Interfacial Transfer Kinetics Research Articles

Mechanistic Insights into Surfactant-Modulated Electrode-Electrolyte Interface for Steering H2O2 Electrosynthesis.

Electrocatalytic reactions taking place at the electrified electrode-electrolyte interface involve processes of proton-coupled electron transfer. Interfacial protons are delivered to the electrode surface via a H2O-dominated hydrogen-bond network. Less efforts are made to regulate the interfacial proton transfer from the perspective of interfacial hydrogen-bond network. Here, we present quaternary ammonium salt cationic surfactants as electrolyte additives for enhancing the H2O2 selectivity of the oxygen reduction reaction (ORR). Through in situ vibrational spectroscopy and molecular dynamics calculation, it is revealed that the surfactants are irreversibly adsorbed on the electrode surface in response to a given bias potential range, leading to the weakening of the interfacial hydrogen-bond network. This decreases interfacial proton transfer kinetics, particularly at high bias potentials, thus suppressing the 4-electron ORR pathway and achieving a highly selective 2-electron pathway toward H2O2. These results highlight the opportunity for steering H2O-involved electrochemical reactions via modulating the interfacial hydrogen-bond network.

Fluorinated carbon encapsulated NiO cluster/TiO2 nanotubes as a robust photocatalyst for hydrogen evolution

Theoretical predictions directed modulations on work function, kinetics of interfacial charge transfer and surface hydrogen binding from NiO cluster and highly electronegative surface encapsulation allow significant increases in HER performance.

Cyclic Voltammetry to Study Dynamics of Ion Insertion in Porous Materials

Electrochemical charge storage in porous materials is associated with ion adsorption at the meso/nanopores surface (physical insertion) and/or insertion in the bulk material (chemical insertion). The first process is capacitive whereas the second is Faradaic. A model is brought about for describing the cyclic voltammetry responses of these systems and their dependence upon the various intrinsic and operational governing parameters. These responses may be considered as illustrating the behaviors expected in working conditions in terms of diagnosis of the main phenomena at work and of their mutual interactions, namely, dynamics of double‐layer charging, transport in solution, transport in the pores, interfacial transfer kinetics, and transport in the material bulk. Several limiting cases are examined in details and discussed, focusing on the effect of scan rate as a widely used diagnostic tool.

Construction of an ultra-stable mixed conductive layer to stabilize the solid-state electrolyte/Na interface by in-situ interface chemistry

The quest for high energy density, essentially safe, and cost-effective energy storing systems is powering the evolution of solid-state sodium metal batteries (SSSMBs). However, insufficient Na/solid-state electrolyte (SSE) interface contact leads to the formation of sodium dendrites, causing premature cell failure and safety issues that limit their practical application. Here, a novel ultra-stable mixed conductive layer (MCL) composed of Na15Sn4 and NaF is introduced at the Na|Na3Zr2Si2PO12 (NZSP) interface through in-situ interface chemistry. Such an MCL not only enables the transformation of the NZSP surface from sodiophobic to sodiophilic to achieve intimate contact with Na but also homogenizes the Na+ flux without dendritic sodium. Benefiting from the construction of the multifunctional interface, a high critical current density (CCD) of 1.3 mA cm−2 and an exceptionally long cycle life of 6000 h at 0.3 mA cm−2 are achieved for the Na|SnF2@NZSP|Na cell at room temperature (RT). Furthermore, the Na|SnF2@NZSP|Na3V2(PO4)3 full cell shows excellent cycling performance (91 % of maintained capacity for over 500 cycles at 1 C) and rate capability (101.4 mAh/g at 5 C) at RT. This work presents a validated method for the coordinated regulation of interfacial transfer kinetics and inhibition of sodium dendrite growth.

Diffusion-Reaction-Deformation Coupled Modeling of Large-Deformed Germanium Thin Film Anodes

Germanium is known as a high-capacity material that reversibly stores large amounts of lithium, whereas the inevitable volume changes lead to mechanical failures and unstable reaction interfaces. According to the finite deformation theory, we establish a theoretical framework to capture the viscoplastic flow and the interfacial transfer kinetics during lithiation and delithiation under coupled diffusion-reaction-deformation environments. Many microcracks on the surface of germanium electrodes are observed by previous experiments, and we take this effect into consideration by associating the parameters of Li-Ge alloy with the degree of lithiation, such as the concentration-dependent elasticity modulus and yield stress. Subsequently, the framework is used to calculate the mechanical and electrochemical response of thin film electrodes during charge and discharge under the rigid substrate constraint. The results suggest that charge rate and electrode thickness determine the performance of thin film battery, which is in accordance with the experimentally observed phenomenon. The Cauchy stress in the thin film electrode is also subject to the effect of the inhomogeneous spatial distribution of stress, and the stress drop at the ends of the electrodes is the main source of material fracture failure.

Scanning Electrochemical Microscope Studies of Charge Transfer Kinetics at the Interface of the Perovskite/Hole Transport Layer

Interfacial carrier transfer kinetics is critical to the efficiency and stability of perovskite solar cells. Herein, we measure the regeneration rate constant, absorption cross-section, reduction rate constant, and conductivity of hole transport layered perovskites using scanning electrochemical microscopy (SECM). The SECM feedback revealed that the regeneration rate constant, absorption cross-section, and reduction rate constant of the nickel oxide (NiO) layer perovskite layer are higher than those of the poly (3,4-ethyenedioxythiophene)-poly (styrenesulfonate) layered perovskite. Also, at a specific flux density ( J h v ), the value of the regeneration rate constant (keff) in both blue and red illuminations for the NiO/CH3NH3PbI3 film is significantly higher than in both PEDOT: PSS/CH3NH3PbI3 and FTO/CH3NH3PbI3 films. The difference in keff between layered and nonlayered perovskite conforms to the impact of the hole conducting layer on the charge transfer kinetics. According to the findings, SECM is a powerful approach for screening an appropriate hole transport layer for stable perovskite solar cells.

Accelerating solid-liquid interfacial hole transfer kinetics through designed flower-like trivalent bismuth crystallite island for photoelectrochemical application

Hematite (Fe2O3) is an appealing photoanode material for photoelectrochemical application due to its suitable band-gap. However, the serious electron-hole recombination of hematite results in the photocurrent density generated is lower than the theoretical value. In this work, we loaded flower-like trivalent bismuth crystallite islands onto nano Fe2O3 electrodes to improve photoelectrochemical application. The trivalent bismuth ions decorated hematite photoanode demonstrates excellent photocurrent density, rapid water oxidation kinetics, and remarkable bulk separation efficiency. Mott-Schottky results indicate that surface-treated hematite showed increased carrier density and enhanced uptrend band bending. Furthermore, the trivalent bismuth ions accelerate hole capture through Bi(III)/Bi(V) exchange, reducing the recombination of oxygen-related holes with surface trapping sites. Under simulated sunlight irradiation, the photocurrent density at 1.23 (vs. RHE) exhibits fourfold enhancement that of hematite film. This work demonstrates a new possibility that Bi(III) compounds, in a passivation-like form, can effectively improve carrier transport on the surface of hematite photoanodes.

A Silica-Reinforced Composite Electrolyte with Greatly Enhanced Interfacial Lithium-Ion Transfer Kinetics for High-Performance Lithium Metal Batteries.

Developing quasi-solid-state electrolytes with superior ionic conductivity and high mechanical strength is urgently desired to improve the safety and cycling stability of lithium-metal batteries. Herein, a novel solid-like electrolyte (SLE) with enhanced Li+ interfacial transfer kinetics is rationally designed by soaking bulk nanostructured silica-polymer composites in liquid electrolytes. Benefiting from the high content of inorganic silica and abundant interfaces for fast Li+ -transport channels, the prepared SLE exhibits superb ionic conductivity and high mechanical strength. Furthermore, fumed silica with a high specific area in the SLE can homogenize Li+ flux and electrical field gradient. More importantly, a Li2 S-rich solid electrolyte interphase (SEI) is constructed on the lithium metal due to the intimate ion coordination in the SLE. Therefore, the lithium-metal anode exhibits excellent electrochemical performance in symmetric Li-Li cells due to the merits of superior ionic conductivity, high modulus, Li2 S-rich SEI, as well as the homogeneous Li+ flux. Full cells with LiFePO4 cathode can still displaya capacity retention of 98% at 0.2 C after 400 cycles. The proposed strategy on quasi-solid-state electrolytes provides a promising avenue for next-generation metal-based batteries.

In Situ Integrating Highly Ionic Conductive LDH‐Array@PVA Gel Electrolyte and MXene/Zn Anode for Dendrite‐Free High‐Performance Flexible Zn–Air Batteries

AbstractLow interfacial ion transfer kinetics and structure instability of solid‐state electrolytes are the bottleneck which seriously limits the working life and energy density of flexible zinc–air batteries (ZABs). Herein, an optimized electrode–electrolyte integrated MXene/Zn‐layered double hydroxides (LDH)‐array@PVA structure is developed via an electrochemical Zn deposition, in situ LDH growth, polymer infiltration, and crosslinking route, integrating anode and gel polymer electrolyte (GPE) for high‐performance flexible ZABs. The highly orientated hydrophilic CoNi‐LDH arrays sufficiently crosslink with poly(vinyl alcohol) (PVA) chains, which effectively decreases the crystallinity degree of the PVA polymer and provides fast ionic diffusion channels to reduce the ionic transport barrier, endowing LDH‐array@PVA GPE with significantly improved ionic conductivity, water retention capability, and mechanical flexibility. Moreover, the optimized anode‐GPE integrated interface of MXene/Zn‐LDH‐array@PVA demonstrates excellent interfacial compatibility and stability, effectively reduces the interfacial impedance, and promotes the interfacial ionic transfer kinetics, enhancing a uniform zinc deposition without dendrite formation. The optimized ionic transfer kinetics and stable anode‐GPE integrated interface bring the MXene/Zn‐LDH‐array@PVA‐based flexible ZAB a long cycling life up to 50 h, and a high power density of 92.3 mW cm−2. The rationally designed in situ crosslinking and integration strategies provide enlightening pathways for the design of high‐performance flexible ZABs.

Reversible Al Metal Anodes Enabled by Amorphization for Aqueous Aluminum Batteries.

Aqueous aluminum metal batteries (AMBs) are regarded as one of the most sustainable energy storage systems among post-lithium-ion candidates, which is attributable to their highest theoretical volumetric capacity, inherent safe operation, and low cost. Yet, the development of aqueous AMBs is plagued by the incapable aluminum plating in an aqueous solution and severe parasitic reactions, which results in the limited discharge voltage, thus making the development of aqueous AMBs unsuccessful so far. Here, we demonstrate that amorphization is an effective strategy to tackle these critical issues of a metallic Al anode by shifting the reduction potential for Al deposition. The amorphous aluminum (a-Al) interfacial layer is triggered by an in situ lithium-ion alloying/dealloying process on a metallic Al substrate with low strength. Unveiled by experimental and theoretical investigations, the amorphous structure greatly lowers the Al nucleation energy barrier, which forces the Al deposition competitive to the electron-stealing hydrogen evolution reaction (HER). Simultaneously, the inhibited HER mitigates the passivation, promoting interfacial ion transfer kinetics and enabling steady aluminum plating/stripping for 800 h in the symmetric cell. The resultant multiple full cells using Al@a-Al anodes deliver approximately a 0.6 V increase in the discharge voltage plateau compared to that of bare Al-based cells, which far outperform all reported aqueous AMBs. In both symmetric cells and full cells, the excellent electrochemical performances are achieved in a noncorrosive, low-cost, and fluorine-free Al2(SO4)3 electrolyte, which is ecofriendly and can be easily adapted for sustainable large-scale applications. This work brings an intriguing picture of the design of metallic anodes for reversible and high-voltage AMBs.

Constructing Defect-Mediated CdS/g-C3N4 by an In-situ interlocking strategy for Cocatalyst-free photocatalytic H2 production

The construction of heterojunction photocatalyst is an emerging strategy for realizing efficient photocatalytic hydrogen production, and the methodology of construction is critical for improving the interfacial charge carriers separation and transfer. A weakly coupling interface in a heterojunction leads to lower hydrogen production activity and stability. Herein, a facile strategy based on an in-situ interlocking reaction is developed to solve the interfacial contact issue. Litchi-like CdS is anchored at the defects of the g-C3N4 (CN) by an interlocking process, and the contact interface is further extended by some small necking CdS particles that assembled on the contact corner because of the surface tension. The as-formed CdS/g-C3N4 (CdS/CN) has a unique and strongly coupling interface, which can effectively improve interfacial separation and transfer kinetics of photogenerated charge carriers due to the synthetic advantages of interlocking binding, necking effect, and heterojunction. Impressively, the as-prepared CdS/CN photocatalyst yields over 36 folds of cocatalyst-free hydrogen generation rate than the pure CdS under the visible light irradiation. This work presents a case of practical study to realize the synthesis of defect-mediated heterojunction photocatalysts by a facile strategy.

Interface evolution and performance degradation in LiCoO2 composite battery electrodes monitored by advanced EQCM

Unravelling the underlying reasons for degradation mechanism of battery materials is of great fundamental and practical importance. For a classical electrode consisting of an active material, a conductive additive, and a polymeric binder, its capacity fading is commonly related with (i) mechanical degradation of polymeric binder and/or (ii) structural and compositional degradation of active materials. The former is more relevant for electrodes showing volume expansion and represented by the progressive breakage of polymeric binder network during battery operation, leading to the dissolution of the other two components into electrolytes. The latter is generally reflected by an irreversible phase transition in active materials, which may affect the species exchanged at the electrode/electrolyte interface and their interfacial transfer dynamics. By employing a coupled methodology pairing electrochemical techniques with piezoelectric probes derived from quartz crystal microbalance (QCM), this work reports on the evolution of the interfacial processes during electrochemical cycling and correlates to the performance degradation of the electrodes. Shown on a LiCoO2 (LCO) composite electrode as a model system, it was revealed that bare Li+ without a hydration sheath plays a dominant role in charge balance irrespective of the aging degree of the electrode under the experimental conditions of this work. However, Li+ transfer is closely accompanied with free H2O molecules with a Li+:H2O ratio around 10:1 at a polarization state close to LCO redox potential (0.65 V vs. Ag/AgCl). This ratio persists in all cycled electrodes with gradually faded interfacial transfer kinetics of Li+ and H2O along cycling. Such fading in species interfacial transfer kinetics driven by the surficial evolution from LiCoO2 to CoO plays a major role in the electrode performance degradation during cycling.

Kinetics of Interfacial Ion Transfer in Lithium-Ion Batteries: Mechanism Understanding and Improvement Strategies.

The development of high-rate lithium-ion batteries is required for automobile applications. To this end, internal resistances must be reduced, among which Li+ transfer resistance at electrode/electrolyte interfaces is known to be the largest. Hence, it is of urgent significance to understand the mechanism and kinetics of the interfacial Li+ transfer. This Spotlight on Applications presents recent progress in the analysis and mechanical understanding of interfacial Li+ transfer. First, we review the reported activation energies (Ea) at various solid/liquid interfaces. On this basis, the mechanism and rate-determining step of the interfacial Li+ transfer are discussed from the viewpoints of the desolvation of Li+, the nature of the solid electrolyte interphase (SEI), and the surface structural features of electrodes. After that, we introduce promising strategies to reduce the Ea, highlighting some specific cases that give remarkably low Ea. We also note the variations in frequency factors or pre-exponential factors (A) of the interfacial Li+ transfer, which are primarily dominated by the number of Li+ intercalation sites on electrode surfaces. The current understanding and improvement strategies of interfacial Li+ transfer kinetics presented herein will be a foundation for designing high-rate lithium-ion batteries.

Surface states modulation of hematite photoanodes for enhancing photoelectrochemical catalysis

Sluggish interfacial carrier transfer and oxygen production kinetics of photoelectrochemical water splitting are related to the Fermi-level pinning of the hematite surface states, thus it requires extra energy input and results in low PEC efficiency. Here we develop a facile secondary calcination strategy for regulating the density and distribution of surface states in hematite photoanode system. The fabricated α-Fe2O3-450 possesses significantly reduced disordered layers and renovated surface oxygen vacancy structure to increase carrier density and effectively passivate surface trapping states. Thus, both bulk and interfacial recombination of electrons and holes are effectively suppressed, and the quasi-hole Fermi level moves to more positive position, leading to a large photovoltage for reducing kinetic overpotential. Therefore, the photocurrent density of α-Fe2O3-450 (1.035 mA cm−2) is 1.8 times higher than that of pristine α-Fe2O3 (0.58 mA cm−2) at 1.23 V versus reversible hydrogen electrode, and α-Fe2O3-450 has more cathodic onset potential than α-Fe2O3.

In Situ Probing Liquid/Liquid Interfacial Kinetics through Single Nanodroplet Electrochemistry.

In this study, we report the new application of single nanodroplet electrochemistry to in situ monitor the interfacial transfer kinetics of electroactive species across liquid/liquid interface. Interfacial kinetic information is crucial in drug delivery and membrane transport. However, interfacial information has been mainly studied thermodynamically, such as partition coefficient, which could not manifest a speed of transfer. Herein, we measure the phase-transfer kinetic constant via the steady-state electrochemistry of an extracted redox species in a single nanodroplet. The redox species were transferred from the continuous oil phase to the water nanodroplet by partition equilibrium. The transferred redox species are selectively electrolyzed within the droplet when the droplet contacts with an ultramicroelectrode, while the electrochemical reaction of the redox species outside the droplet (i.e., organic solvent) is effectively suppressed by adjusting the electrolyte composition. The redox species in the water droplets can quickly attain a steady state during electrolysis owing to an extensive mass transfer by radial diffusion, and the steady-state current can be analyzed to obtain kinetic information with help from the finite-element method. Finally, a quick calculation method is suggested to estimate the kinetic constant of phase transfer without simulation.

Enhanced photovoltaic performance of dye-sanitized solar cell with tin doped titanium dioxide as photoanode materials

Tin doped TiO2 (Sn-TiO2) nanoparticles were synthesized using a simple photolysis method and X-ray diffraction (XRD) studies confirm that they have a 4.59 nm crystallite size and crystallized as an anatase phase of TiO2. Field emission-scanning electron microscope (FE-SEM) and transmission electron microscopy (TEM) reveals the formation of spherical and fusiform agglomeration nanoparticles with mesoporous structure and size equal 20nm approximately. The preparation of 5%Sn:TiO2 is confirmed by energy dispersive X-ray (EDX), and the empirical formal is Sn0.05TiO4. X-ray photoelectron spectroscopy (XPS) revealed that 1% Sn was successfully doped with anatase TiO2 and that Ti+3 was present as an electron trap. Raman spectrum shows a red shift of anatase peaks with doping Sn:TiO2. The adsorption spectrum of Sn doped TiO2 has an excellent transmittance with increasing Sn doping until 5% mole ratio and reaching 85%, as well as decreasing the band gap with increasing Sn doping ratio and reaching a minimum value of 2.62eV corresponding to 5% Sn:TiO2. The results obtained that the optimum conditions for working Sn:TiO2 as a DSSCs are 5%Sn doping ratio, N3 dye solution and pH = 3. EIS measurements were used to quantify the kinetics of interfacial charge transfer, such as chemical capacitance, electron recombination lifespan, charge transfer resistance, charge collection efficiency, and charge transfer resistance. Enhanced power conversion equals 12.32% for %5Sn:TiO2/based N3 dye/GO at pH =3 by using solar simulator (100 mW/cm2 ).

Deposition of zinc cobaltite nanoparticles onto bismuth vanadate for enhanced photoelectrochemical water splitting

During the past few decades, photoelectrochemical (PEC) water splitting has attracted significant attention because of the reduced production cost of hydrogen obtained by utilizing solar energy. Significant efforts have been invested by the scientific community to produce stable ternary metal oxide semiconductors, which can enhance the stability and increase the overall production of oxygen. Herein, we present the ternary metal oxide deposition of ZnCo2O4 as a route to obtain a novel photocatalyst layer on BiVO4 to form BiVO4/ZnCo2O4 a novel composite photoanode for PEC water splitting. The structural, topographical, and optical analyses were performed using field emission scanning electron microscopy, X-ray diffraction, high-resolution transmission electron microscopy, and UV–Vis spectroscopy to confirm the structure of the ZnCo2O4 grafted over BiVO4. A remarkable 4.4-fold enhancement of the photocurrent was observed for the BiVO4/ZnCo2O4 composite compared with bare BiVO4 under visible illumination. The optimum loading of ZnCo2O4 over BiVO4 yields unprecedented stable photocurrent density with an apparent cathodic shift of 0.46 V under 1.5 AM simulated light illumination. This is also evidenced by the flat-band potential change through Mott–Schottky analysis, which reveals the formation of p-ZnCo2O4 on n-BiVO4. The improvement in the PEC performance of the composite with respect to bare BiVO4 is ascribed to the formation of thin passivating layer of p-ZnCo2O4 on n-BiVO4 which improves the kinetics of interfacial charge transfer. Based on our study, we have gained an in-depth understanding of the BiVO4/ZnCo2O4 composite as high potential in efficient PEC water splitting devices.

Numerical modeling of reactive bubbly flows based on Euler-Lagrange approach

In this paper, the Euler-Lagrange approach was employed to simulate the gas–liquid reaction system in a rectangular bubble column by combining hydrodynamics, interfacial mass transfer and reaction kinetics. According to the satisfactory agreement with the experiment results, the detailed characteristics of the hydrodynamics were accurately reflected. For the chemisorption process of CO2 in aqueous NaOH, the results were more similar to the experimental values than those reported in the literature. Moreover, further improvements were successfully implemented: A visible inflection point, owing to which the shape of the curve was highly consistent with the experimental data, could be easily observed when taking into account the auto-dissociation of water. A relatively exact slope for the distribution curve of the mean Sauter diameter could be attained in the flow region below z/H = 0.3. In addition, an in-depth assessment was performed by comparing a series of typical mass transfer and enhancement factor models.

Scrutiny of the LiCoO2 Composite Electrode/Electrolyte Interface by Advanced Electrogravimetry and Implications for Aqueous Li-Ion Batteries

The recent tendency in the battery field toward the use of aqueous electrolytes stimulated several studies searching for compatible electrode materials and charge carriers. Still, another aspect to forge ahead is the fundamental understanding of interfacial processes occurring at electrode/electrolyte interface. To this end, we investigated interfacial properties of a model LiCoO2 composite electrode in Li2SO4 aqueous electrolyte through extensively exploiting operando electrochemical quartz crystal microbalance (EQCM) and its coupling with electrochemical impedance spectroscopy (ac-electrogravimetry). EQCM revealed a global cation-exchange behavior, which is decoded by ac-electrogravimetry into multispecies contribution with different proportions/kinetics, benefiting from the capacity of the latter to study interfacial dynamics. Li+ plays the major role in the charge-compensation mechanism, but a strong interaction with H2O has been revealed with close interfacial transfer kinetics, which provides experimental evidence on the essential character of H2O assisting the Li+ insertion in layered materials due to the weakened charge density by screening the electrostatic interactions between the Li+ ions and the host lattice of cathode materials.

Investigation of interfacial charge transfer kinetics of photocharged Co-Bi modified BiVO4 using scanning electrochemical microscopy (SECM)

Bismuth vanadate (BiVO4) is a promising photoanode for photoelectrochemical (PEC) water oxidation process. However, fast charge recombination and sluggish surface kinetics limit its application. Here, we demonstrate improvement in the PEC performance due to cobalt borate (Co-Bi) incorporation in BiVO4 and due to prolonged exposure in 1 sun illumination. Photocurrent is improved from 0.96 mAcm−2 to 1.95 mAcm−2 at 0.8 V upon Co-Bi incorporation, which plays as a hole collector and hole reservoir. Photocharging treatment leads to further improvements in the photocurrent from 0.96 mAcm−2 to 1.31 mAcm−2 and 1.95 mA cm−2 to 2.63 mAcm−2 for BV and BV/Co-Bi-3 respectively. The scanning electrochemical microscope (SECM) study reveals the improvement in the interfacial hole transfer kinetics from 7.23 × 10−3 to 9.05 × 10−3 cm s−1 and 9.61 × 10−3 to 11.76 × 10−3 cm s−1 for BV and BV/Co-Bi -3, respectively, upon photocharging. The SECM mapping of the interface reflects the localized photoelectrochemical activity of photoanodes. The improvements in the feedback photocurrents upon the Co-Bi incorporation confirm the improved interfacial charge transfer kinetics. Photocharging leads to further improve in the photocurrent for BV and BV/Co-Bi.