose monohydrate, and raffinose pentahydrate in positive-ion mode with low background noise, enhanced ion intensities, uniform distribution, excellent reproducibility, good salt-tolerance, and high sensitivity compared to control candle soot (CS) and traditional α-cyano-4-hydroxycinnamic acid (CHCA) matrices. This highly effective LDI of OCS matrix was attributed to its enhancing local electric field effect, strong UV absorption ability, and high photo-thermal conversion performance. Furthermore, the OCS-assisted LDI MS approach was employed to quantitatively detect glucose in rat serum. This LDI MS platform may have valuable for the analysis of metabolites in clinical research.

Local Charge Distributions, Electric Dipole Moments, and Local Electric Fields Influence Reactivity Patterns and Guide Regioselectivities in α-Ketoglutarate-Dependent Non-heme Iron Dioxygenases.

Non-heme iron dioxygenases catalyze vital processes for human health related to the biosynthesis of essential products and the biodegradation of toxic metabolites. Often the natural product biosyntheses by these non-heme iron dioxygenases is highly regio- and chemoselective, which are commonly assigned to tight substrate-binding and positioning. However, recent high-level computational modeling has shown that substrate-binding and positioning is only part of the story and long-range electrostatic interactions can play a major additional role.In this Account, we review and summarize computational viewpoints on the high regio- and chemoselectivity of α-ketoglutarate-dependent non-heme iron dioxygenases and how external perturbations affect the catalysis. In particular, studies from our groups have shown that often a regioselectivity in enzymes can be accomplished by stabilization of the rate-determining transition state for the reaction through external charges, electric dipole moments, or local electric field effects. Furthermore, bond dissociation energies in molecules are shown to be influenced by an electric field effect, and through targeting a specific bond in an electric field, this can lead to an unusually specific reaction. For instance, in the carbon-induced starvation protein, we studied two substrate-bound conformations and showed that regardless of what C-H bond of the substrate is closest to the iron(IV)-oxo oxidant, the lowest hydrogen atom abstraction barrier is always for the pro-S C2-H abstraction due to an induced dipole moment of the protein that weakens this bond. In another example of the hygromycin biosynthesis enzyme, an oxidative ring-closure reaction in the substrate forms an ortho-δ-ester ring. Calculations on this enzyme show that the selectivity is guided by a protonated lysine residue in the active site that, through its positive charge, triggers a low energy hydrogen atom abstraction barrier. A final set of examples in this Account discuss the viomycin biosynthesis enzyme and the 2-(trimethylammonio)ethylphosphonate dioxygenase (TmpA) enzyme. Both of these enzymes are shown to possess a significant local dipole moment and local electric field effect due to charged residues surrounding the substrate and oxidant binding pockets. The protein dipole moment and local electric field strength changes the C-H bond strengths of the substrate as compared to the gas-phase triggers the regioselectivity of substrate activation. In particular, we show that in the gas phase and in a protein environment C-H bond strengths are different due to local electric dipole moments and electric field strengths. These examples show that enzymes have an intricately designed structure that enables a chemical reaction under ambient conditions through the positioning of positively and negatively charged residues that influence and enhance reaction mechanisms. These computational insights create huge possibilities in bioengineering to apply local electric field and dipole moments in proteins to achieve an unusual selectivity and specificity and trigger a fit-for-purpose biocatalyst for unique biotransformations.

Local electric field effect of montmorillonite in solid polymer electrolytes for lithium metal batteries

Solid polymer electrolytes (SPEs) with in-built inorganic fillers are very promising for building safe solid-state batteries, owing to their excellent flexibility, prominent interfacial wettability and low costs. However, the morphology and surface state of inorganic fillers greatly affect ionic conductivity of SPEs. Here, we report that ultraviolet (UV) initiates in situ cross-linking of poly(ethylene glycol) methyl ether acrylate (MPEGA), poly(ethylene glycol) diacrylate (PEGDA) and montmorillonite (MMT) between cathodes and anodes of cell, to produce a solid composite electrolyte (CMP/MMT) that is composed of a robust interpenetrating polymer network matrix and layered MMT nanosheets. Surprisingly, the CMP/MMT delivers a high room-temperature ionic conductivity (~1.06 mS cm−1), large lithium-ions transference number (tLi+ = 0.79). The large ionic conductivity enhancement is ascribed to the local electric field effect of montmorillonite (MMT), which accelerates the lithium-ions fast transport in the interlayer of the MMT nanosheets. In addition, the density functional theory (DFT) is conducted to demonstrate the mechanism of improving ionic conductivity. As a result, a solid-state battery with CMP/MMT demonstrates a high capacity of ~140 mAh g−1 and excellent capacity retention of >98% at 0.3 C after 400 cycling.

Insights into enhancement of photocatalytic properties of g-C3N4 by local electric field induced by polarization of MgO(111)

Photocatalysis has attracted worldwide attention in the fields of energy storage and environmental remediation. However, the solar-to-energy conversion efficiency is still low due to fast charge carrier recombination in the bulk phase of conventional photocatalysts. Herein, a series of photocatalysts including g-C3N4 (GCN), non-polar MgO(110)/GCN composite, MgO(110)+GCN mixture, polar MgO(111)/GCN composite, and MgO(111)+GCN mixture are prepared and their photocatalytic activities are investigated systematically. The polar and non-polar MgO improve the photocatalytic properties of GCN in the following order: MgO(111)+GCN>MgO(110)/GCN>MgO(111)/GCN>MgO(110)+GCN>GCN. Benefiting from charge carrier separation rendered by the local electric field (LEF) induced by MgO(111) polarization, MgO(111) improves the performance of GCN significantly when it is mixed with GCN. However, the enhancement effects are reduced when it is combined with or integrated into GCN as in the MgO(111)/GCN composite, where the traditional heterojunction effect constitutes the main enhancement mechanism. Our study reveals that the photocatalytic enhancement by the LEF effect is superior to that by the traditional heterojunction effect based on polar supporting materials. Our results offer insights into the enhancement mechanism of photocatalysts with polar supporting materials and reveal a simple strategy to optimize photocatalytic processes to exploit solar energy efficiently.

Frequency Shift Surface-Enhanced Raman Spectroscopy Sensing: An Ultrasensitive Multiplex Assay for Biomarkers in Human Health.

The sensitive and selective detection of biomarkers for human health remains one of the grand challenges of the analytical sciences. Compared to established methods (colorimetric, (chemi) luminescent), surface-enhanced Raman spectroscopy (SERS) is an emerging alternative with enormous potential for ultrasensitive biological detection. Indeed even attomolar (10-18 M) detection limits are possible for SERS due to an orders-of-magnitude boosting of Raman signals at the surface of metallic nanostructures by surface plasmons. However, challenges remain for SERS assays of large biomolecules, as the largest enhancements require the biomarker to enter a "hot spot" nanogap between metal nanostructures. The frequency-shift SERS method has gained popularity in recent years as an alternative assay that overcomes this drawback. It measures frequency shifts in intense SERS peaks of a Raman reporter during binding events on biomolecules (protein coupling, DNA hybridization, etc.) driven by mechanical transduction, charge transfer, or local electric field effects. As such, it retains the excellent multiplexing capability of SERS, with multiple analytes being identifiable by a spectral fingerprint in a single read-out. Meanwhile, like refractive index surface plasmon resonance methods, frequency-shift SERS measures the shift of an intense signal rather than resolving a peak above noise, easing spectroscopic resolution requirements. SERS frequency-shift assays have proved particularly suitable for sensing large, highly charged biomolecules that alter hydrogen-bonding networks upon specific binding. Herein we discuss the frequency-shift SERS method and promising applications in (multiplex) biomarker sensing as well as extensions to ion and gas sensing and much more.

Effect of local electric field on trans to cis photo-isomerization of azobenzene containing polymer

We report the effect of local electric field on the rate of photo-isomerization of azobenzene containing poly ethylene glycol-itaconate based side chain liquid crystalline polymer (PEGIA) in the ultra-thin film at air–water interface. The local electric fields were realised by adding polar polyvinylidene difluoride (PVDF) molecules in the PEGIA thin film. The ultra-thin film of PEGIA mixed with PVDF in different weight percentages were formed at air–water interface and are characterized using surface manometry technique. The rate constant of trans-cis photo-isomerization (k1) of azobenzene moieties in the presence of different amounts of PVDF were obtained from the surface pressure measurements. We find that the k1 exponentially increases with the percentage composition of PVDF which can be attributed to the effect of electric field due to the dipole moment of the PVDF molecules. The change in the activation energy of the photo-isomerization as a function of percentage composition of PVDF is calculated.

Selective CO2 Electrochemical Reduction Enabled by a Tricomponent Copolymer Modifier on a Copper Surface.

Electrochemical CO2 reduction over Cu could provide value-added multicarbon hydrocarbons and alcohols. Despite recent breakthroughs, it remains a significant challenge to design a catalytic system with high product selectivity. Here we demonstrate that a high selectivity of ethylene (55%) and C2+ products (77%) could be achieved by a highly modular tricomponent copolymer modified Cu electrode, rivaling the best performance using other modified polycrystalline Cu foil catalysts. Such a copolymer can be conveniently prepared by a ring-opening metathesis polymerization, thereby offering a new degree of freedom for tuning the selectivity. Control experiments indicate all three components are essential for the selectivity enhancement. A surface characterization showed that the incorporation of a phenylpyridinium component increased the film robustness against delamination. It was also shown that its superior performance is not due to a morphology change of the Cu underneath. Molecular dynamics (MD) simulations indicate that a combination of increased local CO2 concentration, increased porosity for gas diffusion, and the local electric field effect together contribute to the increased ethylene and C2+ product selectivity.

Tip-Enhanced Electric Field: A New Mechanism Promoting Mass Transfer in Oxygen Evolution Reactions.

The slow kinetics of oxygen evolution reaction (OER) causes high power consumption for electrochemical water splitting. Various strategies have been attempted to accelerate the OER rate, but there are few studies on regulating the transport of reactants especially under large current densities when the mass transfer factor dominates the evolution reactions. Herein, Nix Fe1- x alloy nanocones arrays (with ≈2 nm surface NiO/NiFe(OH)2 layer) are adopted to boost the transport of reactants. Finite element analysis suggests that the high-curvature tips can enhance the local electric field, which induces an order of magnitude higher concentration of hydroxide ions (OH- ) at the active sites and promotes intrinsic OER activity by 67% at 1.5 V. Experimental results show that a fabricated NiFe nanocone array electrode, with optimized alloy composition, has a small overpotential of 190 mV at 10 mA cm-2 and 255 mV at 500 mA cm-2 . When calibrated by electrochemical surface area, the nanocones electrode outperforms the state-of-the-art OER electrocatalysts. The positive effect of the tip-enhanced local electric field in promoting mass transfer is also confirmed by comparing samples with different tip curvature radii. It is suggested that this local field enhanced OER kinetics is a generic effect to other OER catalysts.

Superconductivity-induced transverse plasma mode and phonon anomaly in the c -axis response of the bilayer compound RbCa2Fe4As4F2

With infrared spectroscopy we studied the out-of-plane ($c$-axis) response of the iron arsenide superconductor ACa$_2$Fe$_4$As$_4$F$_2$ (A = Rb,Cs) which has a bilayer structure similar to the high $T_c$ cuprates YBa$_2$Cu$_3$O$_7$ (YBCO) and Bi$_2$Sr$_2$CaCu$_2$O$_8$ (Bi2212). In analogy to the cuprates, we observe a superconductivity-induced transverse plasma mode (tPM) and a phonon anomaly that are both signatures of local electric field effects that arise from a large difference between the local conductivities in the intra- and inter-bilayer regions. Using a multilayer model developed for the cuprates, we obtain a good description of the $c$-axis response and derive the local conductivities at $T \simeq T_c$ of $\sigma_1^{\mathrm{bl}}(\omega \rightarrow 0) \simeq$ 1\,000 $\Omega^{-1}\mathrm{cm}^{-1}$ and $\sigma_1^{\mathrm{int}}(\omega \rightarrow 0) \simeq$ 15 $\Omega^{-1}\mathrm{cm}^{-1}$, respectively, that are similar to the ones previously found in underdoped YBCO. Different from the cuprates, we find no evidence of a normal state pseudogap in terms of a partial suppression of the low-energy electronic states that sets in already well above $T_c$. There is also no clear sign of an onset of precursor superconducting pairing correlations well above $T_c \simeq$ 30~K. This highlights that the pseudogap and the precursor superconducting pairing well above $T_c$ are unique features of the cuprates with their strong electronic correlations and, for example, not just the result of a strongly anisotropic electronic response due to the layered crystal structure.

The enhanced photocatalytic activity of Ag-OVs-(0 0 1) BiOCl by separating secondary excitons under double SPR effects

The Ag-OVs-(0 0 1) BiOCl photocatalysts were synthesized by photodeposition method. The strong singlet oxygen signal meant that BiOCl only produce very few free electrons and not enough to reduce Ag+ to Ag. Inevitably, the “hot electrons” of oxygen vacancies reduced Ag+ and Ag occupied oxygen vacancies of BiOCl. Under light, high-energy electrons of Ag were propagated to BiOCl by propagating surface plasmon resonance (TSPR), and the high-energy electrons scrambled for the holes of primary excitons in BiOCl to form secondary excitons. The electrons in the primary excitons were released, while the secondary excitons were captured by oxygen vacancies and the holes of secondary excitons were released. The electrons released from primary excitons and the holes released from secondary excitons were accelerated to separate under the local electric field (LSPR) effect of Ag, and lots of superoxide radicals and holes participated in the catalytic reaction. The photocatalytic activity of Ag-OVs-(0 0 1) BiOCl was improved under the polarization charges, TSPR and LSPR effects of Ag, and the degradation rate of RhB by Ag-OVs-(0 0 1) BiOCl was 2.64 times that of BiOCl under the simulated sunlight.