Selective Determination of Copper (II) Based on Aluminum Silicon Carbide Nanoparticles Modified Glassy Carbon Electrode by Square Wave Stripping Voltammetry

The morphology and structure of as‐prepared aluminum silicon carbide (Al₄SiC₄) were characterized using X‐ray diffraction (XRD) patterns, scanning electron microscope (SEM), transmission electron microscopy (TEM) and UV‐vis spectra. The Al₄SiC₄ nanoparticles modified glassy carbon electrode (GCE) was further investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Based on this, this kind of new electrode was used for the detection of trace Cu²⁺ by square wave anodic stripping voltammetry (SWASV) for the first time. The electrochemical parameters influencing on deposition and stripping of metal ions, such as supporting electrolytes, pH value, deposition potential and deposition time, were also optimized. The results showed that the Al₄SiC₄ modified GCE exhibited excellent stripping response of Cu²⁺ and the stripping peaks response increased linearly with increasing concentration of Cu²⁺ in the ranges of 400 to 2200 nM. Under the optimized conditions the favorable sensitivity of the Al₄SiC₄ modified GCE toward trace Cu²⁺ was 1.49 μA μM⁻¹ and the limit of detection (S/N=3) was estimated to be 2.76 nM. More importantly, Al₄SiC₄ modified GCE had an excellent stability and negligible interference from other coexisting metal ions in the electrochemical determination of Cu²⁺.     

Preparation and characterization on the carbon nanotube chemically modified electrode grown in situ

Carbon nanotube chemically modified electrode (CNT-CME) was prepared by growing carbon nanotube (CNT) in situ on the pretreated graphite electrode (GE) via the catalytic chemical vapor deposition. The pretreated GE was prepared by ultrasonic immersion method using Ni(NO₃)₂ as the catalyst. The CNT growing on the CNT-CME was characterized by transmission electron microscope and scanning electron microscope. The obtained electrode electrochemical performance was characterized by cyclic voltammetry with the Na₂SO₄ solution and [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ solution. The results showed that the obtained electrode has good current responsive sensitivity and good testing result accuracy, indicating that the obtained electrode may have great application in electrochemical testing field.     

Electrophoretic deposited MWCNT composite graphite pencils and its uses to determine hyperin

A simple, fast, and effective method of fabricating electrochemical sensors using composite pencil graphite (CPG) lead modified with carboxylic multiwalled carbon nanotube (c-MWCNT) via electrophoretic deposition (EPD) has been developed. The EPD of c-MWCNT film on the CPG electrode (CPGE) was carried out at a constant applied potential of 25?V and deposition time of 1?min. The electrochemical performances of the modified CPGE, i.e., c-MWCNT/CPGE, in Fe(CN) ₆ ^4?/3? has been studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The c-MWCNT/CPGE has better current density, onset potentials, and charge transfer resistances than the CPGE. The c-MWCNT/CPGE has been successfully used to analyze hyperin in dry fruits of Acanthopanax sessiliflorus.     

A highly sensitive electrochemical sensor for simultaneous determination of hydroquinone and bisphenol A based on the ultrafine Pd nanoparticle@TiO2 functionalized SiC

A titanium dioxide–silicon carbide nanohybrid (TiO₂–SiC) with enhanced electrochemical performance was successfully prepared through a facile generic in situ growth strategy. Monodispersed ultrafine palladium nanoparticles (Pd NPs) with a uniform size of ∼2.3 nm were successfully obtained on the TiO₂–SiC surface via a chemical reduction method. The Pd-loaded TiO₂–SiC nanohybrid (Pd@TiO₂–SiC) was characterized by transmission electron microscopy and X-ray diffractometry. A method for the simultaneous electrochemical determination of hydroquinone (HQ) and bisphenol A (BPA) using a Pd@TiO₂–SiC nanocomposite-modified glassy carbon electrode was established. Utilizing the favorable properties of Pd NPs, the Pd@TiO₂–SiC nanohybrid-modified glassy carbon electrode exhibited electrochemical performance superior to those of TiO₂–SiC and SiC. Differential pulse voltammetry was successfully used to simultaneously quantify HQ and BPA within the concentration range of 0.01–200 μM under optimal conditions. The detection limits (S/N = 3) of the Pd@TiO₂–SiC nanohybrid electrode for HQ and BPA were 5.5 and 4.3 nM, respectively. The selectivity of the electrochemical sensor was improved by introducing 10% ethanol to the buffer medium. The practical application of the modified electrode was demonstrated by the simultaneous detection of HQ and BPA in tap water and wastewater samples. The simple and straightforward strategy presented in this paper are important for the facile fabrication of ultrafine metal NPs@metal oxide–SiC hybrids with high electrochemical performance and catalytic activity.     

MWCNTs/metal (Ni, Co, Fe) oxide nanocomposite as potential material for supercapacitors application in acidic and neutral media

Supercapacitive properties of synthesised metal oxides nanoparticles (MO where M = Ni, Co, Fe) integrated with multi-wall carbon nanotubes (MWCNT) on basal plane pyrolytic graphite electrode (BPPGE) were investigated. Successful modification of the electrode with the MWCNT-MO nanocomposite was confirmed with spectroscopic and microscopic techniques. Supercapacitive properties of the modified electrodes in sulphuric acid (H₂SO₄) and sodium sulphate (Na₂SO₄) electrolytes were investigated using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic constant current charge–discharge (CD) techniques. The specific capacitance values followed similar trend with that of the cyclic voltammetry and the electrochemical impedance experiments and are slightly lower than values obtained using the galvanostatic charge–discharge cycling. MWCNT-NiO-based electrode gave best specific capacitance of 433.8 mF?cm^?2 (ca 2,119 F?g^?1) in H₂SO₄. The electrode exhibited high electrochemical reproducibility with no significant changes over 1,000 cyclic voltammetry cycles.     

An Exfoliated Graphite Based Electrochemical Sensor for As(III) in Water

In this work, we present the application of an exfoliated graphite electrode modified with gold nanoparticles (AuNPs) for the detection of As(III) in acidic media. Gold nanoparticles were deposited on the surface of an exfoliated graphite electrode by electrodeposition at a potential window of ?0.2 V to 1.2 V. This was followed by activation in 0.5 M H₂SO₄ with 10 cycles from 0.6 V to 1.4 V. The modification of exfoliated graphite (EG) showed an increased electroactive surface area of the electrode and improved peak current output in a Fe(CN)₆^3?/4? redox probe. EG‐AuNPs electrode was used to detect As(III) in 1.0 M HNO₃ using square wave anodic stripping voltammetry (SWASV) technique at optimum conditions of pH 3, deposition potential of ?0.8 V, deposition time of 180 s, frequency of 5 Hz and pulse amplitude of 50 mV. The EG‐AuNPs electrode detected As(III) in solution to a limit of 0.58 ppb with regression of 0.9993. The method reported is simple, cheap and possesses good reproducibility. The developed electrochemical sensor was applied in the detection of As (III) in an industrial real water sample. The results of the real water sample analysis from the developed method are comparable with the inductively coupled plasma – optical emission spectroscopy (ICP‐OES) results.     

Bifunctional polydopamine@Fe3O4 core–shell nanoparticles for electrochemical determination of lead(II) and cadmium(II)

The present paper has focused on the potential application of the bifunctional polydopamine@Fe₃O₄ core–shell nanoparticles for development of a simple, stable and highly selective electrochemical method for metal ions monitoring in real samples. The electrochemical method is based on electrochemical preconcentration/reduction of metal ions onto a polydopamine@Fe₃O₄ modified magnetic glassy carbon electrode at −1.1 V (versus SCE) in 0.1 M pH 5.0 acetate solution containing Pb²⁺ and Cd²⁺ during 160 s, followed by subsequent anodic stripping. The proposed method has been demonstrated highly selective and sensitive detection of Pb²⁺ and Cd²⁺, with the calculated detection limits of 1.4 × 10⁻¹¹ M and 9.2 × 10⁻¹¹ M. Under the optimized conditions, the square wave anodic stripping voltammetry response of the modified electrode to Pb²⁺ (or Cd²⁺) shows a linear concentration range of 5.0–600 nM (or 20–590 nM) with a correlation coefficient of 0.997 (or 0.994). Further, the proposed method has been performed to successfully detect Pb²⁺ and Cd²⁺ in aqueous effluent.     

Formation of solid electrolyte films on porous supporting electrodes

In this work, the method of chemical deposition from the gas phase of organometallic compounds (CVDOM) was used to obtain thin electrolyte films of zirconia stabilized by yttria (YSZ) on a supporting electrode. Tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)zirconium and tris(2,2,6,6-tetramethyl-3,5-heptanedionato)yttrium often termed as zirconium (IV) Zr(dpm)₄ and yttrium (III) Y(dpm)₃ dipivaloylmethanates were used as precursors for film deposition. Gas-tight electrolyte films were obtained on a supporting anode with a thickness of 4–10 μm at moderate deposition temperatures of 500–700°C. An electrochemical cell was prepared and tested using the obtained films. The cell allowed obtaining the power density values of 680, 360, and 175 mW/cm² at the temperatures of 800, 700, and 600°C, accordingly.     

Safety improvement of lithium ion batteries by organo-fluorine compounds

Thermal stability, electrochemical oxidation stability and charge/discharge characteristics of natural graphite powder were investigated by mixing of five fluoro-carbonates with 1 mol/L LiClO₄–EC/DEC/PC (1:1:1 vol.). DSC study revealed that thermal stability of the electrolyte solution was improved by mixing of fluoro-carbonates by 10.0–33.3 vol.%. Electrochemical oxidation stability was also improved. Oxidation currents for Pt electrode significantly decreased by mixing of fluoro-carbonates. In the fluoro-carbonate-mixed electrolyte solutions, electrochemical reduction of PC decreased with increasing concentration of fluoro-carbonate and current density. As a result, first coulombic efficiency for natural graphite electrode increased, that is, irreversible capacity decreased in the fluoro-carbonate-mixed solutions.     

Thin films of metal dibenzotetraaza [14] annulene complexes.: Part 3. Dimerization and alternated dimerizations of γ-substituted Ni complexes

The electrochemical behaviour of some Ni γ-monosubstituted dibenzotetraaza [14] annulene complexes has been investigated. The oxidation in CH₂Cl₂ of the complex containing a 4-carboxybenzyl group leads to the corresponding γ-γ dimer whose electrochemical properties have been studied. The electrode surface can be coated by thin films of this dimer using CH₃CN instead of CH₂Cl₂; however, the resulting modified electrode is poorly stable. The oxidation of the complex containing 1-(4-carboxybenzyl)pyrrole as γ substituent involves γ-γ dimer formation before the formation of a regular polypyrrole film. The film displays reversible electrochemical reduction of the metal centre (Ni(II)/Ni(I)) and two successive oxidations of the macrocycle (Mc/Mc^•+ and Mc^•+/Mc²⁺). The complex containing a bromo(4-carboxybenzyl) group offers an unusual feature in that polymeric films can be obtained following an original procedure based on alternated dimerizations. This is a consequence of the formation of two different dimers obtained by anodic and cathodic processes.     

Electrochemical preparation of oxide materials for electrochemistry and electronics

Electrochemical formation of barium tungstate (BaWO₄) was studied as a model case of electrochemical formation of an advanced oxide material for electronics. BaWO₄ is formed on the surface of tungsten electrode during oxidation in alkaline media (pH > 12) containing a corresponding cation. The analysis of electrochemical as well as electrochemical quartz crystal microbalance (EQCM) data taken during these experiments identifies at least three qualitatively different steps composing the electrode process. Effects of the potential, applied current density and alkaline earth metal cation concentration are demonstrated using cyclic voltammetry and galvanostatic experiments. Specific constraints of the ECC formalism for the electrochemical oxide deposition following from the galvanostatic data are discussed. Received: 2 October 1997 / Accepted: 4 December 1997     

Effects of current densities on the formation of LiCoO<Subscript>2</Subscript>/graphite lithium ion battery

The activation characteristics and the effects of current densities on the formation of a separate LiCoO₂ and graphite electrode were investigated and the behavior also was compared with that of the full LiCoO₂/graphite batteries using various electrochemical techniques. The results showed that the formation current densities obviously influenced the electrochemical impedance spectrum of Li/graphite, LiCoO₂/Li, and LiCoO₂/graphite cells. The electrolyte was reduced on the surface of graphite anode between 2.5 and 3.6 V to form a preliminary solid electrolyte interphase (SEI) film of anode during the formation of the LiCoO₂/graphite batteries. The electrolyte was oxidized from 3.95 V vs Li⁺/Li on the surface of LiCoO₂ to form a SEI film of cathode. A highly conducting SEI film could be formed gradually on the surface of graphite anode, whereas the SEI film of LiCoO₂ cathode had high resistance. The LiCoO₂ cathode could be activated completely at the first cycle, while the activation of the graphite anode needed several cycles. The columbic efficiency of the first cycle increased, but that of the second decreased with the increase in the formation current of LiCoO₂/graphite batteries. The formation current influenced the cycling performance of batteries, especially the high-temperature cycling performance. Therefore, the batteries should be activated with proper current densities to ensure an excellent formation of SEI film on the anode surface.     

Target-induced formation of gold amalgamation on DNA-based sensing platform for electrochemical monitoring of mercury ion coupling with cycling signal amplification strategy

Heavy metal ion pollution poses severe risks in human health and environmental pollutant, because of the likelihood of bioaccumulation and toxicity. Driven by the requirement to monitor trace-level mercury ion (Hg²⁺), herein we construct a new DNA-based sensor for sensitive electrochemical monitoring of Hg²⁺ by coupling target-induced formation of gold amalgamation on DNA-based sensing platform with gold amalgamation-catalyzed cycling signal amplification strategy. The sensor was simply prepared by covalent conjugation of aminated poly-T₍₂₅₎ oligonucleotide onto the glassy carbon electrode by typical carbodiimide coupling. Upon introduction of target analyte, Hg²⁺ ion was intercalated into the DNA polyion complex membrane based on T–Hg²⁺–T coordination chemistry. The chelated Hg²⁺ ion could induce the formation of gold amalgamation, which could catalyze the p-nitrophenol with the aid of NaBH₄ and Ru(NH₃)₆³⁺ for cycling signal amplification. Experimental results indicated that the electronic signal of our system increased with the increasing Hg²⁺ level in the sample, and has a detection limit of 0.02 nM with a dynamic range of up to 1000 nM Hg²⁺. The strategy afforded exquisite selectivity for Hg²⁺ against other environmentally related metal ions. In addition, the methodology was evaluated for the analysis of Hg²⁺ in spiked tap-water samples, and the recovery was 87.9–113.8%.     

Enhanced catalytic activity of ppy-coated pencil electrode in the presence of chitosan and Au nanoparticles for hydrogen evolution reaction

Catalytically active and low-cost electrocatalysts for the production of hydrogen from water are extremely important for future renewable energy systems. Here, we report the fabrication of a facile pencil graphite electrode modified with polypyrrole-chitosan/Au nanoparticles and tested its performance for electrocatalytic hydrogen evolution reaction (HER) as a model process. The porous surface of the pencil graphite electrode (PGE) was modified potentiostically by polypyrrole (PPy) at various film thicknesses in the presence of chitosan (Chi), which is a natural biopolymer, in the electrolyte medium. After the optimum film thickness had been obtained, the Au particles electrodeposited on to the PPy/Chi composite film at the nano-scale to benefit both from its well-known high catalytic activity and to reduce the amount of precious metal Au to prepare a low-cost eletrocatalyst. The performance of this composite catalyst on the H⁺ reduction (H_ad formation) and thereby on the hydrogen evolution was investigated. Data from cyclic voltammetry (CV), Tafel polarization curves, and electrochemical impedance spectroscopy (EIS) demonstrated that the current densities related to the electron transfer rate changed with the thickness of the composite film, and the catalytic activity was enhanced more with deposition small amount of Au on to the catalyst surface.     

Zinc sulfide surface formation on Hg electrode during cyclic voltammetric scan: an implication for previous and future research studies on metal sulfide systems

Cyclic voltammetry on the Hg electrode was used to investigate the electrochemical behavior of NaCl/NaHCO₃ electrolyte solutions supersaturated with respect to Zn sulfide phases. The voltammetric results clearly show how an Hg electrode, due to exchange between Hg²⁺ from an HgS_adlayer and Zn²⁺ from solution, becomes the site for surface ZnS_adlayer formation in the potential range ?0.45 to ?0.6?V. The exchange reaction is reversible, and the surface-formed ZnS_adlayer persists at the Hg electrode surface until ?1.3?V during cathodic scans. Near ?1.3?V, it is reduced. In the same solution, evidence for reduction of bulk Zn sulfide species including nanoparticles was not obtained. The approach emphasized here can be readily extended to any other system consisting of metal electrode and chalcogenide anions, pointing to the importance of choosing experimental conditions (i.e., deposition potential, stirring, and accumulation times) to avoid artifacts and wrong interpretation of data due to surface formation of metal sulfide species.     

Electrochemical Characterization of Chemically Synthesized Polythiophene Thin Films: Performance of Asymmetric Supercapacitor Device

Polythiophene (PT) thin films have been prepared by chemical bath deposition (CBD) method at room temperature (300 K) via oxidative polymerization of thiophene using ammonium peroxodisulfate (APS) as an oxidizing agent. Globular particulates of PT are deposited on the stainless steel and glass substrates. The morphology and chain structure of PT are studied using scanning electron microscopy (SEM) and Raman spectroscopy techniques, respectively. The electrochemical behavior of PT electrode is studied using cyclic voltammetry and galvanostatic charge? discharge studies. PT thin film shows maximum specific capacitance of 300 F g^?1 at 5 mV s^?1 in 0.1 M LiClO₄/PC electrolyte. The asymmetric device formed with PT and graphite shows supercapacitive properties useful in the power applications.     

Characterization of graphite–polyurethane composite electrodes modified with organofunctionalized SBA-15 nanostructured silica in the presence of heavy metal ions. Application to anodic stripping voltammetry

A graphite–polyurethane composite electrode with Santa Barbara Amorphous 15, SBA-15, mesoporous silica organofunctionalized with 2-benzothiazolethiol (BTSBA) as bulk modifier has been characterized electrochemically by voltammetry and electrochemical impedance spectroscopy (EIS) in the presence of cadmium ions, as an example of a toxic trace heavy metal, as well as by solid-state ¹³C-NMR and by scanning electron microscopy. EIS measurements performed on the modified composite electrodes to investigate the influence of BTSBA on the deposition of cadmium during square wave anodic stripping voltammetry showed that organofunctionalization of the SBA-15 bulk modifier in the composite electrode facilitates heavy metal deposition. Experiments were also carried out with a mixture of submicromolar cadmium, lead, copper and mercury ions and led to similar conclusions.     

Cathodic behavior of graphite in KF-AlF3-based melts with various cryolite ratios

The cathodic behavior of graphite in KF-AlF₃-based melt with various cryolite ratios (CR; molar ratio of KF to AlF₃) were investigated by means of cyclic voltammetry, sampled-current voltammetry, and chronopotentiometry. The limiting current of aluminum deposition and critical current density of potassium intercalation on graphite cathode in KF-AlF₃-based melt decreased with the increase of CR of the melt. Lowering the CR of KF-AlF₃-based melt suppressed the potassium intercalation but enhanced the formation of aluminum carbide. In the KF-AlF₃-based melt with CR of 1.0, formation of Al₄C₃ seriously occurred, which resulted not only from the chemical reaction of aluminum and carbon but also from the electrochemical reduction of carbon under higher overpotential. However, both the X-ray diffraction and scanning electron microscopy failed to detect the existence of potassium–graphite intercalation compound and Al₄C₃ in the resultants after galvanostatic electrolysis.     

纳米碳管电极的制备与电化学检测性能研究

纳米碳管由于其独特的物理和化学性能及广阔的应用前景而备受关注,其相关研究涉及到众多领域[1￣3]。在电化学分析领域,与其它碳电极材料相比,纳米碳管电极具有较大的电极表面积和较高的电子传递速率,其使用能增大响应电流、降低检出限,是目前电化学分析电极中一个十分引人注目     

An azamacrocyclic electrolyte additive to suppress metal deposition in lithium-ion batteries

An azamacrocyclic compound (1,4,8,11-tetraazacyclotetradecane, cyclam), which forms strong chelate complexes with metal ions such as Mn(II) and Fe(II), is tested as an electrolyte additive to suppress metal deposition. The tetradentate cyclic ligand is electrochemically stable within the working voltage of lithium-ion batteries (0.0–4.5 V vs. Li/Li⁺), hence it is practicable as an electrolyte additive. Deposition of Mn on a graphite electrode, which is severe when a Li/graphite cell is cycled in a Mn(II)-containing electrolyte solution, is greatly suppressed by adding cyclam. Our elemental analysis reveals negligible Mn deposits on a graphite electrode indicating the beneficial role of cyclam. The suppression of metal deposition is further indicated by the absence of an internal short between Li metal and lithium cobalt oxide positive electrode.