Electrocatalytic oxidation of methanol and ethanol at carbon ceramic electrode modified with platinum nanoparticles

The use of carbon ceramic electrode (CCE) modified with platinum particles was studied for the electrocatalytic oxidation of methanol and ethanol by cyclic voltammetry and chronoamperometry. After preparation of a carbon ceramic as an electrode matrix by sol–gel technique, its surface was potentiostatically coated with Pt nanoparticles at −0.2 V vs. SCE in an aqueous solution of 0.1 M H₂SO₄ containing 0.002 M H₂PtCl₆. The electrocatalyst was characterized by XRD, SEM and cyclic voltammetry. The effective parameters on electrocatalytic oxidation of the alcohols, i.e. the amount Pt loadings, medium temperature and working potential limit in anodic direction were investigated and the results were discussed. This modified electrode showed an enhanced current density over the other Pt-modified electrodes making it more attractive for fuel cell applications.     

Improvement of thermal stability of NO oxidation Pt/Al2O3 catalyst by addition of Pd

The present work has been undertaken to tailor Pt/Al₂O₃ catalysts active for NO oxidation even after severe heat treatments in air. For this purpose, the addition of Pd has been attempted, which is less active for this reaction but can effectively suppress thermal sintering of the active metal Pt. Various Pd-modified Pt/Al₂O₃ catalysts were prepared, subjected to heat treatments in air at 800 and 830 °C, and then applied for NO oxidation at 300 °C. The total NO oxidation activity was shown to be significantly enhanced by the addition of Pd, depending on the amount of Pd added. The Pd-modified catalysts are active even after the severe heat treatment at 830 °C for a long time of 60 h. The optimized Pd-modified Pt/Al₂O₃ catalyst can show a maximum activity limited by chemical equilibrium under the conditions used. The bulk structures of supported noble metal particles were examined by XRD and their surface properties by CO chemisorption and EDX-TEM. From these characterization results as well as the reaction ones, the size of individual metal particles, the chemical composition of their surfaces, and the overall TOF value were determined for discussing possible reasons for the improvement of the thermal stability and the enhanced catalytic activity of Pt/Al₂O₃ catalysts by the Pd addition. The Pd-modified Pt/Al₂O₃ catalysts should be a promising one for NO oxidation of practical interest.     

Electrochemical Reduction of Oxygen on Carbon Supported Pt and Pt/Ru Fuel Cell Electrodes in Alkaline Solutions

A study of O₂ reduction in 1 M NaOH solution at gas diffusion electrodes made from carbon supported Pt and Pt/Ru catalysts is reported. Two Tafel regions were observed for both the Pt and Pt/Ru electrodes. Although the same mechanism was suggested for oxygen reduction on both Pt and Pt/Ru catalysts, the O₂ reduction activity was lower on Ru. Electrochemical Impedance Spectroscopy (EIS) analysis was carried out at different potentials and showed the significant contribution of diffusion on the reaction process and kinetics. The effect of methanol on O₂ reduction was investigated in solutions containing various concentrations of methanol. The electrode performance deteriorated with increasing methanol concentration because of a mixed cathode potential. The methanol tolerance, i. e., the methanol concentration which polarises the O₂ reduction reaction for O₂ reduction, at the Pt/C electrode with a Pt loading of 1.2 mg cm^–2 is 0.2 M methanol in 1 M NaOH.     

Effect of electrode materials on the kinetics of the electro-reduction of peroxyacetic acid

Electrochemical behavior of peroxyacetic acid (PAA) and hydrogen peroxide (H₂O₂) was examined at various metal and carbon electrodes (i.e., Au, Ag, Cu, Pt, Pd, Rh, Ti, W, Hg, Ni, Fe, glassy carbon (GC), and basal-plane pyrolytic graphite (BPG)) in 0.1 M acetate buffer solution (pH 5.5) using potentiostatic (i.e., cyclic voltammetry and rotating disk electrode voltammetry) and galvanostatic techniques. It was found that the electro-reductions of PAA and H₂O₂ are highly sensitive to electrode material. Both species were found to be electrochemically and separately reduced at Au, Ag, Cu, Pt, Pd, GC, and BPG electrodes. On the other hand, at Fe, Ni, Hg, Rh, Ti, and W electrodes, voltammetric response for the PAA reduction was not obviously observed. The kinetics of electro-reduction of PAA in 0.1 M acetate buffer solution was studied at Au, Ag, and GC electrodes in details, and the relevant kinetic parameters (i.e., the exchange current density, j₀, the standard rate constant, k⁰, and cathodic transfer coefficient, α_c) were estimated from the Tafel plots. The cyclic voltammetric reduction peak potentials obtained for the PAA reduction at Au, Ag, and GC electrodes were compared with those calculated using the kinetic and thermodynamic parameters obtained under the same experimental conditions. The measured and calculated reduction peak potentials at each electrode were found to be in agreement with each other, indicating that the evaluated values of kinetic parameters for the reduction of PAA at Au, Ag, and GC electrodes are reasonable.     

Direct Electrochemistry and Electrocatalysis of Hemoglobin on Bimetallic Au–Pt Inorganic–Organic Nanofiber Hybrid Nanocomposite and Mesoporous Molecular Sieve MCM-41

A glassy carbon electrode modified with MCM-41 and bimetallic inorganic–organic nanofiber hybrid nanocomposite was prepared and used for determination of trace levels of hydrogen peroxide (H₂O₂). The direct electron transfer (DET) and electrocatalysis of hemoglobin (Hb) entrapped in the MCM-41 modified Au–Pt inorganic–organic nanofiber hybrid nanocomposite electrode (Au–PtNP/NF/GCE) were investigated by using cyclic voltammetry in 0.1 M pH 7.0 phosphate buffer solution. Due to its uniform pore structure, high surface area and good biocompatibility, the mesoporous silica sieve MCM-41 provided a suitable matrix for immobilization of biomolecules. The MCM-41 modified Au–Pt inorganic–organic nanofiber hybrid nanocomposite electrode showed significant promotion to DET of Hb, which exhibited a pair of well-defined and quasi-reversible peaks for heme Fe(III)/Fe(II) with a formal potential of ?0.535 V (vs. Ag/AgCl). Additionally, the Hb immobilized on the MCM-41 modified electrode showed excellent electrocatalytic activity toward H₂O₂ reduction.     

Development of nonenzymatic hydrogen peroxide sensor based on catalytic properties of copper nanoparticles/Rutin/MWCNTs/IL/Chit

A new electrochemical sensor based on copper nanoparticles for detection of hydrogen peroxide has been developed. Copper nanoparticles/Rutin/Multiwall Carbon Nanotubes/Ionic liquid/Chitosan modified glassy carbon electrode (CuNPs/Rutin/MWCNTs/IL/Chit/GCE) prepared by consecutive coating of MWCNTs/IL/Chit nanocomposite and rutin on the GCE, followed by the electrodeposition of copper. Surface physical characteristics of modified electrode were studied by scanning electron microscopy (SEM). The electrochemical performance of the sensor for detection of H₂O₂ was investigated by cyclic voltammetry and chronoamperometry techniques. The modified electrode exhibits an enhanced electrocatalytic property, low working potential, high sensitivity, excellent selectivity, good stability, and fast amperometric sensing towards reduction of hydrogen peroxide. The response to H₂O₂ is linear in the range between 0.35 μM to 2500 μM, and the detection limit is 0.11 μM.     

Effect of microstructure on the electrochemical behavior of Pt/YSZ electrodes

Two types of O₂,Pt/YSZ electrode preparation (Pt/YSZ cermet and sputtered platinum film) have been characterized by SEM and by cyclic voltammetry and chronoamperometry at 450 °C in 20 kPa oxygen. Cyclic voltammetry on the cermet and on the as-sputtered non-porous film electrode evidenced the characteristics of the PtO _x /Pt couple. The corresponding redox reaction occurs at the metal/electrolyte interface and it manifests itself by an anodic wave and one of more cathodic peaks in the voltammogram. Heat treatment of the sputtered electrode at 700 °C in oxygen atmosphere resulted in a porous structure by coalescence of the film. Cyclic voltammetry of the porous film electrode featured the characteristics of the O₂/O²⁻ couple, i.e. the redox reaction of gaseous oxygen occurring at the tpb. Chronoamperometry at anodic potentials showed similar features for both electrode preparations: an initial inhibition, a current peak and a slow activation, the latter being related to the phenomenon of electrochemical promotion of catalysis.     

Electrochemical behavior and its electrocatalytic properties of chemically modified electrode with Keggin-type [SiNi(H2O)W11O39]

A monolayer of Keggin-type heteropolyanion [SiNi(H₂O)W₁₁O₃₉]⁶⁻ was fabricated by electrodepositing [SiNi(H₂O)W₁₁O₃₉]⁶⁻ on cysteamine modified gold electrode. The monolayer of [SiNi(H₂O)W₁₁O₃₉]⁶⁻ modified gold electrode was characterized by atomic force microscopy (AFM) and electrochemical method. AFM results showed the [SiNi(H₂O)W₁₁O₃₉]⁶⁻ uniformly deposited on the electrode surface and formed a porous monolayer. Cyclic voltammetry exhibited one oxidation peak and two reduction peaks in 1.0 M H₂SO₄ in the potential range of −0.2 to 0.7 V. The constructed electrode could exist in a large pH (0-7.6) range and showed good catalytic activity towards the reduction of bromate anion (BrO₃⁻) and nitrite (NO₂⁻), and oxidation of ascorbic acid (AA) in acidic solution. The well catalytic active of the electrode was ascribed to the porous structure of the [SiNi(H₂O)W₁₁O₃₉]6⁻ monolayer.     

Electrochemical study on the inhibitory effect of the underpotential deposition of zinc on Zn-Co alloy electrodeposition

Zn-Co alloy electrodeposition from chloride baths containing different Zn²⁺/Co²⁺ ratios was investigated by cyclic voltammetry and anodic linear sweep voltammetry using a Pt electrode. The peaks were attributed by means of EDX analysis, SEM and TEM observations performed on some alloys potentiostatically deposited. In the range of potential where zinc deposits underpotential, cyclic voltammetry showed a complex cathodic peak with one maximum and two shoulders, correlated with the deposition of different cobalt rich alloys. Up to four anodic peaks, two correlated with zinc oxidation from η and γ phases and two correlated with oxidation of solid solutions of zinc in cobalt, were observed. ALSV and TEM indicated that the remarkable increase in Zn content of the alloy, which occurs with a strong inhibition of the process at potentials more negative than that of the cathodic peak and more positive than the bulk deposition potential of zinc, is due to the deposition of γ phase. No inhibition of the alloy deposition process was observed with very low concentrations of zinc (<0.015 M) in the bath containing 0.19 M Co²⁺.     

Effects of poly-1,5-diaminoanthraquinone morphology on oxygen reduction in acidic solution

The poly-1,5-diaminoanthraquinone (P15DAAQ) modified Pt electrodes show electrocatalytic activity for oxygen reduction reaction (ORR) with oxygen reduction peak at about 0.39 V in 0.1 M H₂SO₄. The P15DAAQ with different thickness has different morphology. The effects of morphologies on the electrocatalytic behaviors of P15DAAQ for oxygen reduction reaction are investigated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) measurements. We propose two different O₂-transport processes on electrodes modified with thin P15DAAQ and thick P15DAAQ. Together with the quantitative analysis with O₂-transport dynamics, electron-transfer resistance, and catalytic reaction rate during ORR, thin P15DAAQ electrode performs better electrocatalysis for ORR, although thick P15DAAQ provides higher real surface area and more reactive sites which is beneficial for ORR within a short time.     

Catalytic activity of dual catalysts system based on nano-manganese oxide and cobalt octacyanophthalocyanine toward four-electron reduction of oxygen in alkaline media

The electrocatalysis of the dual functional catalysts system composed of electrolytic nano-manganese oxide (nano-MnOx) and cobalt octacyanophthalocyanine (CoPcCN) toward 4-electron reduction of oxygen (O₂) in alkaline media was studied. Nano-MnOx electrodeposited on the CoPcCN monolayer-modified glassy carbon (GC) electrode was clarified as the nano-rods with ca. 10-20 nm diameter by scanning electron microscopy. The peak current for O₂ reduction at the dual catalysts-modified GC electrode increases largely and the peak potential shifts by ca. 160 mV to the positive direction in cyclic voltammograms compared with those obtained at the bare GC electrode. The Koutecký-Levich plots indicate that the O₂ reduction at the dual catalysts-modified GC electrode is an apparent 4-electron process. Collection efficiencies obtained at the dual catalysts-modified GC electrode are much lower than those at the GC electrode and are almost similar to those at the Pt nano-particles modified GC electrode. The obtained results demonstrate that the dual catalysts system possesses a bifuctional catalytic activity for redox-mediating 2-electron reduction of O₂ to HO₂⁻ by CoPcCN as well as catalyzing the disproportionation of HO₂⁻ to OH⁻ and O₂ by nano-MnOx, and enables an apparent 4-electron reduction of O₂ at a relatively low overpotential in alkaline media. In addition, it has been found that the cleaning of the dual catalysts-modified electrode by soaking in 0.1 M sulfuric acid solution enhances its catalytic activity toward the reduction of O₂.     

Hydrodynamic voltammetric studies of the oxygen reduction at gold nanoparticles-electrodeposited gold electrodes

The electrocatalytic reduction of oxygen at Au nanoparticles-electrodeposited Au electrodes has been studied using rotating disk electrode (RDE) voltammetry in 0.5 M H₂SO₄. Upon analyzing and comparison of the limiting currents data obtained at various rotation speeds of this RDE with those obtained at the bulk Au electrode, an effective value of the number of electrons, n, involved in the electrochemical reduction of O₂ was estimated to be ca. 4 for the former electrode and ca. 3 for the bulk Au electrode at the same potential of −350 mV versus Ag/AgCl/KCl(sat.). This indicates the higher possibility of further reduction and decomposition of H₂O₂ at Au nanoparticles-electrodeposited Au electrode in this acidic medium. The reductive desorption of the self-assembled monolayer of cysteine, which was formed on the Au nanoparticles-electrodeposited Au electrode, was used to monitor the change of the specific activity of the bulk Au electrode upon the electrodeposition of the Au nanoparticles.     

Preparation of high loading Pt nanoparticles on ordered mesoporous carbon with a controlled Pt size and its effects on oxygen reduction and methanol oxidation reactions

A series of ordered mesoporous carbon (OMC) supported Pt (Pt/OMC) catalysts with a controlled Pt size from 2.7 to 6.7 nm at high Pt loading around 60 wt.% have been prepared and their electrocatalytic activities for the electrode reactions relevant to the direct methanol fuel cells have been investigated. The Pt/OMC catalysts with a high dispersion (Pt size around 3 nm) could be prepared by the use of a modified, sequential impregnation–reduction method. The Pt/OMC catalysts containing larger Pt particles were obtained by increasing reduction temperature under hydrogen flow and Pt loading, and by performing impregnation–reduction in a single cycle. The oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activities of Pt/OMC catalysts as a function of Pt size were investigated at room temperature in 0.1 M HClO₄ and (0.1 M HClO₄ + 0.5 M methanol), respectively. The specific activity of Pt/OMC for ORR steeply increased up to 3.3 nm and became independent of Pt size from 3.3 to 6.7 nm, and the mass activity curve exhibited maximum activity at 3.3 nm. The MOR activity of Pt/OMC also exhibited the similar trend with the ORR activity, as the maximum of mass activity was also found at 3.3 nm. The results of the present work indicate that the Pt catalysts of ca. 3 nm is an optimum particle size for both ORR and MOR, and this information may be translated into design of high performance membrane electrode assembly.     

Simultaneous sulfonation and reduction of graphene oxide as highly efficient supports for metal nanocatalysts

The sulfonated reduced graphene oxide (S-rGO) as supports and size-controlled Pt nanoparticles (NPs) for proton exchange membrane fuel cell (PEMFC) catalysts was investigated. The S-rGO was fabricated by a lyophilization-assisted method from a liquid mixture of GO and (NH₄)₂SO₄ with a subsequent thermal treatment in inert gas. Sulfonic acid groups were grafted on GO and a reduction of GO was achieved simultaneously. Transmission electron microscope (TEM) results showed a uniform deposition of Pt NPs on S-rGO (Pt/S-rGO) with a narrow particle size distribution ranging from 2 to 5 nm in diameter. A higher catalytic activity of this novel Pt/S-rGO catalyst was revealed in comparison with that of Pt/GO, Pt/rGO and conventional Pt/C catalysts by cyclic voltammetry and oxygen reduction reaction measurements due to an enhanced triphase boundary. Significantly, the Pt/S-rGO catalyst also presented an excellent electrochemical stability. This new catalyst thus holds a great potential application in PEMFCs in terms of enhanced activity and durability.     

Effect of Co on oxygen reduction reaction catalyzed by Pt catalyst, and its implications for fuel cell contamination

The oxygen reduction reaction (ORR) catalyzed by Pt was studied in the presence of Co²⁺ using cyclic voltammetry (CV), rotating disk electrode (RDE), and rotating ring-disk electrode (RRDE) techniques in an effort to understand fuel cell cathode contamination caused by Co²⁺. Findings indicated that Co²⁺ could weakly adsorb on the Pt surface, resulting in a slight change in ORR exchange current densities. However, this weak adsorption had no significant effect on the nature of the ORR rate determining steps. The results from both RDE and RRDE indicated that the overall electron transfer number of the ORR in the presence of Co²⁺ was reduced, with ∼9% more H₂O₂ being produced. We speculate that the weakly adsorbed Co²⁺ on Pt could react with the H₂O₂ intermediate and form a Co²⁺-H₂O₂ intermediate, inhibiting the further reduction of H₂O₂ and thus resulting in more H₂O₂ production. The fuel cell performance drop observed in the presence of Co²⁺ could be attributed to the reduction in overall electron transfer number and the increase in H₂O₂ production. Higher production could intensify the attack by H₂O₂ and its radicals on membrane electrode assembly components, including the ionomer, carbon support, Pt particles, and membrane, leading to fuel cell degradation.     

The initial stages of palladium deposition onto Pt(1 1 1)

The electrodeposition of Pd onto Pt(1 1 1) from PdCl₂ and PdSO₄ containing solutions was studied by cyclic voltammetry and in situ scanning tunnelling microscopy. Pd deposition starts by forming a pseudomorphic monolayer in both cases. While in the presence of chloride this monolayer is deposited at underpotentials, its formation in chloride-free solution is kinetically hindered to such an extent that the deposition peak is shifted negative of the equilibrium potential. Detailed structure information has been obtained from STM data about the Pd layer as well as the co-adsorbed anions. Bulk deposition from the chloride-containing solution proceeds via a quasi layer-by-layer fashion. However, the particular electrochemical properties of the first Pd monolayer disappear only after deposition of the equivalent of four more Pd layers. The electrochemical behaviour of such films is similar to that of a rough Pd(1 1 1) surface. Pd bulk deposition from chloride-free solution leads to the formation of three-dimensional clusters from the very beginning. About 10 ML equivalents are needed in that case to completely cover the first Pd monolayer.     

Electrocatalytic reduction of hydrogen peroxide at nanostructured copper modified electrode

The electrocatalytic reduction of hydrogen peroxide (H₂O₂) has been studied at nanostructured copper (Cu_nano) modified glassy carbon (GC/Cu_nano) electrode in phosphate buffer (pH 7.2). The electrical properties of GC/Cu_nano modified electrodes were studied by electrochemical impedance spectroscopy (EIS). Surface and electrochemical characterization were carried out by using atomic force microscopy (AFM) and cyclic voltammetry. A well-defined H₂O₂ reduction signal, which is due to mediation of a surface active site redox transition exhibits at the GC/Cu_nano electrode. The Cu_nano is acting as a bridge without the aid of any other electron mediator, which enables the direct electron transfer between the modified electrode and the substrate. The results are compared with bulk copper macroelectrode and emphasized the efficiency of the Cu_nano modified electrode. Systematic investigations were made to optimize the experimental parameter, such as applied potential (E_app) for copper electrodeposition. The calibration curve obtained from chronoamperometric studies was found to be linear in the range 0.5 to 8.0 μM H₂O₂ with a detection limit of ca.10 nM (S/N = 3) at the GC/Cu_nano electrode. The modified electrode is stable for 1 week in phosphate buffer after repetitive measurements.     

Co3O4-chitosan/biomass-derived porous carbon molecularly imprinted polymer integrated electrode for selective detection of glucose

The detection of glucose (Glu) is of great significance in medical diagnosis, food processing and biotechnology. Rapid, accurate and convenient detection technology is particularly important. Herein, the Co₃O₄-PC nanocomposite grown on biomass-derived porous carbon (PC) was prepared by hydrothermal method and subsequent air calcination. Chitosan (CS) was electrodeposited on the surface of Co₃O₄-PC by potentiostatic deposition with Glu as the template molecule. Finally, the template molecule was eluted by cyclic voltammetry to create specific recognition sites for Glu, and a highly selective and stable Glu sensor was constructed. The obtained MIP (molecularly imprinted polymer)-Glu-CS/Co₃O₄/PC nanocomposites were characterized by scanning electron microscopy, Raman spectroscopy, cyclic voltammetry, chronoamperometry and so on. The results showed that the MIP-Glu-CS/Co₃O₄-PC had great catalytic performance for Glu detection with a linear range of 12.17 μM-2.3 mM, a detection limit of 4.01 μM, and a sensitivity of 407.5 μA cm^?2 mM^?1. The sensor has excellent selectivity and stability. This work provides a guide for improving the selectivity of nanozymes.     

Study of IrxRu1−xO2 oxides as anodic electrocatalysts for solid polymer electrolyte water electrolysis

Electrocatalysts of the general formula Ir_xRu_1−xO₂ were prepared using Adams’ fusion method. The crystallite characterization was examined via XRD, and the electrochemical properties were examined via cyclic voltammetry (CV) in, linear sweep voltammetry (LSV) and chronopotentiometry measurements in 0.5 M H₂SO₄. The electrocatalysts were applied to a membrane electrode assembly (MEA) and studied in situ in an electrolysis cell through electrochemical impedance spectroscopy (EIS) and stationary current density–potential relations were investigated. The Ir_xRu_1−xO₂ (x = 0.2, 0.4, 0.6) compounds were found to be more active than pure IrO₂ and more stable than pure RuO₂. The most active electrocatalyst obtained had a composition of Ir_0.2Ru_0.8O₂. With an Ir_0.2Ru_0.8O₂ anode, a 28.4% Pt/C cathode and the total noble metal loading of 1.7 mg cm⁻², the potential of water electrolysis was 1.622 V at 1 A cm⁻² and 80 °C.     

Voltammetric behavior and the determination of quercetin at a flowerlike Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles modified glassy carbon electrode

Flowerlike Co₃O₄ nanoparticles were used as a modifier on the glassy carbon electrode to fabricate a quercetin (Qu) sensor. The morphology and crystallinity of the prepared Co₃O₄ material were investigated by scanning electron microscopy and X-ray diffraction. Electrochemical behavior of Qu at the sensor was studied by cyclic voltammetry and semi-derivative voltammetry. Results suggested that the modified electrode exhibited a strong electrocatalytic activity toward the redox of Qu. The electron transfer coefficient (α), the number of electron transfer (n), and the diffusion coefficient (D) of Qu at the sensor were calculated. Under the optimum conditions, the catalytic peak currents of Qu were linearly dependent on the concentrations of Qu in the range from 5.0 × 10⁻⁷ to 3.3 × 10⁻⁴ M, with a detection limit of 1.0 × 10⁻⁷ M. This proposed method was successfully applied to determine the quercetin concentration in Ginkgo leaf tablet and human urine samples.