Acidic Electrolyte Solution Research Articles

Potential-Dependent Structures and Potential-Induced Structure Changes at Pt(111) Single-Crystal Electrode/Sulfuric and Perchloric Acid Interfaces in the Potential Region between Hydrogen Underpotential Deposition and Surface Oxide Formation by In Situ Surface X-ray Scattering

Potential-dependent structures and potential-induced structure changes of the Pt(111) electrode in perchloric and sulfuric acid electrolyte solutions were investigated in the potential region between the underpotential deposition (UPD) of hydrogen (0.05 V vs RHE) and surface oxide formation (0.95 V) by in situ surface X-ray scattering (SXS) using the electrolyte thickness controllable spectroelectrochemical cell. In both solutions, the interfacial structures, including not only the surface arrangements of the adsorbates but also the Pt(111) surface atomic arrangements at various potentials, were accurately determined and compared with those previously reported in the literature. Several differences and new results when compared to the previously reported results were found by in situ potential-dependent structure measurements as follows: at 0.90 V, while oxygen species, such as an adsorbed hydroxyl group (OHad), H2O, and/or H3O+ with a total coverage of 1 monolayer (ML), are adsorbed on the atop site of t...

Molecular design of a novel ligand for Menshutkin complexation of Bi(iii) from aqueous acidic copper sulfate electrolyte solutions and experimental investigations

A novel silica functionalised phen–arene adsorbent exhibits reversible and highly selective adsorption of Bi(iii) over Cu(ii) ions by Menshutkin complexation from an aqueous acidic copper electrolyte solution.

Evaluation of manganese dioxide deposition on lead-based electrowinning anodes

In this study, the initial stages of the MnO2 electrodeposition on different lead-based electrowinning anodes (Pb–MnO2 and PbAg) in sulfuric acid electrolyte solutions were investigated. The MnO2 deposition and its preliminary effects on the oxidation of the anodes were studied using electrochemical techniques including potentiostatic polarization and linear potential sweep voltammetry. The potentiostatic polarizations were accompanied by chemical analysis of the electrolyte to investigate the manganese oxidation rates on the anodes. Scanning electron microscopy (SEM) was employed to characterize the deposited MnO2 layers. The presence of MnO2 particles on the Pb–MnO2 composite anode contributed to the deposition of a very uniform, dense, and stable MnO2 layer. The effects of the MnO2 composite particles in the composite anode on the current distribution, Mn3+ disproportionation rate and Mn2+ oxidation rate, were proposed as the possible causes of the observed properties of the MnO2 layer on this anode. The MnO2 layer on the Pb–MnO2 anode grew quickly during the initial stages. This layer became smoother over the course of polarization. Although the oxidation of the anodes was hindered by the deposited MnO2 layer, this effect was more significant on the composite anode than the conventional PbAg anode. This was attributed to different properties of the MnO2 layers deposited on these anodes.

Ion–ion correlation, solvent excluded volume and pH effects on physicochemical properties of spherical oxide nanoparticles

One major source of complexity in the implementation of nanoparticles in aqueous electrolytes arises from the strong influence that biological environments has on their physicochemical properties. A key parameter for understanding the molecular mechanisms governing the physicochemical properties of nanoparticles is the formation of the surface charge density. In this article, we present an efficient and accurate approach that combines a recently introduced classical solvation density functional theory for spherical electrical double layers with a surface complexation model to account for ion–ion correlation and excluded volume effects on the surface titration of spherical nanoparticles. We apply the proposed computational approach to account for the charge-regulated mechanisms on the surface chemistry of spherical silica (SiO2) nanoparticles. We analyze the effects of the nanoparticle size, as well as pH level and electrolyte concentration of the aqueous solution on the nanoparticle’s surface charge density and Zeta potential. We validate our predictions for 580Å and 200Å nanoparticles immersed in acid, neutral and alkaline mono-valent aqueous electrolyte solutions against experimental data. Our results on mono-valent electrolyte show that the excluded volume and ion–ion correlations contribute significantly to the surface charge density and Zeta potential of the nanoparticle at high electrolyte concentration and pH levels, where the solvent crowding effects and electrostatic screening have shown a profound influence on the protonation/deprotonation reactions at the liquid/solute interface. The success of this approach in describing physicochemical properties of silica nanoparticles supports its broader application to study other spherical metal oxide nanoparticles.

Instability Of Commercial Pt/C And Pd/C Electrocatalysts In Alkaline Media

The electrochemical degradation of commercial (E-TEK) Pt and Pd nanoparticles supported on Vulcan XC-72 (noted Pt/C and Pd/C) was performed in NaOH electrolyte solutions. The fate of the electrocatalysts upon accelerated stress test (AST) in alkaline medium was compared to that in acidic (H2SO4 and HClO4) electrolyte solutions. Electrochemical measurements, combined with Identical-Location Transmission Electron Microscopy (ILTEM) demonstrated that the Pt/C catalyst degradation in 0.1 M NaOH at 25°C is extremely severe for a mild accelerated stress test (AST – 150 cycles, at 100 mV sec-1 and 25°C, between 0.1 and 1.23 V vs. RHE), mainly owing to large nanoparticles detachment from the carbon substrate. For Pd/C, an opposite trend is found: the degradations are harsher in acidic environment.

The performance of Pb–MnO2 and Pb–Ag anodes in 2 Mn(II)-containing sulphuric acid electrolyte solutions

In this study, electrochemical performances of the Pb–MnO2 composite anodes in sulphuric acid electrolyte containing different manganese concentrations were investigated. The anodic electrodeposited MnO2 layers on the composite anodes were studied and their properties were compared with those of an industrial Pb–Ag anode.The electrochemical impedance spectroscopy (EIS) and potentiostatic polarizations were accompanied by chemical analysis of the electrolyte to investigate the Mn(II) oxidation and oxygen evolution rates on the fresh anodes. The long term effect of the deposited MnO2 on the electrocatalytic properties of the anodes was studied by galvanostatic polarizations. The results revealed that the Pb–MnO2 anodes operate at lower potentials than the Pb–Ag anodes in a Mn-free electrolyte, indicating higher electrocatalytic activity of the composite anode. The Mn(II) oxidation proceeded at different rates on the Pb–Ag and Pb–MnO2 anodes. The oxygen evolution reaction was depolarized in the presence of Mn(II) ions. However, formation of the MnO2 layers might lead to higher anodic potentials. Scanning electron microscopy (SEM), X-ray photoelectron spectrometer (XPS) and X-ray diffraction (XRD) were utilized to characterize the deposited MnO2 layers and also the corrosion product layers on the anodes. The MnO2 layers on the anodes were found to have different properties. While MnO2 layers on the composite anodes were uniform, compact and adhesive, the deposited layers on the Pb–Ag anodes were flaky, porous, and loosely adhered. These layers provided the anodes with different degree of protection against electrochemical oxidation.

Nafion Coated Lithium Ion Conducting Ceramic for Aqueous Li-Air Batteries

Protected lithium anodes use a lithium ion conducting ceramic membrane to separate the anode side and the cathode side, making it possible to use aqueous catholytes in a Li-air battery. However, this ceramic membrane is not chemically stable in acidic or alkaline electrolyte solutions. In order to extend the operational life of this protecting ceramic, modifications of its surface are needed. In this work, we coat the ceramic membrane with a thin layer of lithiated Nafion. Nafion coatings were obtained by using a doctor-blade method, with a typical thickness in the range of 6 to 10 μm. Electrochemical impedance spectroscopy showed that the Nafion coatings lead to a small increase in the membrane resistance. The coated ceramic showed better capacity and stability in cell performance when tested in extended discharge.

Synthesis and Electrochemical Properties of Nanocuboid and Nanofiber WO3

The present research work focused on the one step hydrothermal synthesis of monoclinic nanocuboid and hexagonal nanofiber WO3 from common precursors and different structure directing reagents for high performance electrochromism. The characteristic phase and bonding behaviour depicts the probable intercalation space difference between these nanostructured particles. Electron – proton interaction mechanism of both WO3 coated transparent indium doped tin oxide (ITO) electrode depends on the concentration of acid electrolyte solution and electrochemical scan rate. A correlation between the crystal structures and morphology is evaluated for the fabricated films that exhibits enhanced electrochromic performance. Nanofiber WO3 exhibits high electrochromic reversibility of 78.94%, fast switching speeds of 6.02 s and 5.5 s for coloration and bleaching, respectively and high coloration efficiency of 54.09 cm2 C−1 in comparison to the monoclinic WO3 nanocuboid because of specious intercalation zone and wide open channels in hexagonal crystal structure, and interactive fiber morphology.

High-performance super capacitors based on activated anthracite with controlled porosity

Mongolian anthracite is chemically activated using potassium hydroxide as an activation agent to make activated carbon materials. Prior to the chemical activation, the chemical agent is introduced by two different methods as follows, (1) simple physical mixing, (2) impregnation. The physical properties such as specific surface area, pore volume, pore size distribution, and adsorption energy distribution are measured to assess them as carbon electrode materials for electric double-layer capacitors (EDLC). The surface functional groups and morphology are also characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analyses respectively. The electrochemical results for the activated carbon electrodes in 3 M sulfuric acid electrolyte solution indicate that the activated Mongolian anthracite has relatively large specific capacitances in the range of 120–238 F g−1 and very high electrochemical stability, as they keep more than 98% of initial capacitances until 1000 charge/discharge cycles.

Electrochemical Doping of Compact TiO2 Thin Layers

Electrochemical n-doping of dense thin films of TiO2 (anatase) occurs upon proton insertion from acidic aqueous electrolyte solution. Details of the reaction are investigated by cyclic voltammetry and by electrochemical impedance spectroscopy. The good-quality films are ideally compact, mimicking the properties of a macroscopic single-crystal electrode. The n-doping is stable for at least weeks of electrode storage in air at room temperature. Doping manifests itself by characteristic morphological differences of the surface. Electrochemical Li+ insertion indicates that there is a competition between Li+ and H+ ions in the lattice, detectable by cyclic voltammetry.

High Efficient Electrochromic WO3 Nanofibers

Hydrothermal synthesis facilitates the hierarchical growth of hexagonal WO3 nanofibers that consist of high interactive space and surface area. Prime processing parameters known as hydrothermal temperature, time and directional growth reagent sodium chloride concentration synchronizes both of the hexagonal crystal structure and nanostructured 1D fibrous morphology of WO3. Hexagonal nanofiber WO3 has specific surface area of 25.2m2/gm and their dip coated WO3/ITO glass substrate exhibits uniform thickness, interconnectivity and high degree of electrochromic properties. The optimized dip coated electrode depicts the current density of 8.9mA/cm2, excellent cyclic stability and the coloration efficiency in high acidic electrolyte solution. Crystal structure, morphology formation and their electrochromic responses are illustrated to support the fabrication of electrochromic device.

Electrochemical behavior of rolled Pb–0.8%Ag anodes in an acidic zinc sulfate electrolyte solution containing Cl− ions

In this study, the oxygen evolution kinetics and oxide layer properties of Pb–0.8%Ag rolled-alloy anodes were investigated during 15d of galvanostatic electrolysis in an acidic zinc sulfate electrolyte solution containing 600mg·L−1 Cl− ions. Cyclic voltammetry, quasistationary polarization, and electrochemical impedance spectroscopy were used to investigate the anode process. The microscopic morphology and phase composition of the anodic oxide layers were observed by scanning electron microscopy and X-ray diffraction, respectively. The observable variations in the electrocatalytic activity and reaction kinetics of the anodes during electrolysis indicate the formation and stabilization of the anodic oxide layer. With prolonged electrolysis, the oxygen evolution overpotential in the anodes mainly exhibited a decreasing trend, which is contrary to the trend of the electrode surface exchange current density. This depolarization may have been caused by the increasing roughness of the anodic surface and the catalytic effects of α-PbO2 and β-PbO2. As electrolysis continued, the cathodic peak (α-PbO2→PbSO4) mainly showed an increasing trend and gradually moved toward the negative direction. After 15days of electrolysis, the oxide layers exhibited a severely corrosive microstructure with plenty of cavities and etch pits. The uniform, well-defined crystal grains and regularity were not appeared. The phase composition of the anodic oxide layer was formed after 6d of electrolysis. α-PbO2 proved to be the main peak and showed preferential growth orientations along the (111) planes of the anodic oxide layer.

Ultrathin Anodic Aluminum Oxide Membranes for Production of Dense Sub-20 nm Nanoparticle Arrays

We present a systematic study of membrane structure (pore diameter and arrangement) in anodized aluminum oxide (AAO) layers obtained by anodization voltages 8-20 V in sulfuric and 15-40 V in oxalic acid electrolyte solutions. Anodization of bulk aluminum in sulfuric acid at 10 V potential was found to be optimal for production or ultrathin freestanding membranes with pore diameter in sub-20 nm range. The developed process with slow electrochemical reaction results in AAO membranes with thickness below 70 nm. The minimum required time for formation of continuous AAO membrane was determined and influence of electrolyte concentration on pore diameter in membrane after barrier layer removal analyzed. Finally, we demonstrate a method of membrane transfer onto a different surface and using it for masked deposition of dense nanoparticle arrays with diameters below 20 nm.

Potential Dependent Structures at Pt(111) Single Crystal Electrode/Electrolyte Interfaces Studied By Surface X-ray Scattering

Introduction. Platinum is one of the most important materials for various applications, and structure and properties of low index surfaces of single-crystal platinum have been extensively studied not only in ultrahigh vacuum (UHV) [1,2] but also in electrochemical environments [3-5]. It is very important to know potential dependent structures at Pt single-crystal electrode surface, especially in pre-oxide potential region, in situ, because of application for polymer electrolyte fuel cell (PEFC) as a cathode catalyst. Since there are few surface techniques to investigate the interfacial structures in situ, however, they have not been made clarified yet. The surface X-ray scattering (SXS) technique is one of the best methods to investigate the three-dimensional (3D) interfacial structure at an atomic level. Many in situ structural studies at electrode/electrolyte interfaces using the SXS technique have been carried out in the last 2 decades. For example, we determined the potential dependent structures at Au(111) and Au(100) single-crystal electrode/sulfuric acid electrolyte interfaces using this in situ technique [6]. In this study, the potential dependent structures of single-crystal Pt(111) electrode in perchloric acid and sulfuric acid electrolyte solutions in the potential regions between 0 V and +0.8 V (vs. Ag/AgCl) were investigated by in situ SXS measurements. Experimentals. Prior to each measurement, the Pt(111) disk was annealed at 1600°C for more than 1 hour using induction heater under argon/hydrogen atmosphere, and then quenched by ultrapure water saturated with argon/hydrogen. After that, the Pt(111) disk was set to the home-made SXS cell [7], the SXS cell was set to the 6-axes diffractometer, which was installed at undulator beamline BL3A in Photon Factory, and then in situ SXS measurements were carried out. Results and Discussion Figure 1 shows (00) rods of the Pt(111)/HClO4 interface measured at 0 V and 0.8 V. Based on the fitting of these data, we confirmed that at 0 V in hydrogen UPD potential region, layer distance between first and second outermost Pt layers is expanded by ca. 3 % because of strongly adsorbed hydrogen. We also found that at 0.8 V where pre-oxidation is completely finished, oxygen species are adsorbed at an atop site on the Pt(111)-(1x1) surface with a (1x1) structure. Detailed structure analyses at the other potentials, potential dependent structure analyses at Pt(111)/H2SO4 interfaces, and their dynamic studies are now under investigation.Figure 1. (00) rods at Pt(111)/perchloric acid solution interface measured at 0 V and 0.8 V. Circles and solid line represent data points and fitting curves, respectively.Acknowledgement. This work was supported by and conducted at the Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN) in NIMS.References.[1] M. Wakisaka, et al., Langmuir, 25 (2009) 1897.[2] M. Nakamura, et al., Surf. Sci., 563 (2004) 199.[3] J. Clavilier, et al., J. Electroanal. Chem., 107 (1980) 205.[4] K. Sashikata, et al., J. Vac. Sci. Tech. B, 9 (1991) 457.[5] C. A. Lucas, et al., Physica B, 221 (1996) 245.[6] T. Kondo, et al., J. Phys. Chem. C, 111 (2007) 13197.[7] T. Kondo, et al., Electrochim. Acta, 47 (2002) 3075.

A zeolite ion exchange membrane for redox flow batteries

The zeolite-T membrane was discovered to have high proton permselectivity against vanadium ions and exhibit low electrical resistance in acidic electrolyte solutions because of its enormous proton concentration and small thickness. The zeolite membrane was demonstrated to be an efficient ion exchange membrane in vanadium redox flow batteries.

Electrochemical capacitance performance of titanium nitride nanoarray

• TiN nanoarray is formed by a nitridation process of TiO 2 in ammonia atmosphere. • TiN nanoarray exhibits much higher EDLC capacitance than TiO 2 nanoarray. • The specific capacitance of TiN nanoarray achieves a high level of 99.7 mF cm −2 . • A flexible solid-state supercapacitor is constructed by TiN nanoarray and PVA gel. In this study, titanium nitride (TiN) nanoarrays with a short nanotube and long nanopore structure have been prepared by an anodization process of ultra thin titanium foil in ethylene glycol (EG) solution containing ammonium fluoride, subsequent calcination process in an air atmosphere, and final nitridation process in an ammonia atmosphere. The morphology and microstructure characterization has been conducted using field emission scanning electron microscope and X-ray diffraction. The electrochemical properties have been investigated through cyclic voltammetry and electrochemical impedance spectrum measurements. The electrochemical capacitance performance has been investigated by galvanostatic charge–discharge measurements in the acidic, neural and alkali electrolyte solution. Well-defined TiN nanoarrays contribute a much higher capacitance performance than titania (TiO 2 ) in the supercapacitor application due to the extraordinarily improved electrical conductivity. Such an electrochemical capacitance can be further enhanced by increasing aspect ratio of TiN nanoarray from short nanotubes to long nanopores. A flexible supercapacitor has been constructed using two symmetrical TiN nanoarray electrodes and a polyvinyl alcohol (PVA) gel electrolyte with H 2 SO 4 –KCl–H 2 O–EG. Such a supercapacitor has a highly improved potential window and still keeps good electrochemical energy storage. TiN nanoarray with a high aspect ratio can act well as an ultra thin film electrode material of flexible supercapacitor to contribute a superior capacitance performance.

Polyaniline/poly(vinyl alcohol) (PAN/PVA) composite films: the synergy of film structural stiffening, redox amplification, and mobile species compositional dynamics

In this work, we report an unexpected but significant improvement of the redox behavior of conducting polyaniline (PAN) films by trapping intrinsically nonconducting poly(vinyl alcohol) (PVA) in the matrix of the polymer acting as stiffening and/or cross-linking agents. Film structural stiffening of PAN/PVA inclusion was studied in relation to film compositional dynamics. PAN and PAN/PVA composite films were potentiodynamically deposited using high-frequency electrochemical quartz crystal microbalance under electrochemical potentiodynamic control. From the simultaneously obtained measurements of nanogravimetric and cyclic voltammetric data, it has been found that the presence of PVA in the deposition solution increased the rate of PAN film growth as a function of PVA concentration. Characterization of the resultant composite films in monomer-free acidic electrolyte solutions showed significantly enhanced redox behavior of PAN/PVA composite films (with different PVA contents) compared to pure PAN by a factor of ∼2–4. For the study of structure–composition relationships of composite polymer films, fluxes of instantaneous mobile species dynamics (ion/solvent) as a function of film redox conversion and potential cycling were correlated with film structural stiffening and the observed unusual redox enhancement of PAN/PVA composite films. Using various experimental timescales, we were able to resolve bound (associated with ion transfer) and free solvent compositional dynamics (associated with thermodynamic activity balance).

Interactions between Individual Charged Dendronized Polymers and Surfaces

Polymethacrylate-based amino-terminated dendronized polymers up to generation 5 were adsorbed on mica, hydrophobized mica, and gold and studied with the atomic force microscope (AFM). These studies were carried out in a mildly acidic electrolyte solution where these polymers are fully ionized. The polymers were imaged in intermitted contact mode in solution, and desorption forces of individual polymer chains were investigated by single molecule force spectroscopy. The adsorbed chains have a uniform envelope up to generation 4, but the generation 5 polymer has a pronounced pearl-necklace structure. Force spectroscopy clearly reflects this difference. While lower generation polymers show peeling events with a single force plateau or pulling event with a single spike, those of generation 5 are characterized by two different force plateaus as well as multiple pulling events. These features are probably related to the unwrapping of pearls in the polymer backbone. We suspect that the pearls result from the high hydrophobicity of the polymer backbone.

Correlation between the capacitor performance and pore structure of ordered mesoporous carbons

Mesoporous carbons were synthesized by organic–organic self-assembly of triblock copolymer F127 and phenolic resin oligomers composed of resorcinol–formaldehyde or resorcinol–furfural. The mesostructure control was performed by using different polymerization catalysts, ammonia and acetic acid. The effects of the aldehyde and polymerization catalyst on pore architecture of mesoporous carbons were investigated. Disordered mesostructure with poorly disconnected mesopores was formed using furfural. In contrast, when formaldehyde was used, ordered structure with mesochannels was formed. In addition, changes in mesochannel length and the degree of long-range order are found to depend on polymerization catalyst. The porous carbons with different structure were used as a model material to investigate the ion storage/transfer behavior in electrical double-layer capacitor. Electrochemical cyclic voltammetry measurements were conducted in 1M sulfuric acid electrolyte solution. The ordered mesoporous carbons show superior capacitances and rate performance over the disordered carbons. Electrochemical impedance spectroscopy was used to assess the transport properties. The impedance data clearly demonstrated that the degree of long-range order and channel length can influence the ion transport, resulting in superior capacitive performances.

DNA hydrogel-based supercapacitors operating in physiological fluids

DNA nanostructures have been attractive due to their structural properties resulting in many important breakthroughs especially in controlled assemblies and many biological applications. Here, we report a unique energy storage device which is a supercapacitor that uses nanostructured DNA hydrogel (Dgel) as a template and layer-by-layer (LBL)-deposited polyelectrolyte multilayers (PEMs) as conductors. Our device, named as PEM-Dgel supercapacitor, showed excellent performance in direct contact with physiological fluids such as artificial urine and phosphate buffered saline without any need of additional electrolytes, and exhibited almost no cytotoxicity during cycling tests in cell culture medium. Moreover, we demonstrated that the PEM-Dgel supercapacitor has greater charge-discharge cycling stability in physiological fluids than highly concentrated acid electrolyte solution which is normally used for supercapacitor operation. These conceptually new supercapacitors have the potential to be a platform technology for the creation of implantable energy storage devices for packageless applications directly utilizing biofluids.