Innocenzo G. Casella

Study of the electrochemical deposition and properties of cobalt oxide species in citrate alkaline solutions

Abstract Glassy carbon electrode substrates coated with thin films of cobalt oxyhydroxide were investigated in moderately alkaline medium by cyclic voltammetry. The cobalt oxide formation process was accomplished in alkaline solution (30 mM NaOH) containing millimolar concentrations of CoCl 2 and ligand species such as sodium citrate. The cobalt oxide/hydroxide films were obtained either by voltage cycling between 0.4 and 1.1 V versus SCE or under potentiostatic conditions at moderate positive potentials (i.e. 0.5 V). The resulting electrodeposited film was characterized electrochemically in alkaline solutions by cyclic voltammetry and, independently of the electrodeposition procedure adopted, reveals three well-defined sets of redox waves related to the Co(OH) 2 /Co 2 O 3 , Co 2 O 3 /CoOOH and CoOOH/CoO 2 electrochemical transitions. The charge/discharge processes and the oxygen evolution reaction during continuous potential cycling were severely inhibited in the presence of increasing concentrations of electroinactive electrolytes (i.e. NaNO 3 , K 2 SO 4 , Na 3 PO 4 , etc.). The electrochemical behaviour of the electrodeposited cobalt oxide/hydroxide film in alkaline solution and in the presence of various organic molecules was also investigated.

Electrodeposition of cobalt oxide films from carbonate solutions containing Co(II)–tartrate complexes

An electrochemical procedure of anodic deposition of cobalt oxyhydroxide film on a glassy carbon substrate in an alkaline medium (i.e. pH 11.6) is described. The electrodeposited film was obtained either by voltage cycling or by potentiostatic conditions using non-deaerated 0.1 M Na2CO3 solutions containing 40 mM tartrate ions and 4 mM CoCl2. The effects on the film formation and growth, such as tartrate–cobalt ratio, pH, applied potential, etc. were widely evaluated. The electrodeposition process, under anodic conditions and moderately alkaline solutions, most likely involves a redox transition Co(II)→Co(III)/Co(IV) with destruction of the tartrate complex and formation of insoluble oxide/hydroxide cobalt species on the glassy carbon surface. The resulting cobalt oxyhydroxide films were characterised by cyclic voltammetry (CV) in 0.1 M NaOH solutions and by scanning electron microscopy (SEM) analysis after different strategies of preparation and various electrochemical treatments. The electrochemical activity of the deposited films was checked using various organic molecules as model compounds.

Anodic electrodeposition of conducting cobalt oxyhydroxide films on a gold surface. XPS study and electrochemical behaviour in neutral and alkaline solution

A novel chemically modified electrode prepared by anodic electrodeposition of cobalt (III) film on the gold electrode substrate (Au-Co) was characterised by cyclic voltammetry and XPS techniques in both neutral and alkaline medium. Cobalt oxyhydroxide film was deposited by cycling the potential between 0.0 and 1.1 V versus SCE in 0.1 M sodium acetate solutions containing 10 mM CoCl2. The electrocatalytic properties of the Au-Co electrode were investigated in alkaline medium using glucose as a model compound. A comparative XPS study of bare gold, bare cobalt and Au-Co electrodes after electrochemical treatment in neutral and alkaline solutions has been carried out. A detailed XPS analysis of the Au4f7/2, Co2p3/2, O1s and C1s regions was performed to check the chemical composition of the Au-Co electrode upon electrochemical treatments. Film deposition is attributed to growth of conducting and compact CoOOH oxyhydroxide with significant insertion of carbonyl groups within the electrodeposited layer. The prolonged electrochemical treatment in alkaline medium produces a good stabilization of the CoIII oxyhydroxide film, with a dominant O1s feature at about 532.4 eV of BE corresponding to a non-stoichiometric surface oxygen. The absence of CoO species proves good conducting properties of the cobalt film and the absence of any passivation effects on the catalytic performance.

Amperometric determination of underivatized amino acids at a nickel-modified gold electrode by anion-exchange chromatography

A nickel-based composite electrode obtained by anodic electrodeposition of nickel (III) oxyhydroxide film on the gold electrode substrate was characterized as an amperometric sensor and successfully applied to the determination of underivatised amino acids in flow-through systems. The electrodeposition of nickel oxyhydroxide films was obtained by cycling a gold electrode between 0.0 V and +1.0 V vs. a saturated calomel electrode in a 80 microM Ni2+ solution buffered at pH 10 with NaHCO3/Na2CO3. The resulting Au-Ni composite electrode exhibits good stability in alkaline medium and can be used as an amperometric sensor of underivatised amino acids at a fixed applied potential (+0.55 V vs. Ag/AgCl). The detection limits (S/N=3) for all investigated compounds ranged between 5 and 30 pmol injected, while the linear ranges spanned over two or three orders of magnitude. The contents of several free amino acids in two sample cheeses from different brands were evaluated by calibration graphs.

Electrochemical preparation of a composite gold–cobalt electrode and its electrocatalytic activity in alkaline medium

Abstract A chemically modified electrode composed of cobalt(III) oxyhydroxide film dispersed on the gold substrate (AuCo) was characterised by cyclic voltammetry. Electrochemical deposition of the cobalt film was accomplished by cycling the potential between 0.0 V and 1.1 V (vs. saturated calomel electrode (SCE)) in 0.1 M acetate solution (at pH 7.3) containing 10 mM CoCl 2 . The effects of several experimental parameters (pH, applied potentials, etc.) on the film formation and growth were evaluated. The electrochemical behaviour of the AuCo composite electrode was investigated in alkaline medium. The film appears uniform and compact and shows good electrical conductivity and electrochemical activity towards the oxidation of several scarcely electroactive organic molecules. The concomitant presence on the electrode surface of both active catalysts leads to a wide range of potential applications where a significant electrochemical activity towards the electrooxidation of several classes of organic compounds is observed.

Determination of electroactive organic acids by anion-exchange chromatography using a copper modified electrode

An ion-chromatographic method combined with electrochemical detection at a copper-based chemically modified glassy carbon electrode (Cu-GC) has been shown to provide a simple analytical approach for the determination of some common organic acids in alkaline medium. Under the optimized isocratic chromatographic conditions (i.e. 0.1 M NaOH plus 80 mM CH3COONa), organic acids such as gallic, ascorbic, gluconic, lactobionic, galacturonic and glucuronic acid could be separated in less than 20 min. Under constant potential amperometric detection (i.e. 0.55 V vs. Ag-AgCl) the Cu-GC modified electrode allowed detection limits between 2 and 5 pmol for all investigated organic acids while the linear dynamic range spanned generally over three orders of magnitude. Examples of applications included the separation and quantitation of some common organic acids in vinegar, honey and tea samples, are given.

The Electrochemical Reduction of Nitrophenols on Silver Globular Particles Electrodeposited under Pulsed Potential Conditions

A pulsed electrodeposition technique based on a multipulse sequence of potentials of equal amplitude, duration and polarity was employed for the preparation of highly dispersed silver particles on glassy carbon surfaces (GC/Ag). A detailed analysis of the scanning electron microscope images reveals that silver deposit, obtained under pulsed electrodeposition conditions, appears as homogeneously compact and the crystallites are well dispersed on the GC substrate. The globular particles appear isolated or dispersed as twinned and rarely as trimer islands. The resulting silver modified electrode was electrochemically characterized through the reduction of nitrophenol compounds. The potential needed for the reduction of these compounds on the GC/Ag electrodes is significantly less negative than that observed on the unmodified glassy carbon electrode or bare silver substrates. Under chronoamperometric conditions, the Ag electrodeposited film shows a good catalytic activity and temporal stability regarding the electroreduction of nitrophenol compounds and can be usefully used for the electrochemical massive hydrogenation of these molecules in acidic medium. Moreover, the GC/Ag electrode was successfully tested as a sensing probe for the analytical detection of nitrophenol compounds under differential pulse voltammetric conditions showing interesting analytical performance in terms of limits of detection and dynamic linear range.

Amperometric detection of sulfur-containing compounds in alkaline media

A copper-based chemically modified glassy carbon electrode (GC-Cu) was developed to be used as an amperometric sensor for electrochemically detecting several sulfur-containing compounds in alkaline media. Under optimised flow injection conditions the calibration curves for sulfite, sulfide, thiosulfate, cysteine, cystine, etc., were linear over three orders of magnitude of concentration. Detection limits were of the order of 0.04-1.5 microM. A simple and rapid method for determining sulfite in red and white wines by anion-exchange chromatography with electrochemical detection is described.

Electrodeposition and Characterization of Nickel-Copper Alloy Films as Electrode Material in Alkaline Media

A new and simple electrochemical procedure of anodic codeposition of nickel and copper oxide-hydroxide species on the gold electrode substrate from alkaline solutions is described. The electrodeposited alloy film, with an average composition Ni:Cu of 0.67 (i.e., Ni 40 Cu 60 ) was investigated by electrochemical, scanning electron microscopy, and X-ray photoelectron spectroscopy technique. The resulting deposited alloys appear uniform, smooth, adherent to the gold substrate, and homogeneous, independently of the electrochemical procedure adopted for the preparation (i.e., potentiostatic or potentiodynamic conditions). The presence of copper oxyhydroxide species in deposited film imparts an extensive stabilization of the β/β crystallographic forms of the nickel oxyhydroxide under prolonged repetitive potential cycling in alkaline medium. The electrocatalytic activity of the resulting composite Ni-Cu film was investigated toward the oxidation of carbohydrates using glucose as a model compound.

Electrooxidation of Aliphatic Amines and Their Amperometric Detection in Flow Injection and Liquid Chromatography at a Nickel-Based Glassy Carbon Electrode

The electrocatalytic oxidation of mono- and poly-amines was investigated in alkaline solutions at a nickel-based chemically modified glassy carbon electrode. β-NiOOH exhibited electrocatalytic activity towards amines oxidation. FIA experiments were performed to test the electrode as an amperometric sensor. Under constant-potential amperometric mode (at 0.55 V vs. 4,0 M Ag/AgCl/Cl−), detection limits of all investigated analytes ranged within 1.2–3.8 pmol (S/N = 3), and the linear dynamic range extended over three orders of magnitude above the detection limits. Chromatographic separations, performed by an ion moderated partition column in alkaline solutions equipped with the Ni-CME detector, allowed very simple quantitation of aliphatic amines, avoiding tedious and time-consuming derivatization processes or postcolumn addition procedures. The Ni-CME showed good temporal stability and appreciable sensitivity.