Tip-like Fe-N4 Sites Induced Surface Microenvironments Regulation Boosts the Oxygen Reduction Reaction

Single atom catalysts with defined local structures and favorable surface microenvironments are significant for overcoming slow kinetics and accelerating O2 electroreduction. Here, enriched tip-like FeN4 sites (T-Fe SAC) on spherical carbon surfaces were developed to investigate the change in surface microenvironments and catalysis behavior. Finite element method (FEM) simulations, together with experiments, indicate the strong local electric field of the tip-like FeN4 and the more denser interfacial water layer, thereby enhancing the kinetics of the proton-coupled electron transfer process. In situ spectroelectrochemical studies and the density functional theory (DFT) calculation results indicate the pathway transition on the tip-like FeN4 sites, promoting the dissociation of O-O bond via side-on adsorption model. The adsorbed OH* can be facilely released on the curved surface and accelerate the oxygen reduction reaction (ORR) kinetics. The obtained T-Fe SAC nanoreactor exhibits excellent ORR activities (E1/2 =0.91 V vs. RHE) and remarkable stability, exceeding those of flat FeN4 and Pt/C. This work clarified the in-depth insights into the origin of catalytic activity of tip-like FeN4 sites and held great promise in industrial catalysis, electrochemical energy storage, and many other fields.

Ferroelectric BaTiO3 Regulating the Local Electric Field for Interfacial Stability in Solid-State Lithium Metal Batteries

Solid-state Li metal batteries (SSLMBs) are widely investigated since they possess promising energy density and high safety. However, the poor interfacial compatibility between the electrolyte and electrodes limits their promising development. Herein, a robust composite electrolyte (poly(vinyl ethylene carbonate) electrolyte with 3 wt % of BaTiO3, PVEC-3BTO) with excellent interfacial performance is rationally designed by incorporating ferroelectric BaTiO3 (BTO) nanoparticles into the poly(vinyl ethylene carbonate) (PVEC) electrolyte matrix. Benefiting from the high dielectric constant and ferroelectric properties of BTO, the interfacial compatibility between electrolytes and electrodes was significantly improved. The enhanced Li+ transference number (0.64) of solid electrolyte and in situ generated BaF2 inorganic interphase contribute to the enhanced cycling stability of PVEC-3BTO based Li//Li symmetrical batteries. Furthermore, the antioxidation ability of PVEC-3BTO has also been enhanced by modulating the local electric field for good pairing with high-voltage LiCoO2 material. Therefore, in this work, the mechanism of BTO for improving interfacial compatibility is revealed, and also useful methods for addressing the interface issues of SSLMBs have been provided.

Field-Assisted Regulation Induced by Cobalt-Doped ZnO for Dendrite-Free Lithium Metal Anodes

Lithium metal batteries are deemed as an optimal candidate for the next generation of durable energy storage devices. However, the growth of lithium dendrite and significant volume expansion pose as obstacles that impede the application of lithium metal batteries. In this work, a functional copper current collector was designed by coating it with Co-doped ZnO (Co/ZnO) to enhance the lithiophilicity through local electric fields and built-in magnetic fields induced by the ferromagnetic material. The incorporation of Co not only induces a local electric field and thus accelerating electron transfer, but also imparts the ferromagnetic behavior to ZnO, resulting in an internal magnetic field to regulate the dynamic trajectory. Profiting from the above advantages, the symmetric cells have excellent cycle stability in 1 mA cm-2 and 1 mAh cm-2 , maintaining ultra-low voltage for over 2000 h. This study provides a realizable pathway for next-generation current collector of copper modification.

Nanotip-Induced Electric Field for Hydrogen Catalysis

Local electric field induced by the lightning-rod effect attracts great attention for regulating the local microenvironment and electronic properties of active sites. Nevertheless, local electric-field-assisted applications are mainly limited to metals with strong surface plasmonic resonance properties (e.g., Au, Ag, and Cu). Herein, we fabricate RuCu snow-like nanosheets (SNSs) with high-curvature nanotips for enhancing the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER). Theoretical simulations show that RuCu SNSs can induce a strong local electric field around the sharp nanotips, which favors the accumulation of OH- for HOR and H+ for HER. Cu incorporation can modulate the binding strength of OH* and H*, leading to significantly enhanced HOR and HER performance. Impressively, the mass activity of RuCu SNSs for alkaline HOR is 31.3 times higher than that of RuCu nanocrystals without sharp tips. Besides, the required overpotential for reaching 10 mA cm-2 during HER over RuCu SNSs is 14.0 mV.

Carbon-Free, Binder-Free MnO2@Mn Catalyst for Oxygen Reduction Reaction

Reasonable design and feasible preparation of low-cost and stable oxygen reduction reaction (ORR) catalysts with excellent performance play a key role in the development of fuel cells and metal-air batteries. A 3D porous superimposed nanosheet catalyst composed of metal manganese covered with MnO₂ nanofilms (P-NS-MnO₂@Mn) was designed and synthesized by rotating disk electrodes (RDEs) through one-step electrodeposition. The catalyst contains no carbon material. Therefore, the oxidation and corrosion of the carbon material during use can be avoided, resulting in excellent stability. The structural and composition characterizations indicate that the nanosheets with sharp edges exist on the surface of the wall surrounding the macropore (diameter ∼ 5.07 μm) and they connect tightly. Both the nanosheets and the wall of the macropore are composed of metal manganese covered completely with MnO₂ film with a thickness of less than 5 nm. The half-wave potential of the synthesized P-NS-MnO₂@Mn catalyst is 0.86 V. Besides, the catalyst exhibits good stability with almost no decay after a 30 h chronoamperometric test. Finite element analysis (FEA) simulation reveals the high local electric field intensity surrounding the sharp edges of the nanosheets. Density functional theory (DFT) calculations reveal that the novel nanosheet structure composed of MnO₂ nanofilms covered on the surface of the Mn matrix accelerates the electronic transfer of the MnO₂ nanofilms during the ORR process. The high local electric field intensity near the sharp edge of the nanosheets effectively promotes the orbital hybridization and strengthens the adsorbing Mn-O bond between the active site Mn in the nanosheets and the intermediate OOH* during the ORR process. This study provides a new strategy for preparing transition metal oxide catalysts and a novel idea about the key factors affecting the catalytic activity of transition metal oxides for the ORR.

Local Electric Field Induced by Atomic-Level Donor-Acceptor Couple of O Vacancies and Mn Atoms Enables Efficient Hybrid Capacitive Deionization

Transition metal oxides suffer from slow salt removal rate (SRR) due to inferior ions diffusion ability in hybrid capacitive deionization (HCDI). Local electric field (LEF) can efficiently improve the ions diffusion kinetics in thin electrodes for electrochemical energy storage. Nevertheless, it is still a challenge to facilitate the ions diffusion in bulk electrodes with high loading mass for HCDI. Herein, this work delicately constructs a LEF via engineering atomic-level donor (O vacancies)-acceptor (Mn atoms) couples, which significantly facilitates the ions diffusion and then enables a high-performance HCDI. The LEF boosts an extended accelerated ions diffusion channel at the particle surface and interparticle space, resulting in both remarkably enhanced SRR and salt removal capacity. Convincingly, the theoretical calculations demonstrate that electron-enriched Mn atoms center coupled with an electron-depleted O vacancies center is formed due to the electron back-donation from O vacancies to adjacent Mn centers. The resulted LEF efficiently reduce the ions diffusion energy barrier. This work sheds light on the effect of atomic-level LEF on improving ions diffusion kinetics at high loading mass application and paves the way for the design of transition metal oxides toward high-performance HCDI applications.

Zinc Single-Atom-Regulated Hard Carbons for High-Rate and Low-Temperature Sodium-Ion Batteries

Hard carbons, as one of the most commercializable anode materials for sodium-ion batteries (SIBs), have to deal with the trade-off between the rate capability and specific capacity or initial Columbic efficiency (ICE), and the fast performance decline at low temperature (LT) remains poorly understood. Here, a comprehensive regulation on the interfacial/bulk electrochemistry of hard carbons through atomic Zn doping is reported, which demonstrates a record-high reversible capacity (546 mAh g^-1 ), decent ICE (84%), remarkable rate capability (140 mAh g^-1 @ 50 A g^-1 ), and excellent LT capacity (443 mAh g^-1 @ -40 °C), outperforming the state-of-the-art literature. This work reveals that the Zn doping can generally induce a local electric field to enable fast bulk Na⁺ transportation, and meanwhile catalyze the decomposition of NaPF₆ to form a robust inorganic-rich solid-electrolyte interphase, which elaborates the underlying origin of the boosted electrochemical performance. Importantly, distinguished from room temperature, the intrinsic Na⁺ migration/desolvation ability of the electrolyte is disclosed to be the crucial rate-determining factors for the SIB performance at LT. This work provides a fundamental understanding on the charge-storage kinetics at varied temperatures.

Covalently Assembled Black Phosphorus/Conductive C3N4 Hybrid Material for Flexible Supercapacitors Exhibiting a Superlong 30,000 Cycle Durability

Black phosphorus (BP) has been demonstrated as a promising electrode material for supercapacitors. Currently, the main limitation of its practical application is the low electrical conductivity and poor structure stability. Hence, BP-based supercapacitors usually severely suffer from low capacitance and poor cycling stability. Herein, a chemically bridged BP/conductive g-C₃N₄ (BP/c-C₃N₄) hybrid is developed via a facile ball-milling method. Covalent P-C bonds are generated through the ball-milling process, effectively preventing the structural distortion of BP induced by ion transport and diffusion. In addition, the overall electrical conductivity is significantly enhanced owing to the sufficient coupling between BP and highly conductive c-C₃N₄. Moreover, the imbalanced charge distribution around the C atom can induce the generation of a local electric field, facilitating the charge transfer behavior of the electrode material. As a result, the BP/c-C₃N₄-20:1 flexible supercapacitor (FSC) exhibits an outstanding volumetric capacitance of 42.1 F/cm³ at 0.005 V/s, a high energy density of 5.85 mW h/cm³, and a maximum power density of 15.4 W/cm³. More importantly, the device delivers excellent cycling stability with no capacitive loss after 30,000 cycles.

Local Electric Field Promoted Kinetics and Interfacial Stability of a Phosphorus Anode with Ionic Covalent Organic Frameworks

A phosphorus anode is a promising option for energy-storage applications because of its high theoretical specific capacity and safe lithiation potential. However, the multiphase phosphorus lithiation/delithiation reactions and soluble reaction intermediates cause sluggish reaction kinetics and loss of active materials. Herein, a novel local electric field (LEF) strategy is proposed to inhibit the intermediates dissolution and promote the reaction kinetics by optimizing ionic covalent organic frameworks (iCOFs). Among them, the LEF induced by the cationic covalent organic framework effectively enhances the electrochemical performance of the phosphorus anode. The strong electrostatic interaction between the polyphosphides and cationic covalent organic framework confines the dissolution of active materials and tailors the electronic structure of polyphosphides to accelerate the reaction kinetics. The cationic covalent-organic-framework-assisted phosphorus anode provides a high capacity of 1227.8 mAh g^-1 at 10.4 A g^-1 (8.6 C) and a high-capacity retention of 87% after 500 cycles at 1.3 A g^-1 . This work not only broadens the application of iCOFs for phosphorus anode but also inspires the great potential of the local electric field in battery technology.

Local Electric Field Controls Fluorescence Quantum Yield of Red and Far-Red Fluorescent Proteins

Genetically encoded probes with red-shifted absorption and fluorescence are highly desirable for imaging applications because they can report from deeper tissue layers with lower background and because they provide additional colors for multicolor imaging. Unfortunately, red and especially far-red fluorescent proteins have very low quantum yields, which undermines their other advantages. Elucidating the mechanism of nonradiative relaxation in red fluorescent proteins (RFPs) could help developing ones with higher quantum yields. Here we consider two possible mechanisms of fast nonradiative relaxation of electronic excitation in RFPs. The first, known as the energy gap law, predicts a steep exponential drop of fluorescence quantum yield with a systematic red shift of fluorescence frequency. In this case the relaxation of excitation occurs in the chromophore without any significant changes of its geometry. The second mechanism is related to a twisted intramolecular charge transfer in the excited state, followed by an ultrafast internal conversion. The chromophore twisting can strongly depend on the local electric field because the field can affect the activation energy. We present a spectroscopic method of evaluating local electric fields experienced by the chromophore in the protein environment. The method is based on linear and two-photon absorption spectroscopy, as well as on quantum-mechanically calculated parameters of the isolated chromophore. Using this method, which is substantiated by our molecular dynamics simulations, we obtain the components of electric field in the chromophore plane for seven different RFPs with the same chromophore structure. We find that in five of these RFPs, the nonradiative relaxation rate increases with the strength of the field along the chromophore axis directed from the center of imidazolinone ring to the center of phenolate ring. Furthermore, this rate depends on the corresponding electrostatic energy change (calculated from the known fields and charge displacements), in quantitative agreement with the Marcus theory of charge transfer. This result supports the dominant role of the twisted intramolecular charge transfer mechanism over the energy gap law for most of the studied RFPs. It provides important guidelines of how to shift the absorption wavelength of an RFP to the red, while keeping its brightness reasonably high.

Disaggregation of Amyloid-β Plaques by a Local Electric Field Generated by a Vertical Nanowire Electrode Array

The aggregation and accumulation of amyloid-β (Aβ) peptides is a characteristic pathology for Alzheimer's disease (AD). Although noninvasive therapies involving stimulation by electric field (EF) have been reported, the efficiency of Aβ disaggregation needs to be further improved for this strategy to be used in clinical settings. In this study, we show that an electrode based on a vertical nanowire electrode array (VNEA) is far more superior to a typical flat-type electrode in disaggregating Aβ plaques. The enhanced disaggregation efficiency of VNEA is due to the formation of high-strength local EF between the nanowires, as verified by in silico and empirical evidence. Compared with those of the flat electrode, the simulation data revealed that 19.8-fold and 8.8-fold higher EFs are generated above and between the nanowires, respectively. Moreover, empirical cyclic voltammetry data demonstrated that VNEA had a 2.7-fold higher charge capacity than the flat electrode; this is associated with the higher surface area of VNEA. The conformational transition of Aβ peptides between the β-sheet and α-helix could be sensitively monitored in real time by the newly designed in situ circular dichroism instrument. This highly efficient EF-configuration of VNEA will lower the stimulation power for disaggregating the Aβ plaques, compared to that of other existing field-mediated modulation systems. Considering the complementary metal-oxide-semiconductor-compatibility and biocompatible strength of the EF for perturbing the Aβ aggregation, our study could pave the way for the potential use of electric stimulation devices for in vivo therapeutic application as well as scientific studies for AD.

Measuring Local Electric Fields and Local Charge Densities at Electrode Surfaces Using Graphene-Enhanced Raman Spectroscopy (GERS)-Based Stark-Shifts

We report spectroscopic measurements of the local electric fields and local charge densities at electrode surfaces using graphene-enhanced Raman spectroscopy (GERS) based on the Stark-shifts of surface-bound molecules and the G band frequency shift in graphene. Here, monolayer graphene is used as the working electrode in a three-terminal potentiostat while Raman spectra are collected in situ under applied electrochemical potentials using a water immersion lens. First, a thin layer (1 Å) of copper(II) phthalocyanine (CuPc) molecules are deposited on monolayer graphene by thermal evaporation. GERS spectra are then taken in an aqueous solution as a function of the applied electrochemical potential. The shifts in vibrational frequencies of the graphene G band and CuPc are obtained simultaneously and correlated. The upshifts in the G band Raman mode are used to determine the free carrier density in the graphene sheet under these applied potentials. Of the three dominant peaks in the Raman spectra of CuPc (i.e., 1531, 1450, and 1340 cm^-1), only the 1531 cm^-1 peak exhibits Stark-shifts and can, thus, be used to report the local electric field strength at the electrode surface under electrochemical working conditions. Between applied electrochemical potentials from -0.8 V to 0.8 V vs NHE, the free carrier density in the graphene electrode spans a range from -4 × 10¹² cm^-2 to 2 × 10¹² cm^-2. Corresponding Stark-shifts in the CuPc peak around 1531 cm^-1 are observed up to 1.0 cm^-1 over a range of electric field strengths between -3.78 × 10⁶ and 1.85 × 10⁶ V/cm. Slightly larger Stark-shifts are observed in a 1 M KCl solution, compared to those observed in DI water, as expected based on the higher ion concentration of the electrolyte. Based on our data, we determine the Stark shift tuning rate to be 0.178 cm^-1/ (10⁶ V/cm), which is relatively small due to the planar nature of the CuPc molecule, which largely lies perpendicular to the electric field at this electrode surface. Computational simulations using density functional theory (DFT) predict similar Stark shifts and provide a detailed atomistic picture of the electric field-induced perturbations to the surface-bound CuPc molecules.

Local Electric Field Facilitates High-Performance Li-Ion Batteries

By scrutinizing the energy storage process in Li-ion batteries, tuning Li-ion migration behavior by atomic level tailoring will unlock great potential for pursuing higher electrochemical performance. Vacancy, which can effectively modulate the electrical ordering on the nanoscale, even in tiny concentrations, will provide tempting opportunities for manipulating Li-ion migratory behavior. Herein, taking CuGeO₃ as a model, oxygen vacancies obtained by reducing the thickness dimension down to the atomic scale are introduced in this work. As the Li-ion storage progresses, the imbalanced charge distribution emerging around the oxygen vacancies could induce a local built-in electric field, which will accelerate the ions' migration rate by Coulomb forces and thus have benefits for high-rate performance. Furthermore, the thus-obtained CuGeO₃ ultrathin nanosheets (CGOUNs)/graphene van der Waals heterojunctions are used as anodes in Li-ion batteries, which deliver a reversible specific capacity of 1295 mAh g^-1 at 100 mA g^-1, with improved rate capability and cycling performance compared to their bulk counterpart. Our findings build a clear connection between the atomic/defect/electronic structure and intrinsic properties for designing high-efficiency electrode materials.

Resistive Switching and the Local Electric Field in Bi0.85-xPr0.15RExFe0.97Mn0.03O3/CuFe2O4 (RE = Sr, Dy) Bilayered Thin Films

Bilayer Bi_0.85-xPr_0.15RE_xFe_0.97Mn_0.03O₃/CuFe₂O₄ (BPRE_xFMO/CuFO, RE = Sr, Dy) thin films were prepared on FTO/glass substrates by the chemical solution deposition method. The structure transition does not appear after ion doping, which is confirmed by XRD and its refined results. The samples remain in the trigonal R3c:H structure in the BFO phase and in the tetragonal I41/amd structure in the CuFO phase. The asymmetric character of leakage current density curves and resistive switching effects have been explored. And the ion substitution impacts on the resistive switching effects may be due to the existence of local fields. Under the applied electric field, carries are accumulated and arranged directionally at the interface between the BFO and CuFO layers to form the local electric field. Such local field is affected by ion dopants, and the field compensates or weakens the applied electrical field. The reinforced or weakened resistive behavior is dependent on the direction of the local field and the injection of electrons. The polarization switching currents of the BPFMO/CuFO, BPSFMO/CuFO, and BPDFMO/CuFO samples, whose distribution fields are proportional to the local electrical fields, are 0.0070, 0.0049, and 0.0074 A under the positive applied field, respectively. And the remanent polarization is increased to 74.4, 73.5, and 84.3 μC/cm² of the doped samples, respectively.

Nature of the Enhancement in Ferroelectric Properties by Gold Nanoparticles in Vinylidene Fluoride and Trifluoroethylene Copolymer

Ferroelectric polymers are a candidate for versatile and cheap data storage memory devices, with easy processing for a large-scale device. Easy switching and large remanent polarization of preferentially formed β-crystal dipoles in a copolymer of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) are promising properties for versatile memory devices. At higher frequency switching, however, the remanent polarization is reduced and a high coercive field, an electric field for polarization switching is required. The addition of a small amount of nanoparticles (NPs) significantly improves these ferroelectric properties in fluoropolymers. Here, we show that the addition of NPs of gold (Au), silver (Ag), and silicon oxide (SiO2) enhanced the ferroelectric properties in P(VDF-TrFE). AuNPs significantly affected a 40% increase of the remanent polarization, 14% reduction of the coercive field, and 100% increase of the switching speed of ferroelectric polarization. The nature of these enhancements due to the addition of NPs is verified. A higher shift of the binding energy of Au (4f7/2 and 4f5/2) and an increase of the fluorine ion (F(-)) was observed in AuNP-doped P(VDF-TrFE). Strong interactions between the AuNPs and the ferroelectric backbone gave rise to the formation of the interfacial polarization, which induced the local electric field to enhance the ferroelectric properties of the increment of the remanent polarization, the reduction of the coercive field, and faster switching speed.

Molecular-Level Insight into the Spectral Tuning Mechanism of the DsRed Chromophore

We present a detailed study of the protein environmental effects on the one- and two-photon absorption (1PA and 2PA, respectively) properties of the S0-S1 transition in the DsRed protein using the polarizable embedding density functional theory formalism. We find that steric factors and chromophore-protein interactions act in concert to enhance the 2PA activity inside the protein while adversely blue-shifting the 1PA maximum. A two-state model reveals that the 2PA intensity gain is primarily governed by the increased change in the permanent dipole moment between the ground and the excited states acquired inside the protein. Our results indicate that this mainly is attributable to counter-directional contributions stemming from Lys163 and the conserved Arg95 with the former additionally identified as a key residue in the color tuning mechanism. The results provide new insight into the tuning mechanism of DsRed and suggest a possible strategy for simultaneous improvement of its 1PA and 2PA properties.