Cobalt oxide electrodeposition on various electrode substrates from alkaline medium containing Co–gluconate complexes: a comparative voltammetric study

A study regarding the electrodeposition of Co oxides from alkaline medium containing 12?mM gluconate ligand and 12?mM Co²⁺ on glassy carbon, Au, Pt, Ni, Ti and ITO electrode substrate was carried out through cyclic voltammetry technique. Films of cobalt oxides were deposited either anodically by voltage cycling (100?mV?s^?1) between ?0.3 and 0.6?V (SCE) or by potentiostatic conditions at potential comprised between 0.2 and 0.6?V for a fixed time of deposition. Analysis of the voltammetric experimental data clearly showed that the rate of cobalt oxide electrodeposition process decreases in the order Au > Pt > GC, Ni > Ti, ITO and the massive cobalt electrodeposition does not proceed to an appreciable extent until potentials of 0.3–0.4?V (SCE) is reached. The effect of the scan rate on the peak potential, peak current, and peak-to-peak separation of the deposited cobalt oxide films was studied, and some substantial differences in terms of electrochemical behaviour in relation at the specific substrate electrode were observed and critically discussed.     

Realization of monolayer levels of surface oxidation of nickel by anodization at low temperatures

In order to examine whether monolayer or sub-monolayer extents of surface oxidation can be realized experimentally at Ni prior to onset of bulk-phase oxide formation (as they can for example at Pt, Ru or Au already at room temperature), cyclic voltammetric experiments down to low temperature (−90° C) have been conducted on Ni in solutions of NaOH in 80 mol% methanol with water. The cyclic voltammograms for the first stage of Ni oxidation to α-Ni(OH)₂, and its reduction, show that extents of surface oxidation down to an equivalent monolayer, or less, of Ni(OH)₂ can be realized at sufficiently low temperatures. However, even at these low levels of oxidation of the metal, irreversibility between the processes of Ni oxide formation and reduction is maintained in a way characteristic of the behavior of three-dimensional oxide films. It therefore appears that even at low levels of surface oxidation of Ni which are attainable at low temperature, the oxidation mechanism involves nucleation and growth of the oxide in islands rather than an initial surface-chemical process of OH or O array formation, as at Pt or Au. However, no indications of a dissolution-and precipitation type of oxide formation process, which would involve mass-transport in solution, are given by the present results obtained from experiments in dilute alkali at low temperatures, and at the rotating Ni disc electrode.     

Nickel foam-based composite electrodes for electrooxidation of methanol

Nickel foam and five nickel foam-based composite electrodes were prepared for being used as anode materials for the electrooxidation of methanol in KOH solution containing 0.1 and 1.0 M of methanol. The layered electrodes composed of nickel foam, platinum nanoparticles, polyaniline (PANI) and/or porous carbon (C) prepared in various assemblies. As shown by SEM analysis, depending on the preparation conditions, the electrodes of different morphologies were obtained. Using the cyclic voltammetry method, the oxidation of methanol on nickel foam electrode was observed in the potential range 0.4 V ↔ 0.7 V, where the Ni(OH)₂/NiOOH transformation occurred. The presence of Pt particles in electrode gave rise to the increase in electrocatalytic activity in this potential range. For electrodes containing dispersed platinum catalyst (Ni/Pt, Ni/PANI/Pt and Ni/C/Pt), the oxidation of methanol was noted also in the potential range −0.5 V ↔ 0.1 V. The electrocatalytic activities of the examined electrodes toward methanol oxidation at low potentials were in order Ni/Pt > Ni/C/Pt > Ni/PANI/Pt, whereas at high potentials in order Ni/PANI/Pt > Ni/Pt> Ni/C/Pt > Ni. Among the examined electrodes, the most resistant to cyclic poisoning appeared to be the Ni/C/Pt electrode. Presented at the 4Th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005     

Electrodeposition of platinum–nickel alloy nanocomposites on polyaniline-multiwalled carbon nanotubes for carbon monoxide redox

An electrochemical method was developed to deposit platinum (Pt)–nickel (Ni) alloy nanocomposites on polyaniline-multiwalled carbon nanotubes (Pt–Ni/PAN/MWCNTs). The material was characterized by various methods including field emission scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical techniques. An appreciably improved catalysis toward oxidation of carbon monoxide (CO) was observed at the Pt–Ni/PAN/MWCNTs nanocomposites (real ratio of Pt–Ni of 17:1), which was interpreted by a mechanism based on the bifunctional catalysis. The successful preparation of Pt–Ni/PAN/MWCNTs nanocomposites opens a new path to synthesize the promising catalysts for CO.     

Electrocatalytic reduction of dioxygen at platinum particles deposited on Nafion- and clay-coated electrodes

Nafion- and clay-coated electrodes are prepared by casting a known amount of Nafion and clay solutions on the glassy carbon electrode (GC) surface. Subsequently platinum (Pt) particles are deposited on the GC electrodes and on the Nafion- and clay-coated GC electrodes. The formation of Pt particles on the modified electrode surface is analysed by scanning electron microscope, while cyclic voltammetry provides information on the anodisation of Pt particles deposited on the GC electrodes at >0.5 V(SCE) leading to the formation of platinum oxide (PtO). The involvement of PtO on the catalysed dioxygen reduction to hydrogen peroxide is reported. Macrocyclic cobalt(III) complex is also used as the electrocatalyst. The effect of pH on the reduction of PtO and dioxygen in deaerated and oxygenated solutions is studied to understand the dioxygen reduction processes. Received: 24 January 1997 / Accepted: 14 April 1997     

Enhanced activity of gold-supported cobalt oxide for the electrochemical evolution of oxygen

Scanning electron microscopy, linear sweep voltammetry, chronoamperometry, and in situ surface-enhanced Raman spectroscopy were used to investigate the electrochemical oxygen evolution reaction (OER) occurring on cobalt oxide films deposited on Au and other metal substrates. All experiments were carried out in 0.1 M KOH. A remarkable finding is that the turnover frequency for the OER exhibited by ～0.4 ML of cobalt oxide deposited on Au is 40 times higher than that of bulk cobalt oxide. The activity of small amounts of cobalt oxide deposited on Pt, Pd, Cu, and Co decreased monotonically in the order Au > Pt > Pd > Cu > Co, paralleling the decreasing electronegativity of the substrate metal. Another notable finding is that the OER turnover frequency for ～0.4 ML of cobalt oxide deposited on Au is nearly three times higher than that for bulk Ir. Raman spectroscopy revealed that the as-deposited cobalt oxide is present as Co(3)O(4) but undergoes progressive oxidation to CoO(OH) with increasing anodic potential. The higher OER activity of cobalt oxide deposited on Au is attributed to an increase in fraction of the Co sites present as Co(IV) cations, a state of cobalt believed to be essential for OER to occur. A hypothesis for how Co(IV) cations contribute to OER is proposed and discussed.     

Electrochemical deposition and characterization of polyppyrrole coatings doped with nickel cobalt oxide for environmental applications

Electrochemical depositions of hybrid polypyrrole/nickel cobalt oxide (PPy/NiCoO) coatings onto ferritic stainless steel surface were carried out with different electrochemical techniques from 0.1 M pyrrole (Py) in 0.2-M oxalic acid (OA) solution and less than 150-nanometer-sized NiCoO particles. The structural properties of the composite were investigated by using different methods such as transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometer (EDS) and Raman spectroscopy. The embedded NiCoO particles, uniformly distributed onto the surface of the PPy film, have similar oxide ratios corresponding to a mixed oxide structure. The electrochemical characterization was done using polarization curves and linear sweep voltammetry (LSV) related to oxygen reduction reaction (ORR) in alkaline solution and hydrogen peroxide as an oxygen source. Concerning the exchange current densities for ORR, the obtained values (between 1.06 and 1.45?×?10^?3 mA cm^?2 for a total amount of NiCoO of 0.1 mg cm^?2) are comparable with other polymer films with Pt.     

Solution processed transition metal sulfides: application as counter electrodes in dye sensitized solar cells (DSCs)

A solution processed method for fabricating transition metal sulfides on fluorine doped tin oxide (FTO) as efficient counter electrodes in iodine/iodide based solar cells has been demonstrated. Conversion efficiencies of 7.01% and 6.50% were obtained for nickel and cobalt sulfides, respectively, comparable to the conventional thermally platinised FTO electrodes (7.32%). A comparable charge transfer resistance of Ni(3)S(2) and Co(8.4)S(8) to conventional Pt was found to be a key factor for such high efficiencies. Cyclic voltammetry, Kelvin probe microscopy, Electrochemical Impedance Spectroscopy, and Tafel polarization were performed to study the underlying reasons behind such efficient counter electrode performance.     

Pt–Fe cathode catalysts to improve the oxygen reduction reaction and methanol tolerance in direct methanol fuel cells

High surface area carbon-supported Pt and bimetallic Pt–Fe catalysts are investigated for the oxygen electro-reduction reaction (ORR) in low-temperature direct methanol fuel cells (60 °C). The electrocatalysts are prepared using a combination of colloidal and incipient wetness methods allowing the synthesis of carbon-supported bimetallic nanoparticles with a particle size of about 2–3 nm. These materials are studied in terms of structure, morphology and composition using X-ray diffraction, X-ray fluorescence and transmission electron microscopy techniques. The electrocatalytic behaviour of these catalysts for ORR is investigated by employing the rotating disc technique. An enhancement of the ORR is observed with the bimetallic Pt–Fe catalyst in the oxygen-saturated electrolyte solution, with and without methanol. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.     

Low loaded Pt-Co catalyst surfaces optimized by magnetron sputtering sequential deposition technique for PEM fuel cell applications: physical and electrochemical analysis on carbon paper support

A series of thin Pt-Co films with different metal ratios were deposited by using the sequential cosputtering directly on a commercial hydrophobic carbon paper substrate at room temperature and in ultra-high vacuum (UHV) conditions. Their electrocatalytic properties toward the oxygen reduction reaction were investigated in 0.5 M H₂SO₄ solution by means of cyclic voltammetry (CV) and linear sweep voltammetry (LSV) on rotating disc electrode (RDE). The results showed that Pt particles, deposited by dc-magnetron gun, surround the large Co-clusters deposited by rf-magnetron gun. In addition, the increase of Co content led to an increase in the electrochemical active surface area (EASA) from 23.75 m²/gPt to 47.54 m²/gPt for pure Pt and Pt:Co (1:3), respectively, which corresponded the improvement of the utilization of Pt by a factor of 1.91. This improvement indicated that the sequential magnetron cosputtering was one of the essential technique to deposit homogeneous metal clusters with desirable size on the gas diffusion layer by adjustment plasma parameters.     

铋膜电极方波吸附溶出伏安法测定纺织品中痕量钴和镍

本文建立了在铋膜修饰电极上采用方波吸附溶出伏安法同时测定纺织品中痕量Co2+和Ni2+的方法.以NH3-NH4Cl作为缓冲液,在丁二酮肟浓度为10 μmol/L的体系中,Co2和Ni2+的还原峰电位分别为-1.13 V和-1.03 V.当缓冲溶液pH为9.2,富集电位为-0.7V,富集时间为200 s时,C02 +和Ni2+在0.5～50 μg/L范围呈现良好的线性关系,相关系数R2＞0.99,其检出限分别为0.79 μg/L和0.96 μg/L,其它金属离子的干扰较小.采用标准加入法测定纺织品中Co>和Ni2+,回收率在94.88％～104.14％之间.     

Visualization of the Local Catalytic Activity of Electrodeposited Pt–Ag Catalysts for Oxygen Reduction by means of SECM

Pt–Ag nanoparticle co‐deposits with different Pt–Ag ratios were prepared on a glassy carbon (GC) surface by pulsed electrodeposition and investigated for their catalytic activity in electrocatalytic oxygen reduction by using cyclic voltammetry (CV), rotating disc electrode (RDE) and scanning electrochemical microscopy (SECM) in 0.1 M phosphate buffer (pH 7.0). The atomic composition of the Pt–Ag co‐deposits was studied by means of energy‐dispersive X‐ray analysis (EDAX). In combination with X‐ray diffraction (XRD), the presence of partly alloyed Pt and Ag on the GC surface was confirmed. Scanning electron microscopy (SEM) images indicate that the prepared Pt–Ag catalyst particles are homogenously dispersed over the GC surface. Their size and morphology depend on their composition. The electrocatalytic activity of Pt–Ag deposits with high Pt content was the highest, exceeding even that of electrodeposited Pt as evaluated by quantitative RDE analysis. The redox competition mode of scanning electrochemical microscopy (RC‐SECM) was successfully used to visualize the local catalytic activity of the deposited Pt–Ag particles. Semi‐quantitative assessment of the SECM results confirmed the same order of activity of the different catalysts as the RDE investigations.     

Electrocatalytic oxidation of hydrazine at cobalt hexacyanoferrate- modified glassy carbon, Pt and Au electrodes

The electrocatalytic oxidation of hydrazine has been studied on glassy carbon, Pt and Au electrodes modified by cobalt hexacyanoferrate (CoHCF) using cyclic voltammetry and rotating disc techniques. It has been shown that the oxidation of hydrazine to nitrogen occurs at the potential coinciding with that of Co(II) to Co(III) transformation in a CoHCF film, where no oxidation signal is observed at a bare glassy carbon electrode. A Tafel plot, derived from RDE voltammograms, exhibits a slope of 150 mV, indicating a one-electron charge transfer process to be the rate-limiting step. The electrocatalytic efficiency of the modified electrode towards hydrazine oxidation depends on solution pH, and the optimum range was found to be located between pH 5 and pH 7. The kinetic behaviour and location of the electrocatalytic process were examined using the W.J. Albery diagnosis table, and it was concluded that the reaction has either a “surface” or a “layer” reaction mechanism. Pt- and Au-CoHCF-modified electrodes show no significant electrocatalytic activity towards hydrazine oxidation. Received: 25 April 1997 / Accepted: 12 August 1997     

Activation of methanol-tolerant carbon-supported RuSe<Subscript>x</Subscript> electrocatalytic nanoparticles towards more efficient oxygen reduction

An electrocatalytic system that utilizes tungsten oxide modified carbon-supported RuSe_x nanoparticles is developed and characterized here using transmission electron microscopy and such electrochemical diagnostic techniques as cyclic voltammetry and rotating ring-disk voltammetry, as well as upon its introduction (as cathode) to the low-temperature hydrogen–oxygen fuel cell. After the modification of RuSe_x catalytic centers with ultra-thin films of WO₃, the potential of oxygen reduction in 0.5 mol dm⁻³ H₂SO₄ (in the absence and presence of methanol) is shifted ca. 70 mV (under rotating disk voltammetric conditions) towards more positive values, and the percent formation (at ring) of the undesirable hydrogen peroxide has decreased approximately twice when compared to the WO₃-free system. Relative to bare electrocatalyst, an increase of power density from 75 to 100 mW cm⁻² (at 300 mA cm⁻²) has been observed upon utilization of WO₃-modified RuSe_x in polymer electrolyte membrane fuel cell at 80 °C. In comparison to Vulcan-supported Pt nanoparticles, the overall electrocatalytic performance of tungsten oxide modified carbon-supported RuSe_x nanoparticles is lower, but the latter system is practically insensitive to the presence of methanol even at 0.5 mol dm⁻³ level. Dedicated to Professor Dr. Algirdas Vaskelis on the occassion of his 70th birthday.     

Pt monolayer electrocatalysts for O2 reduction: PdCo/C substrate-induced activity in alkaline media

We measured the activity of electrocatalysts, comprising Pt monolayers deposited on PdCo/C substrates with several Pd/Co atomic ratios, in the oxygen reduction reaction in alkaline solutions. The PdCo/C substrates have a core-shell structure wherein the Pd atoms are segregated at the particle’s surface. The electrochemical measurements were carried out using an ultrathin film rotating disk-ring electrode. Electrocatalytic activity for the O₂ reduction evaluated from the Tafel plots or mass activities was higher for Pt monolayers on PdCo/C compared to Pt/C for all atomic Pd/Co ratios we used. We ascribed the enhanced activity of these Pt monolayers to a lowering of the bond strength of oxygenated intermediates on Pt atoms facilitated by changes in the 5d-band reactivity of Pt. Density functional theory calculations also revealed a decline in the strength of PtOH adsorption due to electronic interaction between the Pt and Pd atoms. We demonstrated that very active O₂ reduction electrocatalysts can be devised containing only a monolayer Pt and a very small amount of Pd alloyed with Co in the substrate. Dedicated to Professor Oleg Petrii on the occasion of his 70th birthday on August 24, 2007.     

Bismuth film electrode for simultaneous adsorptive stripping analysis of trace cobalt and nickel using constant current chronopotentiometric and voltammetric protocol

Bismuth film electrode (BiFE) is presented as a promising alternative to mercury electrodes for the simultaneous determination of trace cobalt and nickel in non-deoxygenated solutions. The preplated BiFE was employed under adsorptive stripping constant current chronopotentiometric and adsorptive stripping voltammetric conditions in the presence of dimethylglyoxime complexing agent. BiFE exhibited well-defined and undistorted signals with favorable overall resolution for cobalt and nickel cations, with the signals for both metal cations being practically independent of each other. The stripping performance of BiFE is characterized by good reproducibility (RSD 1.4% for Co(II), and 4.3% for Ni(II)), low detection limits of 0.08 μg l⁻¹ for Co(II) and 0.26 μg l⁻¹ for Ni(II) employing a deposition time of 60 s, in addition to good linearity. The non-toxic character of bismuth imparts the possibility of tailoring disposable and one-shot electrochemical sensors for decentralized environmental, clinical and industrial monitoring of trace cobalt and nickel.     

Electrochemistry of the bis(1,4,7-triazacyclodecane) cobalt(III) complex and its role in the catalytic reduction of hydrogen

The electrochemistry of the bis(1,4,7-triazacyclodecane) cobalt(III) complex at a mercury electrode, HMDE, in aqueous Britton–Robinson buffer solutions was investigated using cyclic voltammetry, double-potential-step chronoamperometry and chronocoulometry. The cyclic voltammetric data were analyzed by digital simulation to confirm and to measure the heterogeneous and homogeneous parameters for the suggested electrode mechanism. Generally, the complex is electrochemically reduced giving rise to two cyclic voltammetric waves. The first wave is a diffusion-controlled reversible wave. It is assigned to the stable Co(III)/Co(II) redox couple. The second one is found to be irreversible and corresponding to a reduction of Co(II) to Co(I) species. The monovalent cobalt, highly unstable, is rapidly protonated, and then forms cobalt hydride. The hydride decomposes to hydrogen molecules and regenerates Co(II) species following a disproportionation pathway. The overall reduction mechanism is concluded to be an EECC kinetics.     

Fabrication of Trimetallic Pt−Pd−Co Porous Nanostructures on Reduced Graphene Oxide by Galvanic Replacement: Application to Electrocatalytic Oxidation of Ethylene Glycol

In present work, reduced graphene oxide nanosheets (rGO) decorated with trimetallic three‐dimensional (3D) Pt−Pd−Co porous nanostructures was fabricated on glassy carbon electrode (Pt−Pd−Co/rGO/GCE). First, GO suspension was drop‐casted on the electrode surface, then GO film reduction was carried out by cycling the potential in negative direction to form the rGO film modified GCE (rGO/GCE). Then, electrodeposition of the cobalt nanoparticles (CoNPs) as sacrificial seeds was performed onto the rGO/GCE by using cyclic voltammetry. Afterward, Pt−Pd−Co 3D porous nanostructures fabrication occurs through galvanic replacement (GR) method based on a spontaneous redox process between PtCl₂, PdCl_2, and CoNPs. The morphology and structure of the Pt−Pd−Co/rGO porous nanostructure film was characterized by scanning electron microscopy, energy dispersive spectroscopy and X‐ray diffraction method. The performance of the prepared electrode was investigated by various electrochemical methods including, cyclic voltammetry and electrochemical impedance spectroscopy. The electrocatalytic activity of the as‐prepared modified electrode with high surface areas was evaluated in anodic oxidation of ethylene glycol. The study on electrocatalytic performances revealed that, in comparison to various metal combinations in modified electrodes, trimetallic Pt−Pd−Co/rGO/GCE exhibit a lower onset potential, significantly higher peak current density, high durability and stability for the anodic oxidation of ethylene glycol. The excellent performances are attributed to the rGO as catalysts support and resulting synergistic effects of the trimetallic and appropriate characteristics of the resulted 3D porous nanostructures. Moreover, the influence of various concentrations of ethylene glycol, the potential scan rate and switching potential on the electrode reaction, in addition, long‐term stability have been studied by chronoamperometric and cyclic voltammetric methods.     

不同结构及氮掺杂NiO/rGO氧还原催化剂的制备与性能研究

本文以还原氧化石墨烯（rGO）为载体制备了片状NiO/rGO和球形NiO/N-rGO结构的氧还原催化剂. 通过X-射线衍射（XRD）、Raman（拉曼）测试、X-射线光电子能谱（XPS）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）等方法表征了两种催化剂的结构和形貌. 采用循环伏安法（CV）、Tafel曲线、线性扫描伏安法（LSV）、旋转圆盘电极（RDE）和旋转环盘电极（RRDE）等技术测试研究了两种催化剂的电化学催化氧还原性能. 研究结果表明,球形NiO/N-rGO催化剂催化氧还原的峰电流密度和起始电位（0.89 V vs. RHE）与商业化的Pt/C（20%）催化剂相近. 旋转圆盘电极（RDE）和旋转环盘电极（RRDE）测试证明,在碱性电解液中NiO/rGO和NiO/N-rGO催化的氧还原反应均主要通过4?鄄电子途径反应途径发生,球形NiO/N-rGO催化剂展现出替代Pt/C基催化剂的潜力.     

Simultaneous Determination of Nickel and Cobalt Using a Solid Bismuth Vibrating Electrode by Adsorptive Cathodic Stripping Voltammetry

A simple, fast, sensitive and greener voltammetric procedure for simultaneous analysis of nickel (Ni) and cobalt (Co) by square wave adsorptive cathodic stripping voltammetry (SW‐AdCSV) using a solid bismuth vibrating electrode is presented for the first time. The procedure enables to determine Ni together with Co, in ammonia buffer 0.1 M (pH 9.2) and in the presence of oxygen, and involves an adsorptive accumulation of metal‐dimethylglyoxime (Ni‐DMG and Co‐DMG) complexes on the electrode surface. For Ni and Co, the detection limits, obtained with 30 s of accumulation time, were 0.6 and 1.0 µg L^?1, respectively. The method was free of metals (Cd²⁺, Cr³⁺, Cr⁶⁺, Cu²⁺, Fe³⁺ and Pb²⁺ up to 50 µg L^?1, Al³⁺ and Mn²⁺ up to 500 µg L^?1; Zn²⁺ up to 300 µg L^?1) interferences up to the concentrations mentioned in brackets. The proposed method was validated for simultaneous determination of Ni and Co in a certified reference surface and river waters with good results.