Oxygen reduction reaction (ORR) in alkaline solution catalysed by an atomically precise catalyst based on a Pd(II) complex supported on multi-walled carbon nanotubes (MWCNTs). Electrochemical and structural considerations.

A new atomically precise, single-ion catalyst (MWCNT-LPd) for ORR (oxygen reduction reaction), consisting of a Pd(II) complex of a tetraazacycloalkane anchored on multiwalled carbon nanotubes, has been prepared through a supramolecular approach ensuring a uniform distribution of catalytic centres on the support surface. A tetraazacycloalkane was chosen to saturate the four coordination sites of the typical square planar coordination geometry of Pd(II) with the aim of ascertaining whether the metal ion must have free coordination sites to function effectively in the ORR or whether, as predicted by quantum mechanical calculations, the catalytic effect can be originated from an interaction of O2 in the fifth coordinative position. The results clearly demonstrated that tetracoordination of Pd(II) does not influence its catalytic capacity in the ORR. Electrodes based on this catalyst show ORR performance very close to that of commercial Pt electrodes, despite the low Pd(II) content (1.72% by weight) in the catalyst. The onset potential (Eon) value and the half-wave potential (E1/2) of the catalyst are, respectively, only 53 mV and 24 mV less positive than those observed for the Pt electrode and direct conversion of O2 to H2O reaches 85.0%, compared to 89% of the Pt electrode. Furthermore, a preliminary galvanostatic test (simulating a working fuel cell at a fixed potential) showed that the catalyst maintains its efficiency continuing to produce water throughout the process (the average number of electrons exchanged over time per O2 molecule remains close to 4).

Chiral "doped" MOFs: an electrochemical and theoretical integrated study.

This work reports on the electrochemical behaviour of Fe and Zn based metal-organic framework (MOF) compounds, which are "doped" with chiral molecules, namely: cysteine and camphor sulfonic acid. Their electrochemical behaviour was thoroughly investigated via "solid-state" electrochemical measurements, exploiting an "ad hoc" tailored experimental set-up: a paste obtained by carefully mixing the MOF with graphite powder is deposited on a glassy carbon (GC) surface. The latter serves as the working electrode (WE) in cyclic voltammetry (CV) measurements. Infrared (IR), X-ray diffraction (XRD) and absorbance (UV-Vis) techniques are exploited for a further characterization of the MOFs' structural and electronic properties. The experimental results are then compared with DFT based quantum mechanical calculations. The electronic and structural properties of the MOFs synthesized in this study depend mainly on the type of metal center, and to a minor extent on the chemical nature of the dopant.

Analytic procedure for the evaluation of copper intermetallic diffusion in electroplated gold coatings with energy dispersive X-ray microanalysis.

A method for the determination of the intermetallic diffusion coefficient in the Cu-Au system is described based on energy dispersive X-ray techniques. XRF and EDS analysis were used to measure the thickness of the electroplated gold coating and the copper diffused through it, respectively. This information was used to obtain the diffusion coefficient through an equation based on Fick's law. Colour measurements and metallographic section analysis of the samples were also performed to evaluate alternative methods for a qualitative determination of diffusion rate. The thickness of the gold layer was chosen in agreement with what is used in decorative and functional applications (<1 µm). The measurements were performed on samples heated in a range of temperatures between 100 °C and 200 °C from 12 to 96 h. The results obtained follow a linear trend between the logarithm of the diffusion coefficient and the inverse of the temperature and are in line with the values found in the literature.

Specific ion effects on copper electroplating.

The main goal of this work is to open new perspectives in the field of electrodeposition and provide green alternatives to the electroplating industry. The effect of different anions (SO42-, ClO3-, NO3-, ClO4-, BF4-, PF6-) in solution on the electrodeposition of copper was investigated. The solutions, containing only the copper precursor and the background electrolyte, were tailored to minimize the environmental impact and reduce the use of organic additives and surfactants. The study is based on electrochemical measurements carried out to verify that no metal complexation takes place. We assessed the nucleation and growth mechanism, we performed a morphological characterization through scanning electron microscopy and deposition efficiency by measuring the film thickness through X-ray fluorescence spectroscopy. Significant differences in the growth mechanism and in the morphology of the electrodeposited films, were observed as a function of the background electrolyte.

A systematic study of pulse and pulse reverse plating on acid copper bath for decorative and functional applications.

Today industrial electroplating is mainly carried out using direct current even if the use of modulated currents could offer greats opportunities. Adjusting the amplitude and length of the current's pulses it is possible to control grain size, porosity and homogeneity of the deposits; the use of modulated currents could also decrease the environmental impact of deposition processes as they require a much lower percentage of organic additives. The aim of this work is to assess, through both theoretical and experimental investigation, how the deposition parameters affect the various characteristics of the deposit. We used a commercial acid copper bath for the depositions performing both pulse and reverse pulse sequences. The coatings have been characterised by estimating the deposition yield, homogeneity, hardness and reflectivity. Using pulsed currents, we obtained shinier and brighter films respect to those produced with stationary currents; the deposition efficiency was also improved. Bipolar currents, on the other hand, favour more homogeneous deposits over the entire deposition area, and are less affected by the edge effect.

On the Dynamics of the Carbon-Bromine Bond Dissociation in the 1-Bromo-2-Methylnaphthalene Radical Anion.

This paper studies the mechanism of electrochemically induced carbon-bromine dissociation in 1-Br-2-methylnaphalene in the reduction regime. In particular, the bond dissociation of the relevant radical anion is disassembled at a molecular level, exploiting quantum mechanical calculations including steady-state, equilibrium and dissociation dynamics via dynamic reaction coordinate (DRC) calculations. DRC is a molecular-dynamic-based calculation relying on an ab initio potential surface. This is to achieve a detailed picture of the dissociation process in an elementary molecular detail. From a thermodynamic point of view, all the reaction paths examined are energetically feasible. The obtained results suggest that the carbon halogen bond dissociates following the first electron uptake follow a stepwise mechanism. Indeed, the formation of the bromide anion and an organic radical occurs. The latter reacts to form a binaphthalene intrinsically chiral dimer. This paper is respectfully dedicated to Professors Anny Jutand and Christian Amatore for their outstanding contribution in the field of electrochemical catalysis and electrosynthesis.

The Fundamental and Underrated Role of the Base Electrolyte in the Polymerization Mechanism. The Resorcinol Case Study.

The Kane-Maguire polymerization mechanism is disassembled at a molecular level by using DFT-based quantum mechanical calculations. Resorcinol electropolymerization is selected as a case study. Stationary points (transition states and intermediate species) leading to the formation of the dimer are found on the potential energy surface (PES), and elementary reactions involved in the dimer formation are characterized. The latter allow to further propagate the polymerization chain reaction, when applied recursively. In this paper, the fundamental role of the sulfate anion (a typical base electrolyte) is addressed. Investigation of the PES in terms of both stationary-state properties and of ab initio molecular dynamics results (dynamic reaction coordinate) allows the appreciation in detail of the critical role of the base electrolyte anion in making the proton dissociation from the initial radical ion, a feasible (downhill in energy) process.

Influence of Chiral Compounds on the Oxygen Evolution Reaction (OER) in the Water Splitting Process.

Results are presented concerning the influence on the water splitting process of enantiopure tartaric acid present in bulk solution. Stainless steel and electrodeposited nickel are used as working electrode (WE) surface. The latter is obtained by electrodeposition on the two poles of a magnet. The influence and role played by the chiral compound in solution has been assessed by comparing the current values, in cyclic voltammetry (CV) experiments, recorded in the potential range at which oxygen evolution reaction (OER) occurs. In the case of tartaric acid and nickel WE a spin polarization of about 4% is found. The use of the chiral environment (bulk solution) and ferromagnetic chiral Ni electrode allows for observing the OER at a more favorable potential: About 50 mV (i.e., a cathodic, less positive, shift of the potential at which the oxygen evolution is observed).