Initial Electrode Kinetics of Anion Intercalation and De‐intercalation in Nonaqueous Al‐Graphite Batteries†

Graphitic materials with intercalated sites are considered as the mostly used positive electrode materials in nonaqueous Al batteries. Unlike the small‐size cations, the intercalation/de‐intercalation of large‐size anions into/out of graphite would induce large volume expansion and micro‐structure reconfiguration, leading to unexpected coulombic efficiency in the full cells (<95% within initial several cycles). For understanding the irreversible processes induced by anion intercalation/de‐intercalation (AlCl₄^–), here the kinetics of first two cycles for the Al‐graphite batteries have been systematically studied. To study kinetics behaviors at representative states, a combined method upon galvanostatic intermittent titration technique and electrochemical impedance spectroscopy has been carried out. The achieved diffusion coefficients of the positive electrodes assembled with different graphite sizes suggest that size effect also plays a critical role in determining the electrochemical kinetics in the mass transport in both electrolyte and graphitic layers as well as in interface reaction. The morphologies and micro‐structures of the post‐cycled graphite electrodes have been also experimentally studied, which also well supports the irreversible intercalation/de‐intercalation behaviors in graphite electrodes. The results offer a significant platform to well understand the essential factors in tailoring coulombic efficiency from a kinetic view, which would be helpful in promoting the graphite electrodes in Al batteries.     

2D Covalent Organic Framework for Water Harvesting with Fast Kinetics and Low Regeneration Temperature

Atmospheric water harvesting represents a promising technique to address water stress. Advanced adsorbents have been rationally designed to achieve high water uptake, yet their water sorption kinetics and regeneration temperature greatly limit water production efficiency. Herein, we demonstrated that 2D covalent organic frameworks (COFs), featuring hydrophobic skeleton, proper hydrophilic site density, and 1D open channels significantly lowered the water diffusion and desorption energy barrier. DHTA-Pa COF showed a high water uptake of 0.48 g/g at 30 % R.H. with a remarkable adsorption rate of 0.72 L/Kg/h (298 K) and a desorption rate of 2.58 L/Kg/h (333 K). Moreover, more than 90 % adsorbed water could be released within 20 min at 313 K. This kinetic performance surpassed the reported porous materials and boosted the efficiency for multiple water extraction cycles. It may shed light on the material design strategy to achieve high daily water production with low-energy input.     

In Situ Polymerized 1,3-Dioxolane Electrolyte for Integrated Solid-State Lithium Batteries

Solid-state lithium batteries are promising and safe energy storage devices for mobile electronics and electric vehicles. In this work, we report a facile in situ polymerization of 1,3-dioxolane electrolytes to fabricate integrated solid-state lithium batteries. The in situ polymerization and formation of solid-state dioxolane electrolytes on interconnected carbon nanotubes (CNTs) and active materials is the key to realizing a high-performance battery with excellent interfacial contact among CNTs, active materials and electrolytes. Therefore, the electrodes could be tightly integrated into batteries through the CNTs and electrolyte. Electrons/ions enable full access to active materials in the whole electrode. Electrodes with a low resistance of 4.5 Ω □⁻¹ and high lithium-ion diffusion efficiency of 2.5×10⁻¹¹ cm² s⁻¹ can significantly improve the electrochemical kinetics. Subsequently, the batteries demonstrated high energy density, amazing charge/discharge rate and long cycle life.     

Janus 2D materials via asymmetric molecular functionalization

Janus two-dimensional materials (2DMs) are a novel class of 2DMs in which the two faces of the material are either asymmetrically functionalized or are exposed to a different local environment. The diversity of the properties imparted to the two opposing sides enables the design of new multifunctional materials for applications in a broad variety of fields including opto-electronics, energy storage, and catalysis. In this perspective, we summarize the most enlightening experimental methods for the asymmetric chemical functionalization of 2DMs with tailored made (macro)molecules by means of a supratopic binding (one side) or antaratopic binding (two sides) process. We describe the emergence of unique electrical and optical characteristics resulting from the asymmetric dressing of the two surfaces. Representative examples of Janus 2DMs towards bandgap engineering, enhanced photoresponse and photoluminescence are provided. In addition, examples of Janus 2DMs for real applications such as energy storage (batteries and supercapacitors) and generation (photovoltaics), opto-electronics (field-effect transistors and photodetectors), catalysis, drug delivery, self-healing materials, chemical sensors and selective capture and separation of small molecules are also described. Finally, we discuss the future directions, challenges, and opportunities to expand the frontiers of Janus 2DMs towards technologies with potential impact in environmental science and biomedical applications.

The asymmetric molecular functionalization of two-dimensional materials on one (supratopic) or both (antaratopic) faces enables the design of new multifunctional Janus materials for applications in opto-electronics, energy storage, and catalysis.     

Carbon dioxide capture by aminoalkyl imidazolium-based ionic liquid: a computational investigation

Efficient technologies/processes for CO(2) capture are greatly desired, and ionic liquids are recognized as promising materials for this purpose. However, the mechanisms for selectively capturing CO(2) by ionic liquids are unclear. In this study, the interactions between CO(2) and 1-n-amino-alkyl-3-methyl-imidazolium tetrafluoroborate, an amino imidazolium ionic liquid (AIIL), in its CO(2) capturing process, are elucidated with both quantum chemistry and molecular dynamics approaches on the molecular level. The effects of the straight aminoalkyl chain length in imidazolium-based cations on CO(2) capture are explored, and thereby the factors governing CO(2) capture for this ionic liquid family, e.g., ionic liquid structure, charge distribution, intermolecular interactions, thermodynamic properties and absorption kinetics, are analyzed. Molecular dynamics simulations are used to study the diffusion of the involved compounds and liquid structures of the CO(2)-AIIL systems. The results show that the amino-alkyl chain length plays an important role in governing the absorption properties of AIILs, including the free energies of absorption, equilibrium constants, desorption temperature, absorption rate constants, diffusion coefficients, and organization of CO(2) around cations and anions. This study provides useful information about rational design of ionic liquids for efficient CO(2) capture.     

铁电极电还原溴化钠甲醇溶液反应动力学和机理

研究溴化钠（NaBr）甲醇溶液在铁电极上电还原反应动力学和机理对于二茂铁电化学制备、非水体系中二氧化碳（CO₂）的电还原和有机电合成等领域具有实际价值和科学意义, 但对此未见详细报道. 本文采用极化曲线和电化学阻抗谱等技术详细地研究了该体系的电还原动力学和机理. 结果表明: 反应物为甲醇而Na⁺只起导电作用; 电极电位是该体系中唯一状态变量, 其对甲醇电还原速率常数的影响符合阿仑尼乌斯唯象方程式; 电还原过程不受扩散极化控制, 溶液欧姆极化是主要极化形式; 甲醇电还原依法拉第定律计量地产生氢气, 反应活化能约为26.2 kJ·mol^-1.     

High performance organic thin film transistors with solution processed TTF-TCNQ charge transfer salt as electrodes

Fabrication of high-performance organic thin film transistors (OTFTs) with solution processed organic charge transfer complex (TTF-TCNQ) film as bottom contact source-drain electrodes is reported. A novel capillary based method was used to deposit the source-drain electrodes from solution and to create the channel between the electrodes. Both p- and n-type OTFTs have been fabricated with solution deposited organic charge transfer film as contact electrodes. Comparison of the device performances between OTFTs with TTF-TCNQ as source-drain electrodes and those with Au electrodes (both top and bottom contact) indicate that better results have been obtained in organic complex film contacted OTFT. The high mobility, low threshold voltage, and efficient carrier injection in both types of OTFTs implies the potential use of the TTF-TCNQ based complex material as low-cost contact electrodes. The lower work function of the TTF-TCNQ electrode and better contact of the complex film with the organic thin film owing to the organic-organic interface results in efficient charge transfer into the semiconductor yielding high device performance. The present method having organic metal as contact materials promises great potential for the fabrication of all-organics and plastic electronics devices with high throughput and low-cost processing.     

All-solid-state planar miniature ion-selective chloride electrode

All-solid-state ion-selective electrodes with plastic membrane (poly(vinyl chloride) (PVC), bis(2-ethylhexyl) sebacate (DOS), methyltri-n-tetradecylammonium chloride (MTTACl)), a conducting poly(pyrrole) (PPy) film doped either with chloride ions (PPyCl) or hexacyanoferrate(II) ions (PPyFeCN), and glassy carbon (GC) or screen-printed graphite layer (S-PG) as an inner electric contact were investigated. All the electrodes show close to Nernstian response, but their lifetimes vary. The at least 2-months lifetime of screen-printed electrodes is only achieved for the electrodes containing PPyFeCN (cation-exchanging film). Shorter lifetime of other screen-printed electrodes, i.e. without PPy, or with PPyCl (anion-exchanging film), was attributed to the diffusion of anionic products of the hydrolysis of organic components of the graphite paste used to prepare the electric contact. The properties of miniature, screen-printed electrodes comprising PPyFeCN solid contact, were comparable to those ion-selective electrodes with PPy solid contact (regardless the ion-exchanging characteristic of the polymer) deposited on GC electric contact.     

Molecular Tailoring of p–type Organics for Zinc Batteries with High Energy Density

P-type organic electrode materials are known for their high redox voltages and fast kinetics. However, single-electron p-type organic materials generally exhibit low capacity despite high operating voltage and stability, while some multi-electron p-type organic materials have high theoretical capacity but low stability. To address this challenge, we explore the possibility of combining single-electron and multi-electron units to create high-capacity and stable p-type organic electrodes. We demonstrate the design of a new molecule, 4,4′-(10H-phenothiazine-3,7-diyl) bis (N,N-diphenylaniline) (PTZAN), which is created by coupling the triphenylamine molecule and the phenothiazine molecule. The resulting PTZAN||Zn battery shows excellent stability (2000 cycles), high voltage (1.3 V), high capacity (145 mAh g⁻¹), and energy density of 187.2 Wh kg⁻¹. Theoretical calculations and in/ex situ analysis reveal that the charge storage of the PTZAN electrode is mainly driven by the redox of phenothiazine heterocycles and triphenylamine unit, accompanied by the combination/release of anions and Zn²⁺.     

Mechanical degradation of electrode materials within single particle model in Li-ion batteries for electric vehicles

Mechanical degradation of electrode materials, in the form of particle cracking and fragmentation, disintegration, fracturing, and loss in contact between current collectors and the active electrode materials, can affect or deteriorate the performance of Li-ion batteries dramatically and even lead to the battery failure in electric vehicle. This paper firstly built a single particle model (SPM) based upon kinetics of electrochemical reactions. Then the Li-ion concentration, evolution of diffusion induced stresses within the SPM under potentiostatic or galvanostatic operating conditions were analyzed by utilizing a mathematical method. Next, evolution of stresses or strains in the SPM, at the core of relates with mechanical degradation of electrode materials, are elaborated in detail. Finally, surface and morphology of the electrodes dismantled from fresh and degraded cells after galvanostatic charge/discharge cycling have been analyzed to verify the hypothesis aforementioned by observing scanning electron microscopy and analyzing X-ray diffraction.     

Electrochemistry of TEMPO in the aqueous liquid/vapor interfacial region: measurements of the lateral mobility and kinetics of surface partitioning

A new method is described to simultaneously determine the kinetics of surface partitioning and the lateral diffusion constant of redox active amphiphiles. It concerns water-soluble amphiphiles for which the surface adsorption equilibrium constant and the solution diffusion constant are measured independently. The method involves cyclic voltammetric experiments carried out at the air/water interface with microband electrodes aligned with the plane of the water surface. Typically, 100 nm wide, 1.0 cm long microband electrodes are fabricated by the vacuum vapor deposition of gold films on glass. The front face of the electrode substrates are coated with impermeable, dimensionally stable, polymer barrier films with thickness L in the range of approximately 0.1-1.0 microm. Fracturing such gold-coated glass substrates exposes gold microbands. The recorded voltammetric current sensitively depends on the barrier film thickness, the surfactant surface diffusion constant, Dsurf, and its rate constant of desorption, kdes. For a given surfactant, such as the nitroxyl piperidine free radical TEMPO featured in this report, large currents are observed with microband electrodes that do not carry a barrier film (L = 0). This is because the surfactant surface population diffusing along the air/water interface can be directly electro-oxidized at the edge of the microband. Smaller currents are measured in the presence of a barrier film, since, in those instances, the surface population may contribute to the voltammetric current only via a mechanism involving surfactant desorption from the water surface into bulk, where it contributes to the three-dimensional solution diffusion processes. The quantitative interpretation of the voltammetric experiments was made possible with finite element simulations with FEMLAB. These produce a set of calibration curves, Dsurf versus log kdes, for each value of the barrier film thickness. The intersection of the calibration curves determines the unique values of Dsurf and kdes. For TEMPO, Dsurf = 4.4 +/- 1.2 x 10(-5) cm2/s and kdes >/= 2 x 10(4) s(-1). Surfactant desorption rate constants of this magnitude have not been previously experimentally accessible. Since, in our earlier report (Wu, D. G.; Malec, A. D.; Head-Gordon, M.; Majda, M. J. Am. Chem. Soc. 2005, 27, 4490-4496), we showed that TEMPO is not immersed in water and that it diffuses along the interface hydrogen-bonded to just one or two water molecules, its Dsurf value approximates the water diffusion constant in the aqueous liquid-vapor interfacial region.     

Unraveling the stabilization mechanism of solid electrolyte interface on ZnSe by rGO in sodium ion battery

Transition metal selenides have been widely studied as anode materials of sodium ion batteries(SIBs),however,the investigation of solid-electrolyte-interface(SEI)on these materials,which is critical to the electrochemical performance of SIBs,remains at its infancy.Here in this paper,ZnSe@C nanoparticles were prepared from ZIF-8 and the SEI layers on these electrodes with and without reduced graphene oxide(rGO)layers were examined in details by X-ray photoelectron spectroscopies at varied charged/discharged states.It is observed that fast and complicated electrolyte decomposition reactions on ZnSe@C leads to quite thick SEI film and intercalation of solvated sodium ions through such thick SEI film results in slow ion diffusion kinetics and unstable electrode structure.However,the presence of rGO could efficiently suppress the decomposition of electrolyte,thus thin and stable SEI film was formed.ZnSe@C electrodes wrapped by rGO demonstrates enhanced interfacial charge transfer kinetics and high electrochemical performance,a capacity retention of 96.4%,after 1000 cycles at 5 A/g.This study might offer a simple avenue for the designing high performance anode materials through manipulation of SEI film.     

In situ studies of the adsorption kinetics of 4-nitrobenzenediazonium salt on gold

Self-assembled organic layers are an important tool for modifying surfaces in a range of applications in materials science. Covalent modification of metal surfaces with aryldiazonium cations has attracted much attention primarily because this reaction offers a route for spontaneously grafting a variety of aromatic moieties from solution with high yield. We have investigated the kinetics of this process by performing real-time, in situ nanogravimetric measurements. The spontaneous grafting of 4-nitrobenzene diazonium salts onto gold electrodes was studied via quartz crystal microbalance (QCM) from aqueous solutions of the salt at varying concentrations. The concentration dependence of the grafting rate within the first 10 min is best modeled by assuming a reversible adsorption process with free energy comparable to that reported for arylthiols self-assembled on gold. Multilayer formation was observed after extended grafting times and was found to be favored by increasing bulk concentrations of the diazonium salt. Modified gold surfaces were characterized ex situ with cyclic voltammetry, infrared reflection absorbance spectroscopy, and X-ray photoemission spectroscopy. Based on the experimentally determined free energy of adsorption and on the observed grafting rates, we discuss a proposed mechanism for aryldiazonium chemisorption.     

Electrocatalytic Oxidation of Paracetamol on Ni and NiCu Alloy Modified Glassy Carbon Electrode

In this study we investigated the electrocatalytic oxidation of anti‐inflammatory drug (paracetamol) on Nickel and Nickel–copper alloy modified glassy carbon electrodes (GC/Ni and GC/NiCu) in alkaline solution. These electrodes prepared by galvanostatic method and different electrochemical techniques such as cyclic voltammetry and chronoamperometry were used to track the oxidation process and its kinetics. From Voltammetric studies we concluded that in the presence of drugs the anodic peak current of low valences Nickel species increased, followed by a decrease in the corresponding cathodic current peak. This indicates that drugs were oxidized on the redox mediator which was immobilized on the electrode surface via an electrocatalytic mechanism. Using Laviron's equation, the values of α and k_s for the immobilized redox species were determined. The anodic peak currents show linear dependency with the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of paracetamol was found in agreement with the values obtained from CV measurements.     

Miniature organic transistors with carbon nanotubes as quasi-one-dimensional electrodes

As the dimensions of electronic devices approach those of molecules, the size, geometry, and chemical composition of the contact electrodes play increasingly dominant roles in device functions. It is shown here that single-walled carbon nanotubes (SWNT) can be used as quasi-one-dimensional (1D) electrodes to construct organic field effect transistors (FET) with molecular scale width ( approximately 2 nm) and channel length (1-3 nm). An important feature owing to the quasi-1D electrode geometry is the favorable gate electrostatics that allows for efficient switching of ultra-short organic channels. This affords room temperature conductance modulation by orders of magnitude for organic transistors that are only several molecules in length, with switching characteristics superior to similar devices with lithographically patterned metal electrodes. With nanotubes, covalent carbon-carbon bonds could be utilized to form contacts to molecular materials. The unique geometrical, physical, and chemical properties of carbon nanotube electrodes may lead to various interesting molecular devices.     

Solid-state composite electrolyte LiI/3-hydroxypropionitrile/SiO2 for dye-sensitized solar cells

A new compound, LiI(3-hydroxypropionitrile)(2), is reported here. According to its single-crystal structure (C2/c), this compound has 3-D transporting paths for iodine. Further ab initio calculation shows that the activation energy for diffusion of iodine (0.73 eV) is much lower than that of lithium ion (8.39 eV) within the lattice. Such a mono-ion transport feature is favorable as solid electrolyte to replace conventional volatile organic liquid electrolytes used in dye-sensitized solar cells (DSSC). LiI and 3-hydroxypropionitrile (HPN) can form a series of solid electrolytes. The highest ambient conductivity is 1.4 x 10(-)(3) S/cm achieved for LiI(HPN)(4). However, it tends to form large crystallites and leads to poor filling and contact within porous TiO(2) electrodes in DSSC. Such a drawback can be greatly improved by introducing micrometer-sized and nanosized SiO(2) particles into the solid electrolyte. It is helpful not only in enhancing the conductivity but also in improving the interfacial contact greatly. Consequently, the light-to-electricity conversion efficiency of 5.4% of a DSSC using LiI(HPN)(4)/15 wt % nano-SiO(2) was achieved under AM 1.5 simulated solar light illumination. Due to the low cost, easy fabrication, and relatively high conversion efficiency, the DSSC based on this new solid-state composite electrolyte is promising for practical applications.     

Electrochemical Impedance Analysis of Thermogalvanic Cells

Thermogalvanic cells(also known as thermo-electrochemical cells) that convert waste heat energy to electricity are a new type of energy conversion device. However, the electron transfer kinetics and mass transfer of redox couples have not been thoroughly studied. Here, the ion reaction and charge transport in thermogalvanic cells are investigated by electrochemical impedance analysis. We first propose the detailed impedance model followed experimental verification on three types of electrode materials. Parameters including kinetic rate constants and ion diffusion coefficients for the electrodes are obtained by fitting the impedance data. Our study shows explicitly that impedance analysis can provide useful information on selecting suitable electrode materials for thermogalvanic cells.     

Impact of metal cations on the electrocatalytic properties of Pt/C nanoparticles at multiple phase interfaces

Proton-exchange membrane fuel cells (PEMFCs) use carbon-supported nanoparticles based on platinum and its alloys to accelerate the rate of the sluggish oxygen-reduction reaction (ORR). The most common metals alloyed to Pt include Co, Ni and Cu, and are thermodynamically unstable in the PEMFC environment. Their dissolution yields the formation and redistribution of metal cations (M(y+)) within the membrane electrode assembly (MEA). Metal cations can also contaminate the MEA when metallic bipolar plates are used as current collectors. In each case, the electrical performance of the PEMFC severely decreases, an effect that is commonly attributed to the poisoning of the sulfonic acid groups of the perfluorosulfonated membrane (PEM) and the resulting decrease of the proton transport properties. However, the impact of metal cations on the kinetics of electrochemical reactions involving adsorption/desorption and bond-breaking processes remains poorly understood. In this paper, we use model electrodes to highlight the effect of metal cations on Pt/C nanoparticles coated or not with a perfluorosulfonated ionomer for the CO electrooxidation reaction and the oxygen reduction reaction. We show that metal cations negatively impact the ORR kinetics and the mass-transport resistance of molecular oxygen. However, the specific adsorption of sulfonate groups of the Nafion? ionomer locally modifies the double layer structure and increases the tolerance to metal cations, even in the presence of sulphate ions in the electrolyte. The survey is extended by using an ultramicroelectrode with cavity and a solid state cell (SSC) specifically developed for this study.     

Mechanism of Cations Suppressing Proton Diffusion Kinetics for Electrocatalysis

Proton transfer is crucial for electrocatalysis. Accumulating cations at electrochemical interfaces can alter the proton transfer rate and then tune electrocatalytic performance. However, the mechanism for regulating proton transfer remains ambiguous. Here, we quantify the cation effect on proton diffusion in solution by hydrogen evolution on microelectrodes, revealing the rate can be suppressed by more than 10 times. Different from the prevalent opinions that proton transport is slowed down by modified electric field, we found water structure imposes a more evident effect on kinetics. FTIR test and path integral molecular dynamics simulation indicate that proton prefers to wander within the hydration shell of cations rather than to hop rapidly along water wires. Low connectivity of water networks disrupted by cations corrupts the fast-moving path in bulk water. This study highlights the promising way for regulating proton kinetics via a modified water structure.     

Interfacial properties of precipitate-based ion-selective electrodes : Rotating disk impedance measurements of the Ag2S/Ag (aqueous) interface

Three-electrode rotating disk impedance measurements were made from 31.6 kHz to 0.0178 Hz on Ag₂S/Ag⁺ (aqueous) and Ag₂S/Ag systems. Membranes were prepared from materials precipitated in excess of silver or sulfide ions, and stoichiometric mixtures. Impedances were analyzed, as a function of rotation rate and bathing activities, to isolate bulk conductivities, internal diffusion, surface kinetic and dissolution/crystallization impedances. High-frequency bulk resistivities, R_∞, varied by four with precipitation and pressing conditions. Resistivities were the same for solution and ohmic configurations for each preparation. For ohmic contacts, R_∞ and R(DC) were identical. Solution contact cells in 10^-1 M and 10^-2 M bathing silver ion solution gave identical frequency-dependent impedances which were independent of rotation rate. Thus, solution diffusional impedances and solution dependent surface kinetics were eliminated, and a finite Warburg, interior-Ag⁺-defect, diffusion impedance was indicated. Summation of bulk membrane and contact resistances, and this Warburg impedance served as a 'background' correction in analyzing dilute bathing solution interfacial impedances for surface effects. Corrected impedances in 10^-3 –10^-5 M AgNO₃ showed solution diffusional behaviour combined with surface kinetic and dissolution impedances. An iterative linear least-squares method resolved these quantities. The surface resistance suggests a potential-dependent rate constant; dissolution time constants were solution-independent and smaller than those for solution diffusion. Thus, dissolution can be a rate-limiting step in establishment of steady-state potentials.