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The monomeric and polymeric tetra-aminophthalocyane to, cobalt(II) species adsorbed onto graphite electrodes are active in electrocatalytic oxygen reduction. While the monomeric species is unstable, the polymerized species is an effective and stable reduction catalyst over a wide pH range. Both the two-electron reduction of oxygen to hydrogen peroxide and the four-electron reduction of oxygen to water are characterized by cyclic voltammetry, rotating disc and rotating ring-disc studies with appropriate theoretical analysis. Some mechanistic information is obtained. This is the first cobalt phthalocyanine species to provide a four-electron reduction pathway which exists over a wide pH range and is stable. The stability is associated with the polymerization since the monomeric species is not stable.

The surface electrochemical response of the Co^II/Co^I redox process of tetraaminophthalocyaninatocobalt(II) (Co^IITAPc) adsorbed on a graphite electrode, was studied in the pH range of 2–13. In aqueous solution, the Co^IITAPc adsorbed graphite electrode displays very strong electrocatalytic activity toward N₂O reduction to N₂, a process which was examined by cyclic and rotating disk electrode voltammetries. The possible application of this Co^IITAPc modified electrode in N₂O analysis was explored.

The mechanism of the dioxygen interaction with and reduction reaction at iron α,β,γ,δ-tetra(4-pyridyl) porphyrin (FeTPyP) deposited on carbon and silver supporting electrodes was investigated with cyclic voltammetry and FTIR, UV-vis and resonance Raman spectroscopies. Results indicate a strong influence of the ligand upon the reduction electrocatalysis. Spectroelectrochemical results support a two-electron pathway resulting most probably in hydrogen peroxide as the primary reduction product.

The mode of interaction with and the mechanism of the dioxygen reduction reaction at six transition metal α,β,γ,δ-tetra(4-pyridyl)porphyrins (MeTPyPs) deposited on carbon and silver supporting electrodes were investigated with cyclic voltammetry, FTIR and UV-vis spectroscopy and resonance Raman spectroscopy. Results indicate a strong influence of both the ligand and the central metal ion upon the reduction electrocatalysis in terms of electrode overpotentials. Spectroelectrochemical results support a two-electron pathway resulting in hydrogen peroxide as the primary reduction product. A significant influence of the central ion on the vibrational behaviour and the dioxygen reduction mechanism was not found.

We report on the synthesis of cobalt 2,3,9,10,16,17,23,24-octakis(2-ethylhexyloxy)phthalocyanine. This complex, when pre-adsorbed onto graphite electrodes, is active for the electro-oxidation of 2-mercaptoethanol. Its activity is higher than that of cobalt phthalocyanine and cobalt tetrasulfonated phthalocyanine adsorbed on graphite. The voltammetric response of adsorbed cobalt 3,4-octaethylhexyl- oxyphthalocyanine exhibits both Co(II)/Co(I) and Co(III)/Co(II) reversible processes. However, the Co(III)/Co(II) couple shows a pH dependence that is different from that reported for other cobalt phthalocyanine derivatives. The much higher activity of cobalt 3,4-octaethylhexyloxyphthalocyanine compared with cobalt tetrasulfonated phthalocyanine and cobalt phthalocyanine is attributed to the electron-donating ability of the ethylhexyloxy substituents on the periphery of the phthalocyanine ligand.

Herein, we present a comprehensive study on electrochemical hydrazine oxidation using hybrid material, MoS₂-GO (molybdenum disulfide-graphene oxide), as an efficient electrocatalyst fabricated using the simple chemical reduction method. The MoS₂-GO hybrid material adopts a distinctive open flower-like morphology, as demonstrated by field emission scanning electron microscopy (FE-SEM). Asymmetric and uneven distribution is indicated by energy dispersive X-ray spectroscopy (EDS), while UV–Vis investigation displays shifts in peak positions and intensities, signifying the successful formation of the MoS₂-GO composite. Further supporting the composite’s structure, X-ray diffraction (XRD) studies validate the hexagonal arrangement of MoS₂ layers on the graphene oxide (GO) surface. Through a combination of material synthesis, characterizations, and electrochemical analyses, we demonstrate that the MoS₂-GO hybrid exhibits a low overpotential ∼0.2V versus SCE. This outstanding electrocatalytic performance of MoS₂-GO underscores its potential as a promising candidate for various electrochemical applications, especially those involving hydrazine-based reactions. GO was used as the supporter and promoter by improving the synergetic effect between MoS₂ and GO toward the hydrazine oxidation reaction.

In this paper, we first fabricated a nanoPt modified platinum electrode. Then through a simple method, the electrode surface was introduced with a submonolayer of bismuth that acted as an effective promoter. Cyclic voltammetry and other characterizations were employed. The obtained Bi^III/nanoPt/Pt electrode exhibited two greatly increased oxidation peaks at negative and positive potential areas, respectively. The signals were far larger than that of platinum electrode because of the large true surface area of nanoparticles and the catalysis of bismuth adsorbed on platinum. In the presence of bismuth, the platinum active sites could combine with more OH^- from bismuth hydroxyl to form a new active site for the oxidation of glucose. The prepared Bi^III/nanoPt/Pt electrode given high sensitivity and excellent linearship to glucose detection and showed the potential application in the areas of electrocatalysis or electroanalysis.

A new electrochemical technique to detect hydrogen peroxide (H₂O₂) was developed. The Pt nanoparticles and Bi^III were subsequently assembled on agmatine sulfate (AS) modified glassy carbon electrode (GCE) and the prepared GCE–AS-Pt–Bi^III was characterized by scanning electron microscopy (SEM) with result showing that the flower-like nanostructure of Pt–Bi^III was yielded. Compared with Pt nanoparticles, the flower-like nanostructure of Pt–Bi^III greatly enhanced the electrocatalysis of GCE–AS-Pt–Bi^III towards H₂O₂, which is ascribed to more Pt–OH obtained on GCE–AS-Pt–Bi^III surface for the presence of Bi^III. Based on its high electrocatalysis, GCE–AS-Pt–Bi^III was used to determine the content of H₂O₂ in the sample of sheet bean curd with standard addition method. Meantime, its electrocatalytic activity also was studied.

The aim of this work is to synthesize polypyrrole (PPy) films on nonconducting cellulosic substrate and modified by copper oxide particles for use in the nitrate electroreduction process. Firstly, the chemical polymerization of polypyrrole onto cellulosic substrate is conducted by using FeCl₃ as an oxidant and pyrrole as monomer. The thickness and topography of the different PPy films obtained were estimated using a profilometer apparatus. The electrochemical reactivity of the obtained electrodes was tested by voltamperometry technique and electrochemical impedance spectroscopy. Secondly, the modification of the PPy film surface by incorporation of copper oxide particles is conducted by applying a galvanostatic procedure from a CuCl₂ solution. The SEM, EDX and XRD analysis showed the presence of CuO particles in the polymer films with dimensions less than 50 nm. From cyclic voltamperometry experiments, the composite activity for the nitrate electroreduction reaction was evaluated and the peak of nitrate reduction is found to vary linearly with initial nitrate concentration.

We presented here three carbon-nanomaterials-based modified glassy carbon electrodes (GCE) with Ni–Ag nanohybrid nanoparticles (NPs) deposited upon, including single-wall carbon nanotubes (SWCNTs), multi-wall carbon nanotubes (MWCNTs) and the mesoporous carbons (MPCs), and compared their morphology effects on both Ni–Ag deposition quality and electrocatalytic performances toward Glu oxidation. After being deposited with Ni–Ag NPs, a homogenous surface with very small Ni–Ag NPs was obtained for Ni–Ag/SWCNTs/GCE, while heterogeneous, coarse surfaces with obvious embedment with large Ni–Ag particles were observed for both Ni–Ag/MWCNTs/GCE and Ni–Ag/MPC/GCE. All three modified electrodes were well characterized in terms of surface morphology, electron transfer rate, hydrophilicity, interference resistance, stability, electrocatalytic behaviors as well as practicability in real samples, based on which Ni–Ag/SWCNTs/GCE was always proved to be more advantageous over other two composite electrodes. Such advantage of Ni–Ag/SWCNTs/GCE was attributed to its desirable surface morphology good for Ni–Ag deposition and exposure of as many active sites as possible to Glu oxidation, leading to the extraordinary electrocatalytic performance.

In this paper, we report a simple sensing strategy for electrochemical determination of ascorbic acid (AA) using a combination of polypyrrole (PPy) thin film and palladium particles composites deposited onto $n$-doped silicon (Si) substrate. A two-step electrochemical process was employed to synthesize the composite films: At first, PPy film (average thickness 200nm) was electrogenerated on Si substrate from an organic solution of the pyrrole under galvanostatic conditions. Secondly, palladium particles were electrodeposited on PPy/Si surface from a separate solution by chronoamperometry technique. The surface morphology analysis of the obtained composites shows a uniform dispersion of palladium particles onto the polymer matrix and reveals that the electrodeposition time has a significant effect on the amount and size of the incorporated palladium particles. The electrochemical reactivity of the Pd–PPy/Si-modified electrodes towards the oxidation of AA was studied by cyclic voltammetry method in 0.1M, pH 7.0 phosphate buffer solution. The oxidation current was proportional to the concentration of AA in the range of 0.5–10mM with a detection limit of 0.2mM.

The amorphous nickel/carbon microspheres (Ni/C-MSs) were synthesized through dehydration and carbonization of glucose at high temperature and high pressure. The obtained Ni/C-MSs and the Ni/C-800-MSs (calcined at 800${}^{\circ }$C) were thoroughly characterized on morphology, composition and catalytic performance. It is found that the Ni/C-MSs showed good catalytic performance for hydrogen generation from aqueous H₃NBH₃ at room temperature. Urea was oxidized electrocatalytically by Ni/C-800-MSs in alkaline medium, indicating a viable method for wastewater remediation and simultaneous production of valuable hydrogen.

Oxygen evolution reaction (OER) is of great importance in splitting water. However, the sluggish OER kinetics at the anode severely hinders the H₂ evolution at the cathode which is a crucial procedure for energy storage. Herein, we report the synthesis of a new OER catalyst of Co(OH)_x(WO${}_4{)}_y$via a one-step hydrothermal method, where the incorporation of WO${}_4^{2-}$ as a condenser greatly enhanced the electrocatalytic activity of Co(OH)₂ toward OER. Moreover, the introduction of mesoporous carbon (MC) further improves the electrocatalytic performance of Co(OH)_x(WO${}_4{)}_y$ by forming the nanocomposites of Co(OH)_x(WO${}_4{)}_y$/MC. The synergism between Co(OH)₂ and WO${}_4^{2-}$ and the synergistic catalytic effect of Co(OH)_x(WO${}_4{)}_y$ and MC majorly contributed to the apparently enhanced electrocatalysis of Co(OH)_x(WO${}_4{)}_y$/MC toward OER. This work provides an efficient strategy to improve the electrocatalytic activity of Co(OH)₂ by introducing WO${}_4^{2-}$ and forming nanocomposites between Co(OH)_x(WO${}_4{)}_y$ and MC for low-cost, convenient and highly efficient water oxidation.

The Mn oxidation state of two water soluble Mn porphyrins, MnTMPyP and MnTPPS₄, was studied as a function of the aqua or hydroxo ligands of the Mn atom. In NaOH solutions, long-lived O=Mn(IV) species were detected in the presence of O₂. Conversely, the dihydroxo Mn(III) porphyrin reduces spontaneously to the Mn(II) species in the absence of O₂. In alkaline solutions, these Mn porphyrins were able to electrocatalyze the 4-electron reduction of O₂ to H₂O on a vitreous carbon electrode.

The complex N,N',N″,N‴-tetramethyl-tetra-3,4-pyridinoporphyrazinocobalt(II) ([Co^IITMPz[4+])⁴⁺ adsorbed on a graphite electrode undergoes spontaneous reduction, forming a surface containing Co^I. Five reversible surface peaks are observed at low pH, two of which are two-electron concerted processes. At high pH, one of these two-electron processes splits into two one-electron waves. Both oxidation and reduction of the central metal can be observed, along with successive reduction steps involving the porphyrazine ligand. Notable is the marked shift to positive potentials of these processes, relative to unsubstituted cobalt phthalocyanine, due to the positive charge localized on the porphyrazine. The electrocatalytic activity of this complex modified electrode toward the reduction of hydrogen peroxide is also reported. We demonstrate that a series of different surfaces exist which are obtained by variation of pH and polarization potential and that these surfaces possess differing electrocatalytic activity. Surfaces inactive to hydrogen peroxide can exist at potentials more negative than active surfaces even though the driving force for peroxide reduction will be greater for the former.

Electrocatalytic or photosensitizing (photocatalytic) properties of metallophthalocyanine (MPc) complexes are dependent on the central metal. Electrocatalytic behavior is observed for electroactive central metals such as Co, Mn and Fe, whereas photosensitizing behavior is observed for diamagnetic metals such as Al, Zn and Si. In the presence of nanoparticles such as quantum dots, the photosensitizing behavior of MPc complexes is improved. Carbon nanotubes enhance the electrocatalytic behavior of MPc complexes.

Two cobalt porphyrins, (OEP)Co^II and (TPP)Co^II, where OEP and TPP are the dianions of octaethylporphyrin and tetraphenylporphyrin, respectively, were examined as electrocatalysts for the reductive dechlorination of DDT (1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane) in N,N′-dimethylformamide (DMF) containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). No reaction is observed between DDT and the porphyrin in its Co(II) oxidation state but this is not the case for the reduced Co(I) forms of the porphyrins which electrocatalyze the dechlorination of DDT, giving initially DDD (1,1-bis(4-chlorophenyl)-2,2-dichloroethane), DDE (1,1-bis(4-chlorophenyl)-2, 2-dichloroethylene) and DDMU (1,1-bis(4-chlorophenyl)-2-chloroethylene) as determined by GC-MS analysis of the reaction products. A further dechlorination product, DDOH (2,2-bis(4-chlorophenyl)ethanol), is also formed on longer timescales when using (TPP)Co as the electroreduction catalyst. The effect of porphyrin structure and reaction time on the dechlorination products was examined by GC-MS, cyclic voltammetry, controlled potential electrolysis and UV-visible spectroelectrochemistry and a mechanism for the reductive dechlorination is proposed.

In this work we report on electrochemical behavior of nickel phthalocyanine derivatives tetrasubstituted peripherally and non-peripherally with hydroxy and used to modify single walled carbon nanotubes. Nickel phthalocyanine complex octasubstituted at the peripheral positions with hydroxy groups was also used to modify single walled carbon nanotubes. Nickel phthalocyanine complex tetrasubstituted with amino groups at peripheral position was covalently and non-covalently linked to single walled carbon nanotubes. All the conjugates of nickel phthalocyanine derivatives with single walled carbon nanotubes were used for the electro oxidation of 4-chlorophenol. The nickel phthalocyanine octabsubstituted with hydroxy groups at the non-peripheral positions gave the best current response and the best resistance against electrode fouling for the oxidation of 4-chlorophenol.

We discuss here the state of the art on hybrid materials made from single (SWCNT) or multi (MWCNT) walled carbon nanotubes and MN₄ complexes such as metalloporphyrins and metallophthalocyanines. The hybrid materials have been characterized by several methods such as cyclic voltammetry (CV), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electrochemical microscropy (SECM). The materials are employed for electrocatalysis of reactions such as oxygen and hydrogen peroxide reduction, nitric oxide oxidation, oxidation of thiols and other pollutants.

Two iron porphyrins, (TPP)FeCl and (OEP)FeCl, where TPP and OEP are the dianions of tetraphenylporphyrin and octaethylporphyrin, respectively, were utilized as catalysts for the electroreductive dechlorination of α-hexachlorocyclohexane (α-HCH) which was monitored by electrochemistry, in situ UV-visible spectroelectrochemistry and controlled potential electrolysis in N,N′-dimethylformamide. GC-MS analysis of the α-HCH degradation products revealed the stepwise formation of pentachlorocyclohexene and tetrachlorocyclohexadiene as intermediates, prior to generation of the final dechlorination products which consisted of an isomeric mixture of trichlorobenzenes. Based on identification of the intermediates and final products in the reaction, an overall dechlorination mechanism of α-hexachlorocyclohexane is proposed.