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CoN4 complexes like Co phthalocyanines (CoPc) have been extensively studied as electrocatalysts for the oxygen reduction reaction (ORR) but they only promote the 2-electron reduction of O to give peroxide. In contrast, vitamin B a Co macrocyclic naturally occurring molecule has attracted the attention of the scientific community because instead of catalysing the 2-electron reduction of O to HO like the other Co macrocycles it promotes the 4-electron reduction to HO. Vitamin B possesses an axial back ligand and this seems to be the reason for its higher activity and selectivity for the 4-electron reduction of O. To test this hypothesis, we synthetized a CoPc axially coordinated to pyridine anchored to carbon nano-tubes (CoPc-Py-CNT). The Co centre is therefore coordinated to 5 N as in vitamin B. The modified CoPc containing catalytic material was characterized by EPR and XPS spectroscopy. Ab initio calculations, Koutecky– Levich extrapolation and Tafel plots well describe the similarities between the 2 complexes and reveal insights into the mechanism of action of Co penta-coordinated complexes. According to our results the pyridine back ligand increases the Co-O binding energy and making it more similar to that of Vitamin B, favouring the splitting of the O-O bond. The back ligand then plays a crucial role in modifying Co-O binding energy which is a well know reactivity descriptor.

International audience; This is an overview of the electrochemical characterization of nickel and stainless steel as electrodes in medical devices for the early diagnosis of small fiber neuropathy that originates from type-2 diabetes or cystic fibrosis. The electrical current responses obtained during the clinical tests are related to the amount of chloride present on the sweat. Stainless steel electrodes are now used to replace nickel because this later not only presents problems with chloride sensitivity but its contact with skin can cause possible allergic reactions for some patients. For the above reasons, several types of stainless steels were studied. It was shown that some of them perform well and have lower costs than Ni electrodes. We discuss the state of the art of the electrochemical studies conducted with nickel and steels under physiological or biomimetic conditions and discuss the advantages of a particular steel over the others depending on the conditions, especially chloride concentration.

Herein, we present a novel method to design nanoscale molecular wires by exploiting well-established electrocatalytic molecular platforms based on metallophthalocyanine blocks. Metallophthalocyanines exhibit high catalytic activity for a wide variety of electrochemical reactions of practical interests. To this aim, metallophthalocyanine molecules can be attached to an electrode surface via a conjugated mercaptopyridine axial ligand that provides (i) stable chemical binding to the metal surface through the thiol-anchoring group, and (ii) a good electrical communication between the metallophthalocyanine ring and the electrode surface. Our previous work demonstrates that long mercaptopyridinium blocks act as excellent linkers in such electrocatalytic platform, resulting in an optimal electrocatalytic activity of the metallophthalocyanine unit. Here we profit from this optimized electrocatalytic molecular platform to design new molecular wires that connect a metal nanoscale junction in a highly efficient and tunable way. To this aim, we use an STM break-junction approach to control the formation of a nanometric gap between two Au electrodes, both functionalized with mercaptopyridinium (bottom) and mercaptopyridine (top). When metallophthalocyanine is introduced into the functionalized metal nanojunction, stable molecular connections between the two electrodes are formed through axial coordination to the top and bottom pyridine moieties. We show that the highest conductance of the resulting nanoscale molecular wire corresponds to an Fe-phthalocyanine as compare to a Cu-phthalocyanine, which follows the electrocatalytic trend for such molecular systems. These results not only demonstrate a new strategy to design new families of highly conductive and tunable nanoscale molecular wires, but it also brings a new nanoscale electrical platform to help understanding some fundamental mechanistic aspects of molecular electrocatalysis.

We report here a novel approach to the template-assisted electrochemical synthesis of vertically aligned polyaniline (PANI) nanostructure surface arrays. When PANI is obtained by electropolymerization inside a custom-made anodic aluminum oxide (AAO) template, with an Au layer sputtered onto one side of the AAO acting as an anode, PANI nanotubes are obtained. In contrast, when the surface of this gold layer is modified with 4-aminothiophenol (4-ATP) as a self-assembled monolayer (SAM) film anchored to the gold layer via the thiol groups and on the opposite end having NH2 functionalities, we obtain a surface array of PANI nanowires. Cyclic voltammetry and SEM analysis show that the amino functionalities of Au/SAMs act as a nucleation site in the internal base of the AAO pore and determine both the morphology and structure of polyaniline and its electronic properties as well.

Cyrhetrenyl crown ether complexes [(η5-C5H4CH N-M)Re(CO)3] (where M = 4-benzo-15-crown-5 (3a), 4-benzo-18-crown-6 (3b), 2-methyl-15-crown-5 (3c), or 2-methyl-18-crown-6 (3d)) were synthesised from cyrhetrenylcarboxaldehyde (1) and the corresponding crown ether amines 2a–d. All the complexes were characterised by IR spectroscopy, 1H and 13C NMR spectroscopies, and mass spectrometry. The stereochemistry for imine compounds 3a–d were determined using the 1H and 13C NMR spectroscopy data, which indicated that these complexes have the anti-(E) conformation. This was also confirmed by the X-ray crystal structures of 3b and 3c in the solid state. Additionally, the electrochemical behaviours of 1 and 3a–d were studied.

The recently introduced new electroanalytical protocol of stripping voltammetry microprobe (SPV) has been considerably improved with respect to analytical performance. The determination of the silver ions is shown to be possible by the precipitation of a solution of silver drops on an electrode surface, which is previously moistened with a solution of NaCl. The electrode thus modified, i.e., with the silver chloride precipitate on the surface, is introduced into a chloride electrolyte and is negatively polarized to reduce the silver salt to metallic silver. Whereas this reduction process produces only a broad signal, the following electrochemical oxidation of the silver metal back to AgCl provides a highly sensitive and narrow signal, which lends itself for analysis. The linear range for determination of silver ions following this protocol is 1.4 × 10 −7 to 7.4 × 10 −4 mol L −1 and the detection limit is 4.6 × 10 −8 mol L −1 .

We have compared the electrocatalytic activity of several substituted and unsubstituted Co and Fe N4-macrocyclic complexes (MN4) for the electro-reduction of oxygen with the complexes directly adsorbed on the edge plane of pyrolytic graphite or adsorbed on carbon nanotubes (CNTs). In the presence of CNTs, one order of magnitude higher surface concentrations of MN4 catalysts per geometric area unit could be adsorbed leading to a lower overpotential for the oxygen electro-reduction and activities in the same order of magnitude as the commercially available Pt/C catalysts in basic pH. From Koutecky-Levich regression analysis, the total number of electrons transferred was approximately 2 for all the Co complexes and 4 for all the Fe ones, both in the presence and in the absence of the carbon nanotubes. Furthermore, the Tafel slopes did not vary due to the presence of the CNTs and presented values in the range of -0.06 V decade

An efficient and inexpensive catalyst for the oxygen reduction reaction (ORR) is the key missing component for large-scale development of fuel cells. Bio-inspired tethered electrocatalysts could be the solution to this problematic reaction. Either unsubstituted Fe phthalocyanine (FePc) or Fe hexadecachloro-phthalocyanine (16(Cl)FePc) was anchored to carbon nanotubes (CNTs) via a pyridine axial ligand. The results show that the fifth coordination plays a major role in increasing the catalytic activity of FePc and 16(Cl)FePc for the ORR. The coordination also allows the decoupling of the metal centre from the carbon support, thus changing the geometrical and electronic structure and hindering the production of HO. The pentacoordinated catalysts were stable in acidic pH according to the rotating disk analysis, but the activity of the hexadecachloro compound was not higher than that of the unsubstituted phthalocyanine. Cl atoms reduced the coupling between O and Fe, mismatching the energy of the frontier orbitals and lowering the activity towards the reduction of O.

We have prepared a nanoelectrode ensemble containing vertically aligned single walled carbon nanotubes (SWCNTs) using a non-template molecular self-assembling strategy. We used a bottom-up construction approach to assemble amino functionalized SWCNTs ( af- SWCNTs) in a well-defined architecture. These af- SWCNTs were linked and vertically aligned to pre-formed self-assembled monolayers of 4-MBA. A Cobalt(II) tetracarboxyphthalocyanine (Co(COOH) 4 Pc) complex was covalently bonded to external portion of af- SWCNTs to complete the final nanoelectrode ensemble. X-ray photoelectron spectroscopy (XPS) and Atomic Force Microcopy (AFM) confirmed the effectiveness of the assembling steps on the gold surface starting from the Au/MBA SAMs. The system Au/4-MBA/ af- SWCNTs shows an interface with large ordered array, which exhibits a high activity for the electrooxidation of L-cysteine (L-cys). Theoretical calculations suggest that the incorporation of the af -SWCNTs increased the activity of the assembly to electronic transfer and it was observed that the electrooxidation reaction is energetically favorable.

In this work, we have studied the interaction between the hydrazine N 2 H 4 molecule with several FeN4 macrocyclic complexes (FePc's). In order to modulate the electron density located on the metal center using iron-phthalocyanine (FePc) as the reference, we used substituted iron-phthalocyanines with different types of substituents electron-donating groups such as iron-tetraamino-phthalocyanine (4β(NH 2 )FePc) and iron-octamethoxyphthalocyanine (8β(OCH 3 )FePc), and with electron-withdrawing groups such as iron-tetranitrophthalocyanine(4β(NO 2 )FePc) and iron-hexadecachlorophthalocyanine (16(Cl)FePc), respectively. We have found that the energy of interaction between hydrazine and the Fe center in the macrocycle increases as the electron-withdrawing power of the substituents increases. When rate constants instead of currents are compared in a semilog plot versus Δ ɛ D-A , a linear correlation is found where log k increases as the intermolecular hardness of the systems decreases.

This paper describes how electrochemical trace analysis can be performed in micro samples based on the precipitation of a sparingly soluble compound and its immobilization on an electrode surface. Precipitation is performed in a solution droplet put on the electrode in an upside-down position in air. The solvent of the droplet is then evaporated and the immobilized residue is subjected to a voltammetric measurement after introducing the electrode to an electrolyte solution. This methodology can be used for the quantification of dissolved ions (after precipitation) as well as for that of dispersed solids. As example, here the quantification of silver ions following precipitation as AgCl is described. Keywords: Stripping voltammetry, Precipitation, Immobilization, Electrochemistry, Microanalysis

The construction of self-assembled iron phthalocyanine (FePc) systems on gold electrodes modified by self-assembled monolayers (SAMs) is becoming an interesting strategy for obtaining electrocatalytic molecular building blocks for the oxygen reduction reaction (ORR). In this work, we have measured the conductance of pyridiniums axial ligands at the single molecule level using the scanning tunneling microscope-based break-junction method (STM-Break Junction) to study the role of the axial ligand on the activity of the self-assembled FePc systems on a gold electrode surface. The electron-pulling effect of pyridinium axial ligands is known to increase the electrocatalytic activity of FePc for the oxygen reduction reaction (ORR). We have used these systems as a platform for carrying out a comparative study for understanding the real influence of the proximal axial ligands. Further, these ligands act as molecular wires between the gold electrode surface and the FePc molecule. The pyridinium molecules were synthesized following a series of structural variations using a basic molecular backbone. From conductance measurements obtained for each pyridinium molecule, it was possible to establish that electron transport through each pyridinium does not influence the activity of FePc for ORR in alkaline media. In addition, the DFT calculations shows that the axial ligand in FePc modifies its catalytic activity by decreasing the binding energy of O2 to the Fe site.

Schiff derivatives were prepared by the reactions of salicylaldehyde and its derivatives (5-chloro, 5-methoxy, 5-fl uoro, 5-methyl, 5-nitro) with the amino group of chitosan. The Schiff bases were studied by Fourier IR spectroscopy and by UV-visible spectroscopy. The cyclic voltammograms of the Schiff bases were analyzed and compared to those of chitosan and salicylaldehyde. The formal potential of the chitosan Schiff base derivative correlates with the Hammett parameters. The oxidation potential increases and the optical density decreases with enhancement of the electron-acceptor properties of the functional group R in the m-position to the -N=CH- group. Chitosan (Chi) is a polysaccharide whose chains consist of recurrent units of acetamido-2-deoxy-D-glucode linked by the 1,4-β-glycoside bond. This polysaccharide was widely studied as drug carrier (1, 2), because it is nontoxic, biodegradable, and well biocompatible (3).

In classical volcano correlations in electrocatalysis, the shape of (log io) plots versus the binding energy of the reactant to active sites, the maximum activity is associated to a situation where the surface coverage of reactant species is equal to 0.5 corresponding to a free energy of adsorption of the reactant equal to zero. When studying electrochemical reactions catalysed by macrocyclic transition metal complexes adsorbed on graphite electrodes, volcano correlations are found when plotting the activity versus the formal potential of the catalyst for several reactions, assuming that the formal potential is somehow related to the free energy of the adsorption of the reacting molecule. In this work we offer an interpretation different from that given in the literature for these correlations for the electrooxidation of hydrazine. The highest catalytic activity is achieved when the formal potential of the catalyst approaches the N2H4/N2 reversible potential. In contrast, if log i (normalized for the actual surface concentrations of Fe(II) active sites at constant potential) is plotted versus the difference between the Fe(II)/(I) formal potential of the catalysts and the standard potential of the N2H4/N2 reaction, the correlation is linear with a slope close to 2RT/F. Keywords: Falling region, Tuning formal potential, Design best catalyst, Surface redox catalysis

The need of deeper insights regarding the inner working of catalysts represents a current challenge in the search of new ways to tune their activities towards new chemical transformations. Within this field, metallophthalocyanines-based (MPc) electrocatalysis has gained tremendous attention due to their versatility, low cost, great stability and excellent turn-over properties. In this concern, here we present a quantum chemical study of the formation of supramolecular complexes based on the adsorption of MPcs on gold substrates, and the effect of the substrate on their electrocatalytic properties. For this purpose, we used iron- (FePc), cobalt- (CoPc) and copper-phthalocyanines (CuPc). To model the gold surface we used two gold clusters of different sizes, given by Au26 and Au58 accounting for gold electrode Au(111) surface. Thus, both electronic and binding strength features of the adsorption process between the complexes were analyzed in detail in order to gain a deeper description of the nature of the MPc–Au(111) formation, by using Density Functional Theory (DFT) calculations, at the PBE and TPSS levels including the dispersive contribution according to the Grimme approach (D3). Our results show that dispersion forces rule the MPc–gold interaction, with binding strengths ranging between 61 and 153 kcal mol−1, in agreement to the reported experimental data. To provide a detailed picture of our findings we used the non-covalent interactions index (NCIs) analysis, which offers additional chemical insights regarding the forces that control their interaction strength. Finally, our calculations revealed that among the three MPcs, CuPc required less energy for its oxidation. However, the removal of the electron involves a tremendous decrease of the MPc–gold surface interaction strength thus suggesting its desorption, which would prevent the required reversibility of the redox reaction, explaining its low performance observed experimentally.

Similarities are established between well-known reactivity descriptors of metal electrodes for their activity in the oxygen reduction reaction (ORR) and the reactivity of molecular catalysts, in particular macrocyclic MN4 metal complexes confined to electrode surfaces. We show that there is a correlation between the MIII /MII redox potential of MN4 chelates and the M-O2 binding energies. Specifically, the binding energy of O2 (and other O species) follows the MIII -OH/MII redox transition for MnN4 and FeN4 chelates. The ORR volcano plot for MN4 catalysts is similar to that for metal catalysts: catalysts on the weak binding side (mostly CoN4 chelates) yield mainly H2 O2 as the product, with an ORR onset potential independent of the pH value on the NHE scale (and therefore pH-dependent on the RHE scale); catalysts on the stronger binding side yield H2 O as the product with the expected pH-dependence on the NHE scale. The suggested descriptors also apply to heat-treated pyrolyzed MN4 catalysts.

Tetrapyrrolic macrocycles, such as porphyrin, consisted of four pyrrole units bonded by different bridges, for example methene in the case of porphyrins and azamethene in the case of phthalocyanines. They can complex metal ion transition and the synthesized metallocomplexes are extremely stable. The (electro) chemical properties of MN4 complexes have been widely studied and have been particularly used for the catalysis of electrochemical reactions in homogeneous solutions. The development of electrodes with attached MN4 complexes is also particularly attractive for electrocatalysis of reactions of interest, with an easy separation of catalysis products from the catalyst. This chapter describes the development and use of modified electrodes with a focus on metalloporphyrin and metallophthalocyanine complexes (MPcs) for electrocatalysis and electroanalysis of thiol oxidation. First, the main preparation and characterization ways of MN4-modified electrode are presented, as well as the development of recent immobilization strategies. The latest development of hybrid electrode materials combining MN4 macrocycles and nanoobjects are also described, with emphasis on their electrochemical properties. Finally, the main examples of development MN4-modified electrodes for the electroanalysis of thiols are commented.

et al., We studied the electronic and conductance properties of two thiophene–curcuminoid molecules, 2-thphCCM (1) and 3-thphCCM (2), in which the only structural difference is the position of the sulfur atoms in the thiophene terminal groups. We used electrochemical techniques as well as UV/Vis absorption studies to obtain the values of the HOMO–LUMO band gap energies, showing that molecule 1 has lower values than 2. Theoretical calculations show the same trend. Self-assembled monolayers (SAMs) of these molecules were studied by using electrochemistry, showing that the interaction with gold reduces drastically the HOMO–LUMO gap in both molecules to almost the same value. Single-molecule conductance measurements show that molecule 2 has two different conductance values, whereas molecule 1 exhibits only one. Based on theoretical calculations, we conclude that the lowest conductance value, similar in both molecules, corresponds to a van der Waals interaction between the thiophene ring and the electrodes. The one order of magnitude higher conductance value for molecule 2 corresponds to a coordinate (dative covalent) interaction between the sulfur atoms and the gold electrodes., This work has been funded by the FONDECYT REGULAR grants 1110206,1140770, and 1140199, PAI-CONICYT 79150041, Conicyt PFCHA 21140734, ANILLO project Act 1117, Millenium Project RC120001, the Dutch funding agencies FOM and NWO/OCW, by the EU through a RISE (DAFNEOX) project, SEP-210165479 by the MICINN of Spain (projects CTQ2012-32247 and MAT2013-47869- C4-2-P). N.A.-A. and R.D.-T. also acknowledge financial support from MINECO through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496).

The antimicrobial effect of incorporating silver nanoparticles (AgNps) into zirconia matrix–polyether glycol was studied. AgNps of 4–6 nm in size were synthesized using the inverse micelles method, and different doses of metallic nanoparticles were incorporated into zirconia–polyether glycol mixtures during the ageing procedure. Atomic force microscopy (AFM) of the modified hybrid film showed a homogenous distribution of 20–80 nm diameter AgNps, indicating agglomeration of these structures during film modification; such agglomerations were greater when increasing the dosage of the colloidal system. The AgNps-hybrid films showed higher antimicrobial activity against Gram-positive bacteria than for Gram-negative bacteria. Hybrid films prepared with dioctyl sodium sulfosuccinate (AOT) stabilized AgNps presented enhanced antibacterial activity compared to that obtained through the addition of a high AgNO3 concentration (0.3 wt%).

We discuss here the state of the art on hybrid materials made from single (SWCNT) or multi (MWCNT) walled carbon nanotubes and MN4complexes 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.

In this review, we describe and discuss the developments in the use of metalloporphyrins and metallophthalocyanines as catalysts for oxygen reduction in aqueous electrolytes. The main goal of most researchers in this field has been to design catalysts which can achieve facile reduction of oxygen by the four-electron transfer pathway at the lowest overpotential possible. With this in mind, the primary objective of this review was to bring to light the research frontiers uncovering important milestones towards the synthesis and design of promising N4-metallomacrocyclic catalysts which accomplish the four-electron reduction of oxygen, and, based on literature, to draw attention to the fundamental requirements for synthesis of improved catalysts operating at low overpotentials. Our emphasis was not to make parallel comparisons between individual classes of N4-metallomacrocyclic complexes with respect to their activity, but rather to focus on the commonalities of the fundamental properties that govern their reactivities and how these may be aptly manipulated to develop better catalysts. Therefore, besides discussion of the progress attained with regard to synthesis and design of catalysts with high selectivity towards four-electron reduction of O2, a major part of the review highlights quantitative structure-activity relationships (QSAR) which govern the activity and stability of these complexes, which when well understood, refined and carefully implemented should constitute a fundamental gateway for rational design of better catalysts.

We have studied the electrochemical kinetics of anodic Ni dissolution as a function of chloride ion concentration, at pH 5, 6 and 7, in order to mimic the conditions of sweat samples. Our results show that the rate-determining step for Ni dissolution in the mentioned pH range is the transfer of one first electron, as suggested by the Tafel slopes close to 0.120 V/decade. However, the reaction order in chloride ion varies from ca. 2 at pH 7 to values close to unity for pH values between 5 and 6. This finding is very important for sensor applications in sweat fluids since the sensitivity of the Ni electrode to chloride ions is higher in neutral solutions (pH ca. 7) compared to that in slightly acid solutions (pH between 5 and 6). Small variations in pH in real samples are expected so this change in sensitivity should be considered when sensing chloride ions in sweat fluids.

A new hybrid sol–gel type film, composed of tetraethylorthosilicate (TEOS) and tetraocthylorthosilicate (TEOCS), and modified with different nanoparticle systems, has been investigated as a coating for protection of AA-2024-T3 aluminium alloy. The nanoparticle systems considered were either ZrO2 or CeO2 or their combination. The zirconia nanoparticles were prepared from a Zr (IV) propoxide sol (TPOZ), using an organic stabilizer, and the CeO2 nanoparticles were developed spontaneously after adding cerium nitrate solution to the hybrid sol. The chemical composition and the structure of the hybrid sol–gel films were examined by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion resistance of the coated AA-2024 alloy was examined by potentiodynamic polarization. The results revealed that, for short exposure times in the electrolyte, incorporation of ZrO2 or CeO2 nanoparticles in the hybrid film does not provide an increase in the corrosion resistance of the coated AA-2024 alloy. Further, the resistance was significantly reduced by increasing the nanoparticle content. Conversely, by incorporating both nanoparticles (ZrO2 and CeO2), the corrosion resistance of the resulting hybrid films increased slightly. The behavior changed significantly when the coated alloy was exposed to the electrolyte for 5 days. The corrosion resistance of the coatings, unmodified and modified with CeO2 or ZrO2 nanoparticles, decreased by two or three orders of magnitude, while the film modified with both nanoparticles (CrO2 and ZrO2) showed a relatively high corrosion resistance and responsiveness to activation processes during anodic polarization.

This article is a historical overview of free energy relationships in electrochemistry with the purpose of giving the reader an integrated view on how these correlations are interconnected in various aspects starting with free energy correlations for outer-sphere and inner-sphere processes, Tafel correlations, the Butler–Volmer equation, and electron transfer theories. The citation of the literature is far from complete and is aimed to stimulate the reader to further reading.

We have revisited correlations between catalytic activity and formal potentials of MN4 catalysts for the reduction of O2 (ORR). When comparing the activities of Cr, Mn, Co and Fe MN4 complexes for ORR as a plot of (log i/n)E versus the M(III)/(II) formal potential of the catalyst (n = number of electrons involved in the ORR), two linear correlations are obtained: one for Cr, Mn and Fe complexes and another for Co complexes. Mn and Fe are 4-electron reduction catalysts and Cr and Co are 2-electron reduction catalysts for ORR in alkaline media. We show that instead of plotting the formal potential E°′ of the catalyst but the difference between this parameter and the reversible potential Erev of the corresponding catalytic reaction (O2/OH−) or (O2/HO2−), as (E°′ − Erev) and using the Co(II)/(I) formal potential for cobalt macrocyclics, instead of the Co(III)/(II) redox couple, all data points merge into one single linear correlation of slope +0.170 V/decade. It is possible that when (E°′ − Erev) approaches zero, the maximum activity could be achieved and this is especially important for 4-electron catalysts and the linear correlation might be part of an incomplete volcano correlation. Keywords: Linear correlations, Phthalocyanines, Fe porphine, O2 reduction catalyst, Redox potentials

Metallophthalocyanines confined on the surface of electrodes are active catalysts for a large variety of electrochemical reactions and electrode surfaces modified by these complexes can be obtained by simple adsorption on graphite and carbon. However, more stable electrodes can be achieved by coating their surfaces with electropolymerized layers of the complexes, that show similar activity than their monomer counterparts. In all cases, fundamental studies carried out with adsorbed layers of these complexes have shown that the redox potential is a very good reactivity index for predicting the catalytic activity of the complexes. Volcano-shaped correlations have been found between the electrocatalytic activity (as log I at constant E) versus the Co(II)/(I) formal potential (E°′) of Co-macrocyclics for the oxidation of several thiols, hydrazine and glucose. For the electroreduction of O2 only linear correlations between the electrocatalytic activity versus the M(III)/M(II) formal potential have been found using Cr, Mn, Fe and Co phthalocyanines but it is likely that these correlations are “incomplete volcano” correlations. The volcano correlations strongly suggest that E°′, the formal potential of the complex needs to be in a rather narrow potential window for achieving maximum activity, probably corresponding to surface coverages of an M-molecule adduct equal to 0.5 and to standard free energies of adsorption of the reacting molecule on the complex active site equal to zero. These results indicate that the catalytic activity of metallophthalocyanines for the oxidation of several molecules can be “tuned” by manipulating the E°′ formal potential, using proper groups on the macrocyclic ligand. This review emphasizes once more that metallophthalocyanines are extremely versatile materials with many applications in electrocatalysis, electroanalysis, just to mention a few, and they provide very good models for testing their catalytic activity for several reactions. Even though the earlier applications of these complexes were focused on providing active materials for electroreduction of O2, for making active cathodes for fuel cells, the main trend in the literature nowadays is to use these complexes for making active electrodes for electrochemical sensors.

Catalysts for the oxygen reduction reaction (ORR) were prepared on carbon black (C) using FeIIphthalocyanine (FePc) and Cl–FeIIItetramethoxyphenylporphyrin (ClFeTMPP), as Fe precursors with and without a pyrolysis step at 800 °C. CO poisoning of the ORR catalytic sites for all these Fe/N/C electrocatalysts was attempted at pH 1 and 13, but to no avail, even if an iron ion is known to occupy the center of the active sites in at least the unpyrolyzed FePc/C or ClFeTMPP/C. The exact nature of the active center of these Fe-based heat-treated catalysts may still be a subject of debate but, in light of the absence of CO poisoning for unpyrolyzed FePc/C and ClFeTMPP/C, resistance to CO poisoning by the heat-treated catalysts cannot be used as evidence that the active center of their catalytic site is devoid of iron. Keywords: Fuel cell, Non-noble metal catalyst, CO, Oxygen reduction

Bis(N-alkyl-2-oxy-1-naphthaldiminato)copper(II) complexes in the solid state and in N,N'-dimethylformamide (DMF) solutions were studied by electronic spectroscopy, X-ray diffraction, DFT calculations, and cyclic voltammetry. The established correlation between the bulkiness of the imine nitrogen substituent, deformation of the copper coordination sphere, and the Cu II /Cu I couple potential in DMF solutions has been re-evaluated, and its inconsistencies explained by using results from DFT calculations and spectroscopic data. According to these DFT calculations, the coordination sphere of the N-ethyl derivative has a flat-tetrahedral geometry. The N-Cu-N' and O-Cu-O' angles and the dihedral angle between the planes N-Cu-O and N'-Cu-O' in the solid state found by X-ray diffraction in this study are affected by crystal packing forces. UV/Vis spectra of the N-ethyl, N-iPr, and N-tBu derivatives suggest that the first two compounds have fluxional behavior characterized by a centrosymmetric transition state, whereas the tBu group in the N-tBu derivative prevents such dynamic action. In the crystal, this N-tBu complex changes upon DFT geometry optimization to a more tetrahedral configuration. Therefore, in contrast to X-ray crystal structures reported in the literature of complexes with primary N-alkyl substituents that show a planar Cu coordination sphere (i.e. N-Cu-N' and O-Cu-O' bond angles of 180°), these complexes are not planar in solution or as isolated molecules.

We have investigated the electrocatalytic activity of tetraphenyl porphyrin, of substituted tetraphenyl porphyrins and of vitamin B 12 for the electro-oxidation of 2-aminoethanethiol, with the catalysts confined on graphite electrodes. Several N4-macrocyclic were used in order to have a great variety of formal potentials of the catalysts and compare this parameter with the catalytic activity. The electrocatalytic activity, measured as current at constant potential, increases with the formal potential of the catalysts as follows: Co-pentafluorotetraphenylporphyrin 12 . Vitamin B 12 exhibits the maximum activity. A correlation of log I (at constant potential) vs. the formal potential E ′ of the catalysts gives a volcano correlation when data of Co-phthalocyanines studied in previous work is included in the comparison. This clearly shows that the search for better catalysts for this reaction point to those N 4 -macrocyclic complexes with Co(II)/(I) formal potentials close to −1.0 V vs. SCE which corresponds to an optimum situation for the interaction of the thiol with the active site. When comparing reactivity trends of similar catalysts for the oxidation of other thiols ( l -cysteine, mercaptoacetate and 2-mercaptoethanol) E ′ max correlates linearly with the p K a of the thiol.

The electrocatalytic activity of a series of Co macrocyclic complexes confined on graphite electrodes for the oxidation of thiols : 2mercaptoethanol, 2-mercaptoacetate, 2-aminoethanethiol and l-cysteine give volcano correlations between catalytic activity of the metallo complexes and the formal potential of the complex. The formal potential that gives the maximum activity correlates linearly with the pKa of the thiol. We have extended previous studies for the oxidation of hydrazine using Co and Fe macrocyclics and obtain volcano correlations for this reaction as well. The slope of the rising region of the volcano (where the catalytic activity increases with the driving force of the catalyst) gives values of ca. +0.120 V/decade which is the theoretical value when using a Langmuir isotherm for the adsorbed thiol or hydrazine molecule on the reacting site. These results indicate that is possible to "tune" the redox potential of the complexes to attain maximum activity.

In this paper the preparation and characterization of modified electrodes based on carbon nanotubes / pyrrole / cobalt phthalocyanine was done to obtain hybrid materials for the electrochemical oxidation of 2-mercaptoethanol. To prepare these new electrodes, two steps were followed. First, single-walled CNT (SWNT) deposits were made in aqueous solution on glassy carbon (GC) to obtain GC/CNT electrodes. Subsequently, pyrrole (Py) was incorporated on the CNTs to produce GC/CNT/PPy electrodes by electropolymerization. Pyrrole electropolymerization was a useful method to control the film characteristics. Both deposits were studied using a redox model reaction with ferrocenemethanol (FeMeOH), enabling the determination of the stability and charge transfer characteristics of the obtained electrodes. Finally, CoPc was incorporated into the hybrid electrodes, and their response for the oxidation of 2-mercaptoethanol was investigated.

The electrocatalytic reduction of SO2 in aqueous media was studied as a function of the pH at a glassy carbon electrode modified with poly[Cu(II)-5,7,12,14-tetramethyldinaphtho[b,i]-1,4,8,11-tetraaza[14]annulene] film. The best amperometric response was obtained at pH = 1 and the activity decreased upon pH increasing. The SO2 reduction potential in this condition was shifted ca. 220 mV in the anodic direction compared to the value observed in bare glassy carbon. The Tafel slope, 278.64 mV dec−1, and the charge transfer coefficient, 0.18, are consistent with some interaction between SO2 and the modified electrode. The amperometric response is linear up to a 0.1 mM SO2 concentration, the detection limit being 0.02 mM under optimized conditions.

The effect of zirconia and zirconia-polyester glycol hybrid coatings on the corrosion resistance of mechanically polished or anodized AISI 316 stainless steel (316L), was studied by potentiodynamic polarization and electrochemical impedance spectroscopy in 0.1 M NaCl and scanning electron microscope and atomic force microscopy examinations. The deposition of zirconia coatings was achieved by the sol–gel technique by immersing the samples in either the inorganic polymer or the organic–inorganic polymer mixture. From potentiodynamic and impedance measurements, the grade of protection is reduced with the exposure time to the electrolyte, which is mainly associated with lost of film adhesion and, consequently, detachment from the metal substrate. However, the uncoated anodized sample revealed an unexpected corrosion behavior; the anodic film formed during anodizing readily increased the corrosion resistance of the 316L stainless steel in 0.1 M NaCl, revealing a considerable reduction in the corrosion current density and an increase in the pitting potential.

We report here a fast procedure to modify glassy carbon (GC) electrode using commercially available unsubstituted cobalt phthalocyanine (CoPc) and tetrasulfonated substituted nickel phthalocyanine (NiTSPc) simply adsorbed on oxidized single walled carbon nanotubes SWCNT. The electrocatalytic activity of the resulting SWCNT-MPc nanocomposite materials was evaluated toward the oxidation of two biologically relevant molecules, namely 2-mercaptoethanol (2-ME) and nitric oxide (NO). The obtained electrodes are highly stable under hydrodynamic conditions and the tailored hybrid surfaces allow enhancing electron transfer for the electrocatalytic oxidation of 2-ME and NO. Keywords: Single walled carbon nanotube, Cobalt phthalocyanine, Nickel tetrasulfonated phthalocyanine, Electrocatalysis, 2-Mercaptoethanol, Nitric oxide

We have investigated the electrocatalytic activity of several substituted and unsubstituted cobalt–phthalocyanines of substituted tetraphenyl porphyrins and of vitamin B12, for the electro-oxidation of 2-mercaptoacetate, with the complexes pre-adsorbed on a pyrolytic graphite electrode. Several N4-macrocyclic were used to have a wide variety of Co(II)/(I) formal potentials. The electrocatalytic activity, measured as current at constant potential, increases with the Co(II)/(I) redox potential for porphyrins as Co–pentafluorotetraphenylporphyrin Co–octamethoxyphthalocyanine > Co–tetranitrophthalocyanine Co–tetraaminophthalocyanine > Co–unsubstituted phthalocyanine > Co–tetrasulfonatophthalocyanine > Co–perfluorinated phthalocyanine. Vitamin B12 exhibits the maximum activity. A correlation of log I (at constant potential) versus the Co(II)/(I) formal potential of the catalysts gives a volcano curve. This clearly shows that the search for better catalysts for this reaction point to those N4-macrocyclic complexes with Co(II)/(I) formal potentials close to −0.84 V versus SCE, which correspond to an optimum situation for the interaction of the thiol with the active site.

The aim of this study is to examine chitosan, which is a good film former, as a corrosion protective coating for AA-2024-T3 aluminium alloy. The aluminium samples were first anodized to increase adhesion of the subsequently dip coated film from a chitosan-acetic acid solution. To further increase the protective ability of the chitosan coating, the coated samples were immersed in a copper ion solution for 24 h. The copper salts used were sulphate and acetate. The chitosan membranes exposed to copper ion solutions revealed a reduced permeability in comparison with the unexposed samples, and an increase in stability in aqueous solutions, as revealed by a steady state and a high open circuit potential in borax solution. From UV-Vis spectroscopic measurement of the film on ITO glasses, the reduction in permeability of the chitosan film modified by copper ions appears to be associated with copper cross linking within the chitosan structure.

The hydrazine oxidation by iron(II) phthalocyanine (Fe(II)Pc) has been studied using an energy profile framework through quantum chemistry theoretical models calculated in the gas phase at the density functional theory B3LYP/LACVP(d) level. We applied two models of charge-transfer mechanisms previously reported (J. Phys. Chem. A 2005, 109, 1196) for the hydrazine oxidation mediated by Co(II)Pc. Model 1 consists of an alternated loss of one electron and one proton, involving anionic and neutral species. Model 2 considers an alternated loss of two electrons and two protons and includes anionic, neutral, and cationic species. Both applied models describe how the charge-transfer process occurs. In contrast with the obtained results for Co(II)Pc, we found that the hydrazine oxidation mediated by Fe(II)Pc is a fully through-bond charge-transfer mechanism. On the other hand, the use of different charge-transfer descriptors (spin density, electronic population, condensed Fukui function) showed a major contribution of the iron atom in comparison with the cobalt atom in the above-mentioned process. These results could explain the higher catalytic activity observed experimentally for Fe(II)Pc in comparison with Co(II)Pc. The applied theoretical models are a good starting point to rationalize the charge-transfer process of hydrazine oxidation mediated by Fe(II)Pc.

The electrocatalytic oxidation of sulfite ( ) in basic medium (pH = 10.2) at [Ni(II)-5,7,12,14-tetramethyldinaphtho[b,i]-1,4,8,11-tetraaza[14]annuleneH]++/glassy carbon (mono-[Ni(II)tmdnTAA]++/GC), and poly-[Ni(II)-5,7,12,14-tetramethyldinaphtho[b,i]-1,4,8,11-tetraaza[14]annuleneH]++/glassy carbon(poly-[Ni(II)tmdnTAA]++/GC) modified electrodes was investigated. Both modified electrodes were characterized by cyclic voltammetry. These modified electrodes show an important catalytic effect for sulfite oxidation mediated by the Ni(III)/Ni(II) redox couple. The potential shifted about 570 mV in cathodic direction with respect to bare Glassy carbon. The amperometric response (I pa) for sulfite oxidation at pH = 10.2 in phosphate buffer or a carbonate buffer with both modified electrodes gives a linear correlation between 0.92–1.8 mM for mono-[Ni(II)tmdnTAA]++/GC, and 0.25–1.50 mM for poly-[Ni(II)tmdnTAA]++/GC respectively.

Catalytic activity of cobalt tetra ethoxythiophene and cobalt tetra phenoxypyrrole phthalocyanine complexes towards oxidation of 2-mercaptoethanol, l -cysteine and reduced glutathione is reported. It was found that the activity of the complexes depends on the substitution of the phthalocyanine ring, pH, film thickness and method of electrode modification. The high electrocatalytic activity obtained with adsorbed complexes in alkaline medium clearly demonstrates the necessity of modifying bare carbon electrodes to endow them with the desired behaviour.

This study shows that cobalt macrocyclics, namely Co-phthalocyanine (CoPc), Co-hexadecafluorophthalocyanine (CoF16Pc), Co-octaethylhexyloxyphthalocyanine (CoOEHPc), Co-tetraaminophthalocyanine (CoTAPc) and Co-tetrasulfophthalocyanine (CoTSPc), strongly adsorbed on a graphite electrode surface, exhibit true electrocatalytic activity for the oxidation of glucose in alkaline solution. The Tafel analysis of the electrochemical process occurring at these chemically modified electrodes, that become “molecular phthalocyanine electrodes”, suggests that a first-one electron step is rate controlling with the symmetry of the energy barrier depending on the type of substituents grafted on the macrocycle. The effect of substituents on the phthalocyanine ring on the catalytic activity was analyzed and a non-linear correlation is found. The volcano-shaped plot obtained when comparing catalytic activities versus the Co(II)/(I) formal potential indicates that a narrow window of Co(II)/(I) formal potentials exists for achieving maximum activity. In the particular case of the present work, we find that the most active phthalocyanine is the unsubstituted CoPc.

Several molecular descriptors, based on topological approaches as well as on a more traditional orbital-based decomposition, have been used to asses relations with hydrogen bond strengths in a series of formic acid dimers and its sulfur derivatives. Particular attention has been devoted to the analysis of the core-valence bifurcation topological index and to the bond order index. Their values are seen to be linearly related to bond energies estimated through a bond-energy-bond-order relationship; also, the mean value of the topological index appears to be related to the complexation energy computed by methods based on density functional theory. The dependence of the index upon the donor-acceptor couple in relation to its applicability is discussed.

A theoretical study of some aniline derivatives toward corrosion of copper in hydrochloric acid was carried out using cluster models for aniline–copper surface systems and ab initio Hartree Fock calculations. This study showed that the interaction of aniline molecules is highly favored in surface defects like the corner. The adsorption energy increases in several orders of magnitude rising from 30 to 67 kcal/mol. The interaction occurs between the surface defect and the amino group of the aniline molecule. The adsorption energy increases with anilines possesing electron donor substituents and decreases with anilines possessing electron acceptor substituents. These results showed that the corrosion inhibition by aniline molecules can be associated mainly to local properties acting on highly active sites, like defects, present in the copper surface. In addition, the possibility of ion pair formation between protonated aniline and chloride ion, and its influence on the general adsorption of aniline on copper is also analyzed.

The inhibiting action of aniline and its derivatives on the corrosion of copper in hydrochloric acid has been investigated, with emphasis on the role of substituents. With this purpose five different anilines were selected: aniline, p-chloro aniline, p-nitro aniline, p-methoxy and p-methyl aniline. The electrochemical and gravimetric results, obtained in the absence and presence of different concentrations of inhibitors, revealed that aniline reduces the corrosion of copper, with a critical concentration of 10−2 M. Furthermore, the interaction energy calculated as ΔGads gave a value of 4.2 kcal mol−1 indicating physisorption of the organic compound at the copper surface. The results have also shown that substituents, either electron donors (–CH3, –OCH3) or, electron acceptors (–NO2, –Cl) in para position, decrease the inhibition action of aniline. A theoretical study using molecular mechanic and ab initio Hartree Fock methods, to model the adsorption of aniline on copper (100) showed results in good agreement with the experimental data. Aniline adsorbs parallel to the copper surface, showing no preference for a specific adsorption site. On the other hand, from ab initio Hartree Fock calculations, an adsorption energy between 2 kcal/mol and 5 kcal/mol is obtained, which is close to the experimental value, confirming that the adsorption of aniline on the metal substrate is rather weak. In view of these results, the orientation of the aniline molecule with respect to the copper surface is considered to be the dominant effect.

Thin films of polyNi(II)tetrasulfophthalocyanine (polyNiTSPc) electrodeposited on a gold electrode by potential cycling in 0.1 M NaOH solutions containing 1 mM Ni(II) tetrasulfophthalocyanine were studied by cyclic voltammetry, electrochemical quartz crystal microbalance and impedance techniques. Both the mass increase due to the electrodeposited film, and the current of the Ni(II)/Ni(III) process in the film, increase monotonically with the number of electrodeposition cycles, a linear correlation existing between these two parameters. AFM micrographs show that the film is rugose and porous, this porosity being confirmed by the fact that the voltammetric features of gold oxide formation and reduction are unaffected by the film. The cyclic voltammogram of the film in a pH 11 carbonate–hydrogencarbonate buffer shows the characteristic anodic and cathodic peaks of the Ni ( II ) ⇔ Ni ( III ) process, with a large mass decrease upon Ni(II) electrooxidation and an equally large mass increase upon Ni(III) electroreduction. The sign of the mass change is compatible with a β-Ni(OH) 2 -character of the film. The large slopes of the plots of mass change vs. charge in the Ni(II)/Ni(III) region clearly show that large fluxes of water and/or ions accompany the electron transfer. The fairly low activation energy of Ni(II) electrooxidation, 38 kJ mol −1 , is in agreement with the moderately non-Nernstian behaviour of the Ni(II)/Ni(III) process. The super-Nernstian dependence on pH of the peak potentials of the Ni(II)/Ni(III) process indicates that the species involved are non-stoichiometric, similarly to the Ni 1 − x H x (OH) 2 species in nickel hydroxide.

This study reports on the role of both electron donor and electron acceptor substituents on the periphery of phthalocyanine cycle on the electrocatalytic activity of cobalt phthalocyanines for the oxidation of 2-aminoethanethiol (2-AET). By using these groups it is possible to modulate the Co(II)/(I) formal potential of the catalysts. The reported results show that the electrocatalytic activity of the adsorbed phthalocyanines containing electron-withdrawing groups decreases as the Co(II)/(I) formal potential of the catalyst becomes more positive, while electron-donating groups on the periphery of the ligand increase the catalytic activity.