Application of phosphotungstic acid–nickel composite-modified carbon paste electrode for electrocatalytic oxidation of methanol in alkaline solution

Phosphotungstic acid (PWA) was used for accumulation of nickel ions at the carbon paste electrode for preparation of PWA-modified CPE (PWA/CPE). The PWA was evenly mixed with graphite powder and paraffin oil. Then, for preparation of Ni/PWA/CPE, Ni ions were included onto the PWA/CPE surface through immersion method at open circuit condition. The scanning electron microscopy (SEM), energy-dispersive spectroscopy and electrochemical methods were used to verify the prepared electrodes. The SEM images reveal that morphology of the CPE was influenced by PWA addition. Application of the Ni/PWA/CPE for methanol oxidation was explored by various electrochemical techniques. Electrochemical response of methanol oxidation at the surface of Ni/PWA/CPE was 2.5 times higher than that Ni/CPE. The obtained results indicated that the modified electrode exhibited high electrocatalytic activity toward methanol oxidation. Then, catalytic rate constant was found to be 8.25 × 10⁴ cm³ mol ^?1 s^?1 using chronoamperometry method. Furthermore, the effects of several parameters, such as PWA loading, NiSO₄ concentration, accumulation time and methanol concentration toward methanol oxidation at the surface of this modified electrode as well as stability, have been investigated.     

Electrocatalytic oxidation of methanol and other short chain aliphatic alcohols at Ni(II)–quercetin complex modified multi-wall carbon nanotube paste electrode

A modified electrode Ni(II)–Qu–MWCNT-PE has been fabricated by electrodepositing nickel(II)–quercetin [Ni(II)–Qu] complex on the surface of multi-wall carbon nanotube paste electrode (MWCNT-PE) in alkaline solution. Ni(II)–Qu–MWCNT-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)–MWCNT-PE and Ni(II)–Qu-carbon paste electrode. It also shows electrocatalytic activity toward the oxidation of methanol and other short chain aliphatic alcohols, such as ethanol, 1-propanol, and 1-butanol. The catalytic peak current and peak potential decrease in exponential form with the increase of carbon number of the chains. Kinetic parameters such as the electron transfer coefficient, α, rate constant, k _s, of the electrode reaction, and the catalytic rate constant, k _cat, for oxidation of methanol are determined. The stability and reproducibility of the Ni(II)–Qu–MWCNT-PE are good for practical applications.     

Bimetallic Cu–Pt/nanoporous carbon composite as an efficient catalyst for methanol oxidation

A novel bimetallic Cu–Pt nanoparticle supported onto Cu/indirectly carbonized nanoporous carbon composite (Cu–Pt/ICNPCC) was prepared through a two-step process: first, carbonization of furfuryl alcohol-infiltrated MOF-199 [metal–organic framework Cu₃(BTC)₂ (BTC?=?1,3,5-benzene tricarboxylate)], without removing the Cu metal with HF aqueous solution; second, the partial galvanic replacement reaction (GRR) of Cu nanoparticles by Pt^IV upon immersion in a platinum(IV) chloride solution. The synthesized materials characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), and electrochemical methods. The EDS result revealed that part of Cu nanoparticles have been substituted by Pt nanoparticles after GRR. The methanol oxidation at the surface of Cu–Pt/ICNPCC was investigated by cyclic voltammetry method in 0.5 M H₂SO₄ and indicated good electro-catalytic activity towards methanol oxidation (E_p?=?0.85 V vs. NHE and j_f?=?1.00 mA cm^?2). It is suggested that this improvement is attributed to the effect of proper Cu/ICNPCC for fine dispersion, efficient adhesion, and prevention of Pt coalescing.     

A study of the electrocatalytic oxidation of methanol on a nickel–salophen-modified glassy carbon electrode

Nickel–salophen-modified glassy carbon electrodes prepared by transferring one drop of Ni–salophen complex solution on the electrode surface. This modified electrode has been used for the electrocatalytic oxidation of methanol in alkaline solutions with various methods such as cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The electrooxidation was observed as large anodic peaks, and early stages of the cathodic direction of potential sweep around 20 mV vs. Ag|AgCl|KCl_sat. A mechanism based on the electrochemical generation of Ni (Ш) active sites and their subsequent consumptions by methanol have been discussed. EIS studies were employed to unveil the charge transfer rate as well as the electrical characteristics of the catalytic surface. For the electrochemical oxidation of methanol at 5.0 M concentration, charge transfer resistance of nearly 0.936 kΩ was obtained, while the resistance of the electrocatalyst layer was about 111.6 Ω.     

Co@Pt–Ru core-shell nanoparticles supported on multiwalled carbon nanotube for methanol oxidation

A novel synthesis route concerning reduction of cobalt core onto the surface of multiwalled carbon nanotubes (MWCNTs) and then substitution of part of Co core with Pt–Ru precursor was developed to synthesize the core-shell Co@Pt–Ru/MWCNTs catalyst. In this synthesis route, sodium borohydride and hydrazine hydrate were employed to reduce cobalt step by step in order to control the size of cobalt and the growth speed of cobalt crystal. The novel core-shell Co@Pt–Ru/MWCNTs catalyst shows good electrocatalysis towards methanol oxidation.     

Platinum nanoparticles supported on zirconia–carbon black nanocomposites for methanol oxidation reaction

Platinum (Pt) nanoparticles supported on zirconia–carbon black nanocomposites (Zr–C), which annealed at different temperatures, used as Pt/Zr–C electrocatalysts for methanol oxidation reaction (MOR) are prepared and characterized in this study. Transmission electron microscope images and X-ray diffraction analysis showed that the diameters of Pt nanoparticles are around 3–4 nm. Electrocatalytic MOR performances of these Pt/Zr–C electrocatalysts are investigated by cyclic voltammetry, CO-stripping voltammetry, and chronoamperometry. All the Pt/Zr–C electrocatalysts synthesized in this study exhibited higher MOR efficiency than that of the commercial E-TEK Pt/C electrocatalyst, and the electrocatalyst using Zr–C support annealed at 300 °C, achieving the highest MOR efficiency among all the electrocatalysts.     

Non-enzymatic sensing of uric acid using a carbon nanotube ionic-liquid paste electrode modified with poly(β-cyclodextrin)

We describe a nonenzymatic electrochemical sensor for uric acid. It is based on a carbon nanotube ionic-liquid paste electrode modified with poly(β-cyclodextrin) that was prepared in-situ by electropolymerization. The functionalized multi-walled carbon nanotubes and the surface morphology of the modified electrodes were characterized by transmission electronic microscopy and scanning electron microscopy. The electrochemical response of uric acid was studied by cyclic voltammetry and linear sweep voltammetry. The effects of scan rate, pH value, electropolymerization cycles and accumulation time were also studied. Under optimized experimental conditions and at a working voltage of 500 mV vs. Ag/AgCl (3 M KCl), response to uric acid is linear in the 0.6 to 400 μΜ and in the 0.4 to 1 mΜ concentration ranges, and the detection limit is 0.3 μΜ (at an S/N of 3). The electrode was successfully applied to the detection of uric acid in (spiked) human urine samples.

SEM images of (a) carbon ionic liquid electrode (CILE) (b) MWNT-CILE (c) β-CD/CILE (d) β-CD/ MWNT-CILE. The surfaces of carbon ionic liquid electrode (CILE) (a) and MWNT-CILE (b) were homogenous and no separated carbon layers can be observed; After β- cyclodextrin (CD) was modified on CILE and MWNT-CILE, the surfaces of β-CD modified electrodes (c and d) exhibited loose and porous morphologies.

     

Copper oxide-modified glassy carbon electrode prepared through copper hexacyanoferrate–G5-PAMAM dendrimer templates as electrocatalyst for carbohydrate and alcohol oxidation

We describe the modification of a glassy carbon electrode by electro-deposition of copper hexacyanoferrate (CuHCF) in the presence of an amine-terminated dendrimer (PAMAM) as a template. The electrode containing the CuHCF template was cycled in alkaline solution to generate a layer of cupric oxide (CuO). The mechanism of the formation of CuO and its electrocatalytic activity were investigated by cyclic voltammetry. Scanning electron microscopy reveals that the CuO prepared by this method has a meso-porous grid-like appearance. The formation of CuO was identified by XPS analysis of the modified electrode. The ability of the CuHCF film towards the electrocatalytic oxidation of carbohydrates and alcohols was detected using cyclic voltammetry. The over-potential required for carbohydrate and alcohol oxidation is lowered by ~400 mV compared to other chemically modified electrodes reported in the literature. Simple methodology has been adopted in this work for the preparation of the catalytically active electrode, and this work also explains the structure directing effect of dendrimer and its influence on the electrocatalytic oxidation of analytes.     

Pt–Ni alloy nanoparticles supported on multiwalled carbon nanotubes for methanol oxidation in alkaline media

The Pt–Ni alloy nanoparticles with different Pt/Ni atomic ratios supported on functionalized multiwalled carbon nanotubes surface were synthesized via an impregnation-reduction method. The nanocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques. XRD demonstrated that Pt was alloyed with Ni. TEM showed that the Pt–Ni alloy nanoparticles were uniformly dispersed on the multiwalled carbon nanotubes (MWCNTs) surface, indicating appropriate amount of Ni in Pt–Ni alloy which facilitates the dispersion of nanoparticles on the MWCNT surface. XPS revealed that the Pt 4f peak in Pt–Ni/MWCNT (4:1) catalyst shifted to a lower binding energy compared with Pt/MWCNT catalyst, and nickel oxides/hydroxides such as NiO, Ni(OH)₂, and NiOOH were on the surface of Pt–Ni nanoparticles. Electrochemical data based on cyclic voltammetry and chronoamperometric curves indicated that Pt–Ni (4:1) alloy nanoparticles exhibited distinctly higher activity and better stability than those of Pt/MWCNTs toward methanol oxidation in alkaline media.     

Amplified oxadiazole derivative nano MgO–multiwall carbon nanotubes modified carbon paste electrode for the determination of dopamine in presence of morphine

In this paper, we report the fabrication of an amplified sensor to determine dopamine in the presence of morphine based on nano-MgO, multiwall carbon nanotubes, and an oxadiazole derivative. The electrochemical behavior and electrocatalyic activity of the sensor toward the oxidation of dopamine were investigated. Cyclic voltammetry was used to study the redox features of the sensor, and the results have shown that dopamine overpotential oxidation at the surface of the sensor was reduced to nearly 460 mV. The diffusion coefficient was estimated by chronoamperometry. Three segmented linear dynamic ranges over the range 0.05–5175.0 and detection limit of 0.021 μM for the quantification of dopamine were obtained using differential pulse voltammetry (DPV). The modified nanocomposite carbon paste electrode, which showed excellent sensitivity, selectivity, repeatability, and reproducibility, was satisfactorily employed to determine dopamine and morphine in actual samples.     

A facile chemical reduction method for synthesis of platinum–iron catalysts on carbon fiber papers for methanol oxidation

To enhance catalytic activity and durability for methanol oxidation reaction (MOR), we have fabricated bimetallic Pt–Fe catalysts on carbon fiber papers (denoted as Pt–Fe@CFP) by a facile chemical reduction method using iron as the precursor, ascorbic acid and sodium hypophosphite as the reductants, respectively. When ascorbic acid is using as the reductant, the Pt–Fe@CFP catalysts are composed of platinum and disordered Pt–Fe phases. The atomic ratio between Pt and Fe can be adjusted by altering deposition conditions. The Pt–Fe@CFP catalysts with Pt/Fe ratio of 1.1, which deposited with surfactant CTAB in bath at room temperature, exhibit excellent catalytic activity and stability in MOR. However, when sodium hypophosphite is employed as the reductant, the co-deposition of phosphorus would lead to a decreased catalytic performance in MOR.     

Platinum–polytyramine composite material with improved performances for methanol oxidation

Polytyramine (PTy) is shown to be a possible alternative to other conducting polymers as a support material for fuel cell electrocatalysts such as platinum. In this work, a Pt–PTy composite was prepared via potentiodynamic deposition of polytyramine on graphite substrate, followed by the electrochemical deposition of Pt nanoparticles. The material obtained by this straightforward method exhibited, for platinum loadings as low as ca. 0.12 mg cm⁻², a specific electrochemically active surface area of the electrocatalyst of ca. 54 m² g⁻¹, together with a good electrocatalytic activity for methanol oxidation in acidic media, thus ensuring better efficiency of Pt utilization. The system Pt–PTy appears to be worthy of development for methanol fuel cell applications also because the results suggested that, when deposited as small particles in a PTy matrix, platinum is less sensitive to fouling during CH₃OH oxidation.     

Molecular simulation of an amorphous poly(methyl methacrylate)–poly(tetrafluoroethylene) interface

Molecular dynamics calculations of an amorphous interfacial system of poly(methyl methacrylate) (PMMA) and poly(tetrafluoroethylene) (PTFE) containing about 10,000 interaction sites were performed for 15 ns under constant pressure and constant temperature conditions. The time evolutions of the thickness, density and number of atomic pairs in the interfaces suggested that the interfaces reached their equilibrium states with an interfacial thickness of about 2 nm at 500 K. The molecular motion in the interface and bulk was compared using mean square displacement and torsional autocorrelation function. The separation at a PMMA/PTFE interface was mimicked using non-equilibrium molecular dynamics calculations by applying the potential energy to the MD cell in a direction perpendicular to the interface. Initially, the PTFE layer close to the interface was deformed, and before complete separation, some segments of the PTFE molecules extended from the bulk to the surface of the PMMA layer, which were attached by the intermolecular interaction. The remaining PTFE molecules were entangled in the bulk, which probably prevented the transfer of the PTFE molecules to the surfaces of the PMMA layers. On the other hand, the PMMA layer was only slightly deformed. This separation behavior can be explained by taking into account the intermolecular interaction, the barrier to the conformational changes of the backbones and the entanglement of the PTFE molecules in the bulk.     

Geopolymer cement–modified carbon paste electrode: application to electroanalysis of traces of lead(II) ions in aqueous solution

Journal of Solid State Electrochemistry - Pb2+ ions were detected on a carbon paste electrode modified with a geopolymer cement. The X-ray pattern and the infrared spectrum of the geopolymer...     

Electrogeneration and characterization of a poly(pyrrole–nickel (II) chlorin) electrode

We describe herein, the electrochemical properties of an hydroporphyrin of Ni(II) substituted by two pyrrole groups in organic media (THF and CH₂Cl₂). In the anodic region it has been shown that the electrochemical behaviour of this complex investigated by cyclic voltammetry and coulometry coupled with UV–visible spectroscopy is strongly dependent on the nature of the solvent.Furthermore, the electrochemical oxidation of the pyrrrole groups has led to the first example of an electrogenerated polypyrrole–metallochlorin film. The resulting modified electrodes exhibit the same electrochemical properties as the monomer free in solution. Preliminary experiments have also demonstrated the possibility to study electrochemically this polymeric film in CH₃CN contrary to the Ni(II) chlorin, which is insoluble in this medium.     

CuO-nanoparticles modified carbon paste electrode for square wave voltammetric determination of lidocaine: Comparing classical and Box–Behnken optimization methodologies

In this research, copper oxide nanoparticles modified carbon paste electrode was developed for the voltammetric determination of lidocaine. The square wave voltammogram of lidocaine solution showed a well-defined peak between +0.5 and +1.5 V. Instrumental and chemical parameters influencing voltammetric response were optimized by both one at a time and Box–Behnken model of response surface methodology. The results revealed that there was no significant difference between two methods of optimization. The linear range was 1–2500 μmol L~(-1)(Ip= 0.11 C_(LH)+ 17.38, R~2= 0.999). The LOD and LOQ based on three and ten times of the signal to noise(S/N) were 0.39 and 1.3 μmol L~(-1)(n = 10),respectively. The precision of the method was assessed for 10 replicate square wave voltammetry(SWV)determinations each of 0.05, 0.5 and 1 μmol L~(-1) of lidocaine showing relative standard deviations 4.1%,3.7% and 2.1%, respectively. The reliability of the proposed method was established by application of the method for the determination of lidocaine in two pharmaceutical preparations, namely injection and gel.     

Platinum electrode coated with a bentonite–carbon composite as an environmental sensor for detection of lead

A Pt wire coated with a bentonite–carbon composite in a poly(vinyl chloride) membrane was used for detection of lead. The sensor has a Nernstian slope of 29.42±0.50 mV per decade over a wide range of concentration, 1.0×10⁻⁷ to 1.0×10⁻³ mol L⁻¹ Pb(NO₃)₂. The detection limit is 5.0×10⁻⁸ mol L⁻¹ Pb(NO₃)₂ and the electrode is applicable in the pH range 3.0–6.7. It has a response time of approximately 10 s and can be used at least for three months. The electrode has good selectivity relative to nineteen other metal ions. The practical analytical utility of the electrode is demonstrated by measurement of Pb(II) in industrial waste and river water samples.