Helmholtz Layer Research Articles

Hansen Solubility Parameter-Guided Solvent Selection for Solution-Phase Discharge in Li-CO2 Batteries.

Surface discharge mechanism-induced cathode passivation is a critical challenge that blocks the full liberation of the ultrahigh theoretical energy density of Li-CO2 batteries. Herein, we propose a novel concept based on Hansen solubility parameters (HSPs) to guide the selection of solvents for inducing the dissolution of discharge products, facilitating the detachment of in situ-formed metastable Li2C2O4 from the electrode surface and enabling a continuous Li2C2O4-dominated discharge process. Combining theoretical calculations with HSP predictions, we identified Pd-OCNTs as an ideal catalyst, with tetraethylene glycol dimethyl ether as the optimal solvent for Li2C2O4 production and stabilization. This combination facilitates the rapid diffusion of Li2C2O4 generated in situ near the catalyst surface out of the inner Helmholtz layer. Consequently, the system exhibits high energy efficiency of 96.7% and remarkable stability over 3200 h. This work provides critical insights into the solution-mediated dissolution process of Li2C2O4, informing strategies for multiphase interfacial reactions in Li-CO2 batteries.

Ferroelectric Dipoles Tailoring Solid‐Electrolyte‐Interphase Chemistry to Enable Reversible Lithium Metal Batteries

AbstractSolid‐electrolyte interphase (SEI) plays a decisive role in building reliable Li metal batteries. However, the scarcity of anions in Helmholtz layer (HL) caused by electrostatic repulsion usually leads to the inferior SEI derived from solvents, resulting in dendrites and ‘dead’ Li. Therefore, regulating the distribution of anions in electric double layer (EDL) and continuously introducing more anions into HL to tailor anions‐derived SEI is crucial for achieving stable Li plating/stripping. Herein, by jointly utilizing the controlled defects of reduced graphene oxide (rGO) and the oriented dipoles of ferroelectric BaTiO3 (BTO), the rGO‐BTO composite layer sustainedly brings more TFSI− and NO3− into anion‐defecient HL, promoting favorable decomposition of anions and guiding the generation of robust and fast‐Li+‐transport SEI containing more inorganics LiF and Li3N species. Thus, the resulting Li deposit shows smooth and dense morphologies without dendrites, leading to high average Coulombic efficiency. The Li//Cu@rGO‐BTO (10 mAh cm−2 plated Li) cell exhibits an enhanced Li plating/stripping stability (2700 h) and a higher rate capability. The LiFePO4 full cell (N/P≈6.3) using rGO‐BTO displays an enhanced capacity retention (82.0 % @ 430 cycles). This work provides a new insight on the construction of robust SEI by regulating the distribution of anions within EDL.

Weak solvation effects and molecular-rich layers induced water-poor Helmholtz layers boost highly stable Zn anode

The advancement of aqueous Zn-based energy storage systems encounters major challenges due to the occurrence of side reactions and the growth of dendrites caused by the highly active nature of water in the aqueous electrolyte. Herein, a zwitterion additive named sulfonated amphoteric betaine (referred to as DMAPS) regulates the Zn2+ electrolyte environment through a weak solvation effect to promote highly stable Zn anodes. The inherently occurring anionic (-SO3-) and cationic (-NR4+) counterions in the DMAPS chain can be effectively separated under an external electric field to enable the creation of distinct ion migration pathways, thereby significantly enhancing the transportation of electrolyte ions. Moreover, DMAPS can be adsorbed onto the surface of Zn anode to form a H2O-poor Helmholtz layer, which can serve as a protective barrier to suppress corrosion of the Zn anode by free H2O and inhibits the formation of differential electric field to facilitate the directional deposition of Zn2+. In addition, density functional theory (DFT) and molecular dynamics (MD) further assisted in demonstrating the intrinsic mechanism of the reconstruction of the solvated sheath structure of Zn2+ by DMAPS. As a result, the Zn//Zn symmetric cell in ZnSO4+DMAPS solution can be cycled steadily for 2100 h at a current density of 1 mA cm-2 and 1 mAh cm-2. The assembled Zn ion hybrid capacitor with ZnSO4+DMAPS electrolyte was stably cycled for 20,000 cycles with 90% capacity retention at 5 A g-1.

Stable Zn‐Metal Anode Enabled by Solvation Structure Modulation and In‐Situ SEI Layer Construction

Aqueous zinc‐ion batteries encounter impediments on their trajectory towards commercialization, primarily due to challenges such as dendritic growth, hydrogen evolution reaction. Throughout recent decades of investigation, electrolyte modulation by using function additives is widely considered as a facile and efficient way to prolong the Zn anode lifespan. Herein, N‐(2‐hydroxypropyl)ethylenediamine is employed as an additive to attach onto the Zn surface with a substantial adsorption energy with (002) facet. The as‐formed in‐situ solid‐electrolyte interphase layer effectively mitigates hydrogen evolution reaction by constructing a lean‐water internal Helmholtz layer. Additionally, N‐(2‐hydroxypropyl)ethylenediamine establishes a coordination complex with Zn2+, thereby modulating the solvation structure and enhancing the mobility of Zn2+. As expected, the Zn‐symmetrical cell with N‐(2‐hydroxypropyl)ethylenediamine additive demonstrated successful cycling exceeding 1500 h under 1 mA cm−2 for 0.5 mAh cm−2. Furthermore, the Zn//δ‐MnO2 battery maintains a capacity of approximately 130 mAh g−1 after 800 cycles at 1 A g−1, with a Coulombic efficiency surpassing 98%. This work presents a streamlined approach for realizing aqueous zinc‐ion batteries with extended service life.

Hydrogen bonding network in the electrical double layer mediates fast proton skipping to Get Rid of Fenton reaction pH dependence enables highly efficient alkaline water purification

A fundamental scientific quandary in environmental has always been the pH dependence in Fenton reaction, that is, the reaction kinetics decreases by approximately 1–3 orders of magnitude upon transitioning from an acidic to an alkaline state. Here, we discovered that protons significantly contribute to the Fenton reaction through an examination of the reaction's interfacial behavior characteristics. Proton transfer mediated by hydrogen bond network connectivity in the electric double layer is responsible for the pH dependence of Fenton reaction kinetics. On this basis, the surface potential of Fenton reaction catalyst was modified to optimize the distribution of H2O in the electrical double layer, enhancing the connectivity of the interfacial hydrogen bond network and providing a fast channel for rapid proton transfer. The consecutive hydrogen bond network mediates rapid proton hopping, increasing the proton concentration in the Helmholtz layer, and consequently promoting the proton conductivity from 5.38×10−7 S·cm−2 to 4.35×10−6 S·cm−2 in alkaline conditions for Fenton reaction. Meanwhile, the kinetics reaction rate was improved 20 times, and the pH dependence was reduced from 70.9 % to 12.6 %. This discovery clarifies the key role of the interfacial hydrogen bond network and proton transfer in Fenton reaction kinetics pH dependence. It provides new theories and methods for achieving alkaline high Fenton reaction kinetics.

Ferroelectric Dipoles Tailoring Solid-Electrolyte-Interphase Chemistry to Enable Reversible Lithium Metal Batteries.

Solid-electrolyte interphase (SEI) plays a decisive role in building reliable Li metal batteries. However, the scarcity of anions in Helmholtz layer (HL) caused by electrostatic repulsion usually leads to the inferior SEI derived from solvents, resulting in dendrites and 'dead' Li. Therefore, regulating the distribution of anions in electric double layer (EDL) and continuously introducing more anions into HL to tailor anions-derived SEI is crucial for achieving stable Li plating/stripping. Herein, by jointly utilizing the controlled defects of reduced graphene oxide (rGO) and the oriented dipoles of ferroelectric BaTiO3 (BTO), the rGO-BTO composite layer sustainedly brings more TFSI- and NO3 - into anion-defecient HL, promoting favorable decomposition of anions and guiding the generation of robust and fast-Li+-transport SEI containing more inorganics LiF and Li3N species. Thus, the resulting Li deposit shows smooth and dense morphologies without dendrites, leading to high average Coulombic efficiency. The Li//Cu@rGO-BTO (10 mAh cm-2 plated Li) cell exhibits an enhanced Li plating/stripping stability (2700 h) and a higher rate capability. The LiFePO4 full cell (N/P≈6.3) using rGO-BTO displays an enhanced capacity retention (82.0 % @ 430 cycles). This work provides a new insight on the construction of robust SEI by regulating the distribution of anions within EDL.

Revealing capacitive behaviors of graphene in ionic liquids using molecular dynamics simulation

Abstract This work reveals the capacitive behaviors of graphene nanomaterials in typical ionic liquids of [BMI+] [BF4 −] using molecular dynamics simulations. It is found that the charging process induces a structural transition from disordered to partially ordered and then ordered multilayer structures of [BMI+][BF4 −] electrolyte, yielding a multiple layer-by-layer packing structure of BMI+ cation and BF4 − anion. Especially, a counterion-adsorption-dominated Helmholtz layer is revealed at a high charge density of 16 μC/cm2, which is primarily responsible for the superior capacitance results. Besides, the differential capacitance of [BMI+][BF4 −] exhibits a symmetric convexity-shaped curve, showing a maximal capacitance value of 4.83 μF/cm2. The as-obtain simulation results help to understand the microscopic charge storage mechanisms of graphene in ionic liquids.

Kinetics of Charge Reversal in the Double Layer Studied with an Electrochemical Quartz Crystal Microbalance (EQCM-D)

Normal pulse voltammetry on inert electrolytes was combined with a new electrochemical quartz crystal microbalance (EQCM) with millisecond time resolution, which allows to probe the kinetics of charge reversal in the diffuse double layer (DL) after a step in electrode potential. The QCM responds to the charge reversal because the local viscosity-density product depends on the type and the concentration of the ions. The time resolution was improved to 1 ms using multifrequency lockin amplification, which allows to study kinetic effects in dynamic electrochemistry, which were previously not accessible with gravimetry. The noise was lowered to less than 10 mHz by modulating the electrode potential and averaging Δf and ΔΓ over many modulation cycles.The overtone scaling was found to be the same as in gravimetry (-Δf/n » const. and ΔΓ/n < -Δf/n with n the overtone order), which, however, is not caused by a deposition of a rigid film in the Sauerbrey sense. A Sauerbrey-type QCM response is also caused by changes in Newtonian viscosity inside a layer with a thickness far below the penetration depth of the shear wave (such as the double layer).The frequency response in the electrolytes studied correlated well with the viscosity B-coefficients of the respective ions as employed in the Dole-Jones equation. The time constants inferred from gravimetry were similar to the time constants (the RC-times) from electrochemical impedance spectroscopy (EIS). There were small differences, which presumably go back to slow rearrangements inside the Helmholtz layer, which are not seen in EIS.The QCM response to double layer recharging in inert electrolytes is of great importance for the interpretation of QCM results on processes involving Faradayic charge transfer. Such a response is omnipresent as a background and might be misinterpreted as a gravimetric signal.[1] References[1] Leppin, C.; Peschel, A.; Meyer, F. S.; Langhoff, A.; Johannsmann, D. Kinetics of Viscoelasticity in the Electric Double Layer Following Steps in the Electrode Potential Studied by a Fast Electrochemical Quartz Crystal Microbalance (EQCM). Analyst 2021, 146 (7), 2160–2171. Caption: Shifts in frequency and bandwidth in response to potential steps (left). The gravimetric signal followed the steps with a delay of a few milliseconds. The amplitude and the response time depend on cation type (right). The counter ion was NO3 -. Both the amplitude and the response time correlate well with the viscosity B-coefficient. Figure 1

Regulating interfacial behavior via reintegration the Helmholtz layer structure towards ultra-stable and wide-temperature-range aqueous zinc ion batteries

Aqueous zinc-ion batteries are recognized as a potential candidate in large-scale energy storage devices. However, parasitic reactions on interfaces have severely limited their further development due to sticky de-solvation process of Zn(H2O)62+. Acetylacetone (Hacac) is proposed as a tri-functional additive by altering the solvation structure to address detrimental interface issues. Specifically, the acetyl groups induced by decomposition of Hacac inhibit dendrite growth, by-product aggregation on anode via guiding ordered deposition of zinc ions and suppressing water decomposition in internal Helmholtz plane (IHP). Meanwhile, the acetyl groups remarkably alleviate by-product aggregation and maintain the cathode structure by accelerating zinc ion transfer and inhibiting disintegration of water in IHP. With the addition of 0.5 wt% Hacac, Zn metal maintains a high coulombic efficiency of 99.9 % after 2000 cycles at 10 mA cm−2 and 1 mAh cm−2, with superior longevity of 5200 h at 1 mA cm−2 with 0.5 mAh cm−2 for Zn|Zn cells. As expected, the assembled Zn|NH4V4O10 batteries exhibit an outstanding capacity retention of 90 % up to 22,000 cycles at 10 A/g. As a highly efficient strategy, the reframing of Helmholtz layer structure via electrolyte additive could be broadened to address general interfacial issues in advanced energy storage systems.

Anionic Aggregates Induced Interphase Chemistry Regulation toward Wide‐Temperature Silicon‐Based Batteries

AbstractSilicon nanoparticles (SiNPs) show great promise as high‐capacity anodes owing to their ability to mitigate mechanical failure. However, the substantial surface area of SiNPs triggers interfacial side reactions and solid electrolyte interphase (SEI) permeation during volume fluctuations. The slow kinetics at low temperatures and the degradation of SEI at high temperatures further hinder the practical application of SiNPs in real‐world environments. Here, these challenges are addressed by manipulating the solvation structure through molecular space hindrance. The electrolyte enables anions to aggregate in the outer Helmholtz layer under an electric field, leading to rapid desolvation capabilities and the formation of anion‐derived SEI. The resulting double‐layer SEI, where inorganic nano‐clusters are uniformly dispersed in the amorphous structure, completely encapsulates the particles in the first cycle. The ultra‐high modulus of this structure can withstand stress accumulation, preventing electrolyte penetration during repeated expansion and contraction. As a result, SiNPs‐based batteries demonstrate exceptional electrochemical performance across a wide temperature range from −20 to 60 °C. Moreover, the assembled 80 mAh SiNPs/LiFePO4 pouch cells maintain a cycling retention of 85.6% after 150 cycles, marking a significant step forward in the practical application of silicon‐based batteries.

Quantitative Analysis of the Synergy of Doping and Nanostructuring of Oxide Photocatalysts.

In this paper, the effect of doping and nanostructuring on the electrostatic potential across the electrochemical interface between a transition metal oxide and a water electrolyte is investigated by means of the Poisson-Boltzmann model. For spherical nanoparticles and nanorods, compact expressions for the limiting potentials at which the space charge layer includes the whole semiconductor are reported. We provide a quantitative analysis of the distribution of the potential drop between the solid and the liquid and show that the relative importance changes with doping. It is usually assumed that high doping improves charge dynamics in the semiconductor but reduces the width of the space charge layer. However, nanostructuring counterbalances the latter negative effect; we show quantitatively that in highly doped nanoparticles the space charge layer can occupy a similar volume fraction as in low-doped microparticles. Moreover, as shown by some recent experiments, under conditions of high doping the electric fields in the Helmholtz layer can be as high as 100 mV/Å, comparable to electric fields inducing freezing in water. This work provides a systematic quantitative framework for understanding the effects of doping and nanostructuring on electrochemical interfaces, and suggests that it is necessary to better characterize the interface at the atomistic level.

The zinc ion concentration dynamically regulated by an ionophore in the outer Helmholtz layer for stable Zn anode

The Zn dendrite limits the practical application of aqueous zinc-ion batteries in the large-scale energy storage systems. To suppress the growth of Zn dendrites, a zinc ionophore of hydroxychloroquine (defined as HCQ) applied in vivo treatment is investigated as the electrolyte additive. HCQ dynamically regulates zinc ion concentration in the outer Helmholtz layer, promoting even Zn plating at the anode/electrolyte interface. This is evidenced by the scanning electron microscopy, which delivers planar Zn plating after cycling. It is further supported by the X-ray diffraction spectroscopy, which reveals the growth of Zn (002) plane. Additionally, the reduced production of H2 during Zn plating/stripping is detected by the in-situ differential electrochemical mass spectrometry (DEMS), which shows the resistance of Zn (002) to hydrogen evolution reaction. The mechanism of dynamic regulation for zinc ion concentration is demonstrated by the in-situ optical microscopy. The hydrated zinc ion can be further plated more rapidly to the uneven location than the case in other regions, which is resulted from the dynamic regulation for zinc ion concentration. Therefore, the uniform Zn plating is formed. A cycling life of 1100 h is exhibited in the Zn||Zn symmetric cell at 1.6 mA cm−2 with the capacity of 1.6 mAh cm−2. The Zn||Cu battery exhibits a cycling life of 200 cycles at 4 mA cm−2 with a capacity of 4 mAh cm−2 and the average Coulombic efficiency is larger than 99 %. The Zn||VO2 battery with HCQ modified electrolyte can operate for 1500 cycles at 4 A g−1 with a capacity retention of 90 %. This strategy in the present work is wished to advance the development of zinc-ion batteries for practical application.

Partially solvated cosolvent induced reconfiguration of solvation structure and Helmholtz layer for lithium metal battery

Reconfiguring the electrolyte microstructure containing Li+ solvation structure in bulk electrolyte and Helmholtz layer (HL) near the interface presents a compelling strategy in the design of electrolytes. In this work, ionic liquids (ILs) and partially solvated fluorobenzene (FB) build the unique Li+ coordination state modulated by FB and dominated by anions as well as a HL enriched in non-sacrificial cations on charging. As an important part to regulate the micro environment, FB not only enhances the ion transport kinetics of electrolyte and promotes the interaction of Li+-FSI−, but also participates in constructing a robust solid electrolyte interphase (SEI). Interestingly, FB indirectly promotes the enrichment of ILs’ cations at the HL, which is beneficial for uniform Li metal deposition due to its electrostatic shielding effect. Lithium metal batteries utilizing this electrolyte demonstrate impressive cycling performance at a high rate (approximately 89% capacity retention after 2,500 cycles at 5 C). Furthermore, these cells show excellent high-temperature performance, maintaining 71% of the initial capacity after 1,000 cycles at 70°C and 10 C rate.

Electric Double Layer Regulator Design through a Functional Group Assembly Strategy towards Long‐Lasting Zinc Metal Batteries

AbstractRegulating the electric double layer (EDL) structure of the zinc metal anode by using electrolyte additives is an efficient way to suppress interface side reactions and facilitate uniform zinc deposition. Nevertheless, there are no reports investigating the proactive design of EDL‐regulating additives before the start of experiments. Herein, a functional group assembly strategy is proposed to design electrolyte additives for modulating the EDL, thereby realizing a long‐lasting zinc metal anode. Specifically, by screening ten common functional groups, N, N‐dimethyl‐1H‐imidazole‐1‐sulfonamide (IS) is designed by assembling an imidazole group, characterized by its high adsorption capability on the zinc anode, and a sulfone group, which exhibits strong binding with Zn2+ ions. Benefiting from the adsorption functionalization of the imidazole group, the IS molecules occupy the position of H2O in the inner Helmholtz layer of the EDL, forming a molecular protective layer to inhibit H2O‐induced side reactions. Meanwhile, the sulfone group in IS, acting as a binding site to Zn2+, promotes the de‐solvation of Zn2+ ions, facilitating compact zinc deposition. Consequently, the utilization of IS significantly extending the cycling stability of Zn||Zn and Zn||NaV3O8 ⋅ 1.5H2O full cell. This study offers an innovative approach to the design of EDL regulators for high‐performance zinc metal batteries.

Electric Double Layer Regulator Design through a Functional Group Assembly Strategy towards Long-Lasting Zinc Metal Batteries.

Regulating the electric double layer (EDL) structure of the zinc metal anode by using electrolyte additives is an efficient way to suppress interface side reactions and facilitate uniform zinc deposition. Nevertheless, there are no reports investigating the proactive design of EDL-regulating additives before the start of experiments. Herein, a functional group assembly strategy is proposed to design electrolyte additives for modulating the EDL, thereby realizing a long-lasting zinc metal anode. Specifically, by screening ten common functional groups, N, N-dimethyl-1H-imidazole-1-sulfonamide (IS) is designed by assembling an imidazole group, characterized by its high adsorption capability on the zinc anode, and a sulfone group, which exhibits strong binding with Zn2+ ions. Benefiting from the adsorption functionalization of the imidazole group, the IS molecules occupy the position of H2O in the inner Helmholtz layer of the EDL, forming a molecular protective layer to inhibit H2O-induced side reactions. Meanwhile, the sulfone group in IS, acting as a binding site to Zn2+, promotes the de-solvation of Zn2+ ions, facilitating compact zinc deposition. Consequently, the utilization of IS significantly extending the cycling stability of Zn||Zn and Zn||NaV3O8 ⋅ 1.5H2O full cell. This study offers an innovative approach to the design of EDL regulators for high-performance zinc metal batteries.

Superdiffusive Rotation of Interfacial Water on Noble Metal Surface.

Interfacial water on a metal surface acts as an active layer through the reorientation of water, thereby facilitating the energy transfer and chemical reaction across the metal surface in various physicochemical and industrial processes. However, how this active interfacial water collectively behaves on flat noble metal substrates remains largely unknown due to the experimental limitation in capturing librational vibrational motion of interfacial water and prohibitive computational costs at the first-principles level. Herein, by implementing a machine-learning approach to train neural network potentials, we enable performing advanced molecular dynamics simulations with ab initio accuracy at a nanosecond scale to map the distinct rotational motion of water molecules on a metal surface at room temperature. The vibrational density of states of the interfacial water with two-layer profiles reveals that the rotation and vibration of water within the strong adsorption layer on the metal surface behave as if the water molecules in the bulk ice, wherein the O-H stretching frequency is well consistent with the experimental results. Unexpectedly, the water molecules within the adjacent weak adsorption layer exhibit superdiffusive rotation, contrary to the conventional diffusive rotation of bulk water, while the vibrational motion maintains the characteristic of bulk water. The mechanism underlying this abnormal superdiffusive rotation is attributed to the translation-rotation decoupling of water, in which the translation is restrained by the strong hydrogen bonding within the bilayer interfacial water, whereas the rotation is accelerated freely by the asymmetric water environment. This superdiffusive rotation dynamics may elucidate the experimentally observed large fluctuation of the potential of zero charge on Pt and thereby the conventional Helmholtz layer model revised by including the contribution of interfacial water orientation. The surprising superdiffusive rotation of vicinal water next to noble metals will shed new light on the physicochemical processes and the activity of water molecules near metal electrodes or catalysts.

A kinetics-based approach to the steady-state and impedance response of photoelectrodes

A kinetics-based analytical model is developed to describe the steady-state and impedance response of photoelectrodes in the case where charge carrier build-up modifies the potential distribution across the semiconductor-electrolyte junction. The predictions of the steady-state model are compared with numerical calculations. It is shown that carrier build up should accelerate interfacial hole transfer by increasing the potential drop across the Helmholtz layer. This effect may explain observations of higher reaction orders with respect to hole concentration during photoelectrochemical oxygen evolution. The analytical model is extended to photoelectrochemical impedance spectroscopy (PEIS). The calculations indicate that interpretation of PEIS measurements becomes more complicated if high illumination intensities are used. The modeling of the analytically calculated PEIS response using equivalent circuits is discussed with the aim of understanding the physical significance of the resistive and capacitive elements.

Modulating inner Helmholtz layer by electrocatalytically sieving [Zn(H2O)6]2+ for 10000-cycle zinc-ion hybrid capacitors under extremely harsh conditions

Zinc-ion hybrid capacitors (ZIHCs) are famous for potential applications in grid-scale energy storage devices with fast-charge capability. However, their industrialization is severely plagued by inferior performance caused by the sluggish Zn2+ desolvation kinetics with large spatial diffusion hinderance of [Zn(H2O)6]2+ in the inner Helmholtz plane (IHP) layer, especially under low-temperature surroundings. Herein, the simultaneous rapid desolvation strategy via pore sieving and electrocatalysis is initially proposed to promote [Zn(H2O)6]2+ dissociation, regulating the isolated Zn2+ behaviors in the IHP. Specifically, heteroatom-decorated carbon microspheres with multi-level channels modulate the local distribution of electronic density, generating abundant catalytic sites to drive the kinetics of [Zn(H2O)6]2+ desolvation and free Zn2+ diffusion. Impressively, the catalytic desolvation behaviors and storage mechanism of ZIHCs are comprehensively investigated using in-situ electrochemical quartz crystal microbalance and various ex-situ/in-situ measurements as well as theoretical simulations, revealing significant interactions of isolated Zn2+ in the IHP. Consequently, the assembled ZIHCs exhibit a superior capacity of 177.2 mAh g−1, corresponding to a high energy density of 158.8 Wh kg−1, and provide a power density as high as 15.7 kW kg−1. Exposed to extreme environment, the ZIHCs encountered with severe solvation structure stabilize for 10000 cycles withcapacity retention of 99.42%, providing new insights of catalytically sieving into modulating IHP for high-performance ZIHCs under extreme conditions.

Generalized Helmholtz model describes capacitance profiles of ionic liquids and concentrated aqueous electrolytes.

In this work, we propose and validate a generalization of the Helmholtz model that can account for both "bell-shaped" and "camel-shaped" differential capacitance profiles of concentrated electrolytes, the latter being characteristic of ionic liquids. The generalization is based on introducing voltage dependence of both the dielectric constant "ϵr(V)" and thickness "L(V)" of the inner Helmholtz layer, as validated by molecular dynamics (MD) simulations. We utilize MD simulations to study the capacitance profiles of three different electrochemical interfaces: (1) graphite/[BMIm+][BF4-] ionic liquid interface; (2) Au(100)/[BMIm+][BF4-] ionic liquid interface; (3) Au(100)/1M [Na+][Cl-] aqueous interface. We compute the voltage dependence of ϵr(V) and L(V) and demonstrate that the generalized Helmholtz model qualitatively describes both camel-shaped and bell-shaped differential capacitance profiles of ionic liquids and concentrated aqueous electrolytes (in lieu of specific ion adsorption). In particular, the camel-shaped capacitance profile that is characteristic of ionic liquid electrolytes arises simply from combination of the voltage-dependent trends of ϵr(V) and L(V). Furthermore, explicit analysis of the inner layer charge density for both concentrated aqueous and ionic liquid double layers reveal similarities, with these charge distributions typically exhibiting a dipolar region closest to the electrode followed by a monopolar peak at larger distances. It is appealing that a generalized Helmholtz model can provide a unified description of the inner layer structure and capacitance profile for seemingly disparate aqueous and ionic liquid electrolytes.

CuO/Co3O4 Bifunctional Catalysts for Electrocatalytic 5‐Hydroxymethylfurfural Oxidation Coupled Cathodic Ammonia Production

The electrochemical coupling of biomass oxidation and nitrogen conversion presents a potential strategy for high value‐added chemicals and nitrogen cycling. Herein, in this work, CuO/Co3O4 with heterogeneous interface is successfully constructed as a bifunctional catalyst for the electrooxidation of 5‐hydroxymethylfurfural to 2,5‐furandicarboxylic acid and the electroreduction of nitrate to ammonia (NH3). The open‐circuit potential spontaneous experiment shows that more 5‐hydroxymethylfurfural molecules are adsorbed in the Helmholtz layer of the CuO/Co3O4 composite, which certifies that the CuO/Co3O4 heterostructure is conducive to the kinetic adsorption of 5‐hydroxymethylfurfural. In situ electrochemical impedance spectroscopy further shows that CuO/Co3O4 has faster reaction kinetics and lower reaction potential in oxygen evolution reaction and 5‐hydroxymethylfurfural electrocatalytic oxidation. Moreover, CuO/Co3O4 also has a good reduction effect on . The ex‐situ Raman spectroscopy shows that under the reduction potential, the metal oxide is reduced, and the generated Cu2O can be used as a new active site for the reaction to promote the electrocatalytic conversion of to NH3 synthesis. This work provides valuable guidance for the synthesis of value‐added chemicals by 5‐hydroxymethylfurfural electrocatalytic oxidation coupled with while efficiently producing NH3.