H2V3O8 (denoted as HVO) is introduced to achieve high reversible capacity for aqueous zinc-ion batteries, and we investigate the fundamental charge-storage mechanism. Given the importance of the proton-associated reaction, the crystalline K2V3O8 is ion exchanged in HCl aqueous solution to yield HVO nanowires. These nano-wires ultimately result in an open porosity, thereby promoting the electrochemical reaction with protons by shortening the ion/electron transport pathways and reducing both the charge-transfer resistance and activation barrier. Comprehensive analyses indicate that the charge-storage process is governed by a reversible de/protonation reaction rather than conventional Zn2+ intercalation. Notably, the HVO electrode delivers a reversible capacity of 467 mAh g-1 at 0.1 A g-1 and retains 96% of its initial capacity over 900 cycles at 1.5 A g-1, resulting in superior specific capacity, rate capability, and cyclability, which are attributed to the selected nanostructure. Operando and ex situ characterization confirm the formation and reversibility of intermediate phases such as zinc hydroxytriflate and vanadium oxides. The observed pH evolution during cycling further validates the key role of H+ in enabling fast charge storage. This acid-engineered amorphous HVO thus demonstrates clear viability as a practical cathode for aqueous zinc-ion batteries.

Zinc manganite spinel powder specific surface area was found to increase by an order of magnitude via a treatment with sulfuric acid. The specific surface area, determined by nitrogen adsorption, correlates with the specific capacity of zinc manganite spinel positive electrodes. Zinc manganite spinel subjected to a controllable acidic treatment is a promising material for the non-aqueous zinc-ion batteries.

A layer-by-layer approach in the assembly of nanomaterials from the atomic layers electrochemically generated by underpotential deposition was reinforced by the development of the method of multiparametric monitoring of surface-restricted electrochemical reactions based on frequency response analysis under nonstationary conditions. The upd in a wide meaning of this term is not restricted to deposition of a monolayer of one metal onto an electrode of different metal but involves also nonmetals, such as Se and Te, their compounds (CdSe, CdTe, CdS, PbTe, PbSe, Bi2Te3, etc.) and superlattices, such as (Bi2)m(Bi2Te3)n. The experience acquired in the electrochemistry of the underpotential deposition and multilayer assembly can be also helpful in other fields of materials science, such as supercapacitor research, where the frequency response examination of the surface-restricted reactions enables the discrimination between capacitive and noncapacitive currents under conditions preventing from the use of classical impedance spectroscopy and evaluation of energy dissipation in the charge–discharge processes.

Effects of MnO2 electrodeposition on α, β, γ, and δ-MnO2 polymorphs from aqueous zinc sulfate solution with manganese sulfate additive (zinc-ion battery (ZIB) electrolyte) have been examined by cyclic voltammetry, electrochemical impedance spectroscopy, X-ray diffraction, and scanning electron microscopy. Even three cycles of anodic charge and cathodic discharge in the typical potential range used in zinc-ion battery research are sufficient for entire electrode surface coverage by essentially X-ray amorphous deposit with a minor contribution of γ-MnO2. The fast MnO2 deposition proceeds via Mn2+ anodic oxidation upon charge at potentials above 1.8 V (vs. Zn2+/Zn). As a consequence of the fast electrodeposition, the choice of MnO2 polymorph for the positive electrode in aqueous ZIB with Mn(II) additive in the electrolyte turns to be even less critical than in ZIB without Mn(II) additive. Though using a narrower potential range in the battery charging may help to mitigate the MnO2 electrodeposition, the cost of the mitigation would be a reduction of an enhanced capacity of Mn(II)-containing ZIB, as the latter is essentially due to MnO2 anodic deposition.

We introduce an unexpected finding of the de/protonation associated conversion reaction occurred in K2V3O8 as a promising cathode material for zinc-ion batteries. The structure undergoes a conversion reaction between amorphous V5+2O5 and V3+OOH upon cycling when a cut-off voltage up to 1.9 V is applied. A combination of operando X-ray diffraction, in situ Raman spectroscopy, X-ray photoelectron spectroscopy, time-of-flight secondary-ion mass spectroscopy, and operando pH measurement analyses reveal that the reaction of the proton (H+) is indispensable for progression of the conversion reaction. The conversion reaction results in a large reversible capacity of 362 mAh g−1 (~97 % of theoretical capacity) at 0.1 C (37 mA g−1) on discharge and an activity even at a rate of 7 C (187 mAh g−1), with the two-electron reaction by the V5+/3+ redox pair evidenced by operando X-ray absorption spectroscopy analysis. These findings underscore the importance of conversion reversibility associated with the proton reaction for a high cut-off voltage, contributing additional capacity to reach the theoretical capacity for cathode materials of zinc-ion batteries in mildly acidic aqueous systems.

Herein, we investigate the phase evolution and reactions of vanadium hexacyanoferrate (VHCF) cathode in aqueous Zn-ion battery. X-ray diffraction, in situ Raman spectroscopy, scanning electron microscopy, time-offlight secondary-ion mass spectrometry, and electrochemical methods reveal electrochemical activation of VHCF electrode in multiple charge-discharge cycles that eventually converts VHCF into zinc hexacyanoferrate and vanadium oxides (VOx). The emerging VOx redox behavior enhances the specific capacity of the electrode from 77 to 165 mAh g-1. Operando UV-vis absorption spectra of the electrolyte in the vicinity of the electrode during electrochemical reaction verifies the presence of decavanadate anion - the intermediate of VHCF transformation into the electrochemically active vanadium oxide. Analysis of the electrodes under various electrochemical conditions and experiments in aqueous and non-aqueous media demonstrate that vanadium of VHCF is redox inactive in the pristine material but products of VHCF transformation start to contribute to the specific capacity of the electrode upon the formation of vanadium oxide.

Bismuth oxysulfide (BOS) films were formed on dielectric glass substrates by the chemical bath deposition. They have a high sensitivity to moisture content and demonstrate the decrease in the electrical resistance up to three orders of magnitude when the relative humidity reaches 85% and more. The high sensitivity of resistive structure representing 0.65 & mu;m thick film between two Ag contacts is associated with randomly oriented thin nanoplate crystals. The presence of a great number of intergrain boundaries restricts electron transport (both in the dark and under illumination), which is desirable for resistive humidity sensors. The BOS films possess a high surface-to-volume ratio making them ultra-sensitive to adsorption of water. It is supposed that ionic conductivity in a thin layer of adsorbed water plays a crucial role in fast response of sensing structure (1-3 s) to adsorption-desorption cycles. High dark resistance and low photoconductivity of BOS films make them practically insensitive to processes of molecular oxygen adsorption and action of light when they are used as humidity sensing structure.

Strong room temperature exciton photoluminescence (PL) has been observed in copper (I) oxide films electrochemically deposited in a tartrate electrolyte. The PL intensity of these films is two orders of magnitude higher than that of films deposited from the classical lactate electrolyte. X-ray diffraction (XRD) and Raman spectroscopy analyses demonstrate that the films prepared using tartrate electrolyte are characterized by higher grain size, which reduces a non-radiative recombination of charge carriers. Better optical quality of the Cu2O films prepared using tartrate electrolyte is explained taking into account stronger tartrate-copper complexes, which results in lower density of grain boundaries in such films. Moreover, higher buffering capacity of the tartrate complex provides stability of pH value in the diffusion layer of the near-electrode space preventing defect formation. Our study demonstrates the promise of using Cu2O films deposited from tartrate solution for solar energy applications like photoelectric energy conversion, hydrogen production, and photocatalysis.

In this work, different MnO2 polymorphs are applied as cathodes in zinc-ion batteries (ZIBs). All the polymorphs result in similar electrochemical behavior in weak acidic (1 М) ZnSO4 aqueous solutions at comparable specific capacity (200–225 mAh g−1), similar charge–discharge curves, and temporal stability owing to an irreversible modification of the pristine positive electrode during battery charge and discharge. This irreversibility stems from the dissolution and re-deposition of MnO2 and the formation of new manganese and zinc compounds (basic salt deposits such as ZnMn2O4, Mn2O3, and MnOOH). The additional (new) MnO2 phase is formed via two routes: disproportionation of Mn+3 ions formed during the discharge process and anodic oxidation of Mn2+ ions in a solution. According to X-ray diffraction and Raman spectroscopy analyses, the re-deposited MnO2 is in an amorphous state. The amorphous MnO2 covers the surface of the initial crystalline particles and affects the electrochemical behavior of the ZIBs. The strong pH dependence of the electrochemical response of the MnO2 electrodes is related to the H+ concentration effect on ionic equilibria in this system, such as the formation of basic zinc and manganese salts and hydroxides as well as the disproportionation of Mn+3 and anodic oxidation of Mn+2.

Selective electrochemical transformations of bismuth interlayers in (Bi2)m(Bi2Te3)n superlattices can be of interest as a means of thermoelectric materials design based on bismuth telluride. In this work, the interlayers in the electrodeposited (Bi2)m(Bi2Te3)n superlattice structures formed by pulse potential controlled electrodeposition were characterized with electrochemical microgravimetry on quartz crystal electrodes, cyclic voltammetry, potentiodynamic electrochemical impedance spectroscopy (PDEIS), and in situ Raman spectroscopy. The oxidation potential of bismuth in the interlayers is in between the potentials of metallic bismuth and bismuth telluride anodic oxidation, which allows electrochemical detection and selective anodic dissolution of the interlayer bismuth. Microgravimetry and cyclic voltammetry have provided monitoring of bismuth interlayer dissolution and the subsequent underpotential deposition (upd) of bismuth adatoms onto Bi2Te3 layers in the electrochemically created slits. PDEIS provided separate monitoring of the interfacial charge transfer, spatially restricted diffusion, capacitance of faradaic origin, and double-layer capacitance, which disclosed different variations of the electrochemical interface area in the superlattices with initial bismuth content below and above that of Bi4Te3. In situ Raman spectroscopy has monitored the removal of bismuth interlayers and distinguished different locations of Bi adatoms in two stages of Bi upd. The electrochemically created slits of molecular dimension have a potential of being used as sieves, e.g., to provide selective accessibility of the electrochemically created centers inside them to molecules and ions in multi-component solutions.

Selective electrochemical transformations of bismuth interlayers in (Bi 2 ) m (Bi 2 Te 3 ) n superlattices can be of interest as a means of thermoelectric materials design based on bismuth telluride. In this work, the interlayers in the electrodeposited (Bi 2 ) m (Bi 2 Te 3 ) n superlattice structures formed by pulse potential controlled electrodeposition were characterized with electrochemical microgravimetry on quartz crystal electrodes, cyclic voltammetry, potentiodynamic electrochemical impedance spectroscopy (PDEIS), and in situ Raman spectroscopy. The oxidation potential of bismuth in the interlayers is in between the potentials of metallic bismuth and bismuth telluride anodic oxidation, which allows electrochemical detection and selective anodic dissolution of the interlayer bismuth. Microgravimetry and cyclic voltammetry have provided monitoring of bismuth interlayer dissolution and the subsequent underpotential deposition (upd) of bismuth adatoms onto Bi 2 Te 3 layers in the electrochemically created slits. PDEIS provided separate monitoring of the interfacial charge transfer, spatially restricted diffusion, capacitance of faradaic origin, and double-layer capacitance, which disclosed different variations of the electrochemical interface area in the superlattices with initial bismuth content below and above that of Bi 4 Te 3 . In situ Raman spectroscopy has monitored the removal of bismuth interlayers and distinguished different locations of Bi adatoms in two stages of Bi upd. The electrochemically created slits of molecular dimension have a potential of being used as sieves, e.g., to provide selective accessibility of the electrochemically created centers inside them to molecules and ions in multi-component solutions.

We, for the first time, report potassium storage in carbon-modified Li4Ti5O12 spinel (C-LTO), where the carbon coating increases the electrical conductivity from similar to 10(-7) to similar to 10(-1) S cm(-1). C-LTO provides a high initial charge capacity of approximately 221 mAh g(-1) at 0.2C (34 mA g(-1)) with about 77% retention for 200 cycles. Pre-potassiation of C-LTO electrode successfully improved initial Coulombic efficiency. The excellent electrode performance is further emphasized at high rate (3.2C, 544 mA g(-1)), with an initial capacity of 130 mAh g(-1) and 70% retention for 1000 cycles. During the reaction in K cells, the incorporation of K+ ions into the cubic spinel Li4Ti5O12 induces a biphasic reaction, namely cubic rock salt K-rich K6LiTi5O12 and Li-rich Li7Ti5O12 phases accompanied by Ti4+/3+ redox, as confirmed by in-situ X-ray diffraction and ex-situ X-ray absorption analyses. The original Li4Ti5O12 spinel is recovered upon depotassiation. In addition, full cells paired with a P3-K-0.5[Mn0.8Fe0.1Ni0.1]O-2 cathode demonstrate the feasibility of applying the C-LTO electrode as an anode for high-rate and long-term potassium storage.

Electrochemical charge/discharge mechanisms in the electrophoretically deposited CdSe quantum dot (QD)film electrodes in NBu4PF6 acetonitrile solution have been investigated. The films were deposited from CdSe colloidal solution in nitrobenzene at variable QD size (diameter) from 3.4 to 6.3 nm onto transparent conducting glass substrates. Electrochemical behavior and optical response were characterized by cyclic voltammetry (CV) and in situ absorption spectroscopy. Electrochemical charging under an inert gas atmosphere results in a reversible color change (electrochromism), due to the bleach of exciton absorption with 0.3 optical density changes. The mechanism of electrochemical charging comprises electron transfer from conducting substrate to QD, interparticle transfer and also electron capturing by acceptors in solution. The introduction of a strong electron acceptor (O2) into the solution results in a suppression of electrochromism. The influence of oxygen is rather reversible which is observed from recovered electrochromic behavior after electrolyte resaturation with argon.

Underpotential deposition, i.e. the cathodic deposition above reversible potential E(Men+/Me), produces an atomic layer of a metal on a semiconductor electrode, such as e.g. bismuth telluride. This phenomenon allows electrodeposition of superlattices formed of building blocks of a layered semiconductor structure joined by biatomic metal interlayer. This work outlines the optimized pulse potential controlled electrodeposition of (Bi2)m(Bi2Te3)n films produced under mentioned above technique. The influence on the morphology of the electrodeposited films of key-parameters as applied pulse frequency, duty cycle, a routine of sodium dodecyl sulfate introduction in the electrolyte is discussed. The optimized procedure comprises a short (about 10 s) cathodic pre-treatment at high overpotential of the cathodic reaction, the subsequent periodic switching for 120 min between potentials of electrodeposition and refinement at 0.1 Hz and 5% duty cycle with addition of surfactant 60 min after the start of the electrodeposition.

Electrophoretically deposited (EPD) quantum dots (QDs) can be charged electrochemically via electron injection from a conducting substrate, leading to pronounced changes in their electrical and optical properties. The 180-550 nm thick EPD films composed of CdSe QDs with different diameters (2.8-6.3 nm) demonstrate a strong and reversible electrochromic response due to bleaching of excitonic transitions. The number of injected electrons was found to increase with QD size from 1.3 (QD diameter of 2.8 nm) to 6 (QD diameter of 6.3 nm) electrons per nanoparticle. As a result for 3.4 nm, 4.5 nm, and 6.3 nm QDs a complete 1Se level filling was observed, while the smallest studied QDs (2.8 nm) exhibited only a partial 1Se level population. In addition, 4.5 and 6.3 nm QDs also showed partial 1P(e) level filling with electrons. The data from both cyclic voltammetry measurements and electrochemically driven spectral bleaching enabled determining the electrochemically derived 1Se level energies. Additionally, we demonstrate fast charging-discharging kinetics for EPD CdSe QD films with complete absorption bleaching and recovery in a sub-100 ms time scale, which opens prospects for utilizing such films in various applications such as electrochromic displays, smart windows or tunable color filters for photography.

Herein, the promising properties of open‐structured NaV3O8 as a cathode material for Zn‐ion batteries (ZIBs) are investigated. First‐principles calculations predict the insertion of Zn2+ (0.74 Å) in NaV3O8 with an interlayer distance of ≈7 Å, enabling delivery of a high discharge capacity of 353 mAh g−1 at 70 mA g−1 (0.2 C) for 300 cycles in the operating window of 0.3−1.5 V in 1 m Zn(CF3SO3)2 aqueous solution. Operando synchrotron X‐ray diffraction, X‐ray absorption near edge structure spectroscopy, and first‐principles calculations validate the insertion of Zn2+ into the NaV3O8 structure within the operation range. Moreover, operando synchrotron X‐ray diffraction and operando Raman spectroscopy reveal the formation of layered zinc hydroxytriflate (Zn5(OH)8(CF3SO3)2∙xH2O) as a side reaction below 0.8 V on discharge (reduction) and its dissolution into the electrolyte above 0.8 V on charge (oxidation). The formation of the Zn hydroxytriflate interfacial layer increases the charge‐transfer activation energy from 15.5 to 48 kJ mol−1, leading to kinetics fade below 0.8 V. The findings reveal the charge‐storage mechanism for NaV3O8, which may also be applicable to other vanadate cathodes, providing new insights for the investigation and design of ZIBs.

Electrodeposition of metal adlayers on semiconductor metal chalcogenides (CdSe, CdS, PbTe, PbSe, PbS, Bi2Te3) is reviewed. Cathodic underpotential deposition of metal adlayer on metal chalcogenide is the electrochemically irreversible surface limited reaction. The irreversibility of the upd increases in the row from tellurides to selenides and further to sulfides. The underpotential shift on chalcogenide nanoparticles increases with particle size. Metal upd on chalcogenides is applied as a means of measurement of electroactive surface area of chalcogenide electrodes. The method is especially advantageous for multicomponent systems with other component not supporting upd, such as CdSe-TiO2, CdSe-ZnO. Differences of voltammetric profiles of Pb upd on Bi2Te3 and Te are applied for detection of Bi2Te3 surface contamination by elemental tellurium. The further tasks in the electrochemistry of metal adlayers are their incorporation as interlayers in layered chalcogenides and electrodeposition of superlattices.

Numerical simulations of current–voltage curves in electron-only devices are used to discuss the influence of charged defects on the information derived from fitting space-charge-limited current models to the data. Charged, acceptor-like defects lead to barriers impeding the flow of electrons in electron-only devices and therefore lead to a reduced current that is similar to the situation where the device has a built-in voltage. This reduced current will lead to an underestimation of the mobilities and an overestimation of characteristic tail slopes if analytical equations are used to analyze the data. Correcting for the barrier created by the charged defects can, however, be a successful way to still be able to obtain reasonably accurate mobility values. Introduction A frequently used method to analyze charge carrier transport in organic semiconductors is based on space-charge-limited current measurements performed on single carrier devices [1-14]. These devices consist of two contacts that are either both electron-injecting or both hole-injecting, meaning that the current–voltage curve of these devices is not determined by the recombination of electrons and holes in the volume of the device [15] but instead by the mobility and concentration of carriers and the electric field in the device. If a device with two electron injecting contacts were doped to be sufficiently n-type that the electron concentration were determined by the doping and not by the injected charges in a certain range of voltages, the current–voltage curve in that range would be essentially ohmic, and the conductivity of the system would depend on mobility and electron concentration [16,17]. If the electron-only device were, however, undoped and the injection at the contacts efficient, the current density J would to a first approximation not depend on the equilibrium electron concentration anymore. Instead J would just depend on the mobility μ, which is typically the only unknown parameter, as well as the voltage V, the device thickness d and the permittivity ε = ε0εr and would ideally follow the Mott–Gurney law [18,19] Beilstein J. Nanotechnol. 2013, 4, 180–188.

Superlattice structures of (Bi2)m(Bi2Te3)n series with controllable Bi mole fraction from 0.41 to 0.71 are electrodeposited in pulse potentiostatic mode from acidic electrolytes containing Bi(NO3)3 and TeO2 as precursors. Two valence states of bismuth in superlattices are identified by X-ray photoelectron spectroscopy (XPS). One of those states is attributed to interlayered Bi0 which is present in (Bi2)m(Bi2Te3)n superlattice in the form of biatomic layers between bismuth telluride quintuples. X-ray difraction (XRD) analysis and density functional theory (DFT) calculations indicate an increase in subcell parameter asub and decrease in subcell parameter csub with the increase of Bi mole fraction. Biatomic layers of Bi0 are identified with cyclic voltammetry by characteristic anodic peak between potentials of metallic bismuth and Bi2Te3 oxidation. The selective oxidation of Bi-bilayers in (Bi2)m(Bi2Te3)n superlattice at the potential of the anodic peak results in the product corresponding to Bi2Te3 by stoichiometry, but having an expanded crystal structure. Superlattices with controllable Bi mole fraction and Bi2Te3 with “memory effect” may be of interest for design of new thermoelectric materials with controllable parameters.

Nanostructured n-Bi2O3/p-CuBi2O4/p-CuO photocathodes with incident photon-to-current conversion efficiency IPCEmax = 70% (λ = 400 nm) have been prepared using electrochemical and chemical methods. Platelet-like BiOI nanocrystals electrochemically deposited on FTO substrate were used as precursors. CuI nanoparticles were deposited on the BiOI surface by successive ionic layer adsorption and reaction technique. Oxidative heat treatment of BiOI/CuI heterostructure in air leads to the formation of the Bi2O3/CuBi2O4/CuO composite. Binary oxide was formed as a result of solid-state interaction between bismuth and copper oxides at their interface. Spectral sensitization of wide-gap n-Bi2O3 (band gap Eg = 2.80 eV) with narrow-gap p-CuBi2O4 (Eg = 1.80 eV) and p-CuO (Eg = 1.45 eV) extends spectral sensitivity range up to 800 nm by Z-scheme implementation: cathodic photocurrent is associated with the transition of photoelectrons from p-CuBi2O4 and p-CuO to the solution, while photoholes recombine with electrons of n-Bi2O3 conduction band. High quantum efficiency of photocurrent was achieved due to band-edge correlation in a three-component oxide heterostructure, combined with an internal electric field in p-CuBi2O4 and effective photon absorption by two narrow-band-gap p-CuBi2O4 and p-CuO semiconductors.