QSPR study of passivation by phenolic compounds at platinum and boron-doped diamond electrodes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Blocking polycrystalline platinum (Pt) and boron-doped diamond (BDD) electrodes by 20 phenolic compounds was studied by means of chronoamperometric and theoretical methods [i.e., quantitative structure-property relationships (QSPRs)] and chemometric methods. The difference between the current densities after 15 and 90 s of oxidation time was proposed for the first time as a quantitative measurement of passivation on the electrodes. Structures of phenolic molecules and their hydrogen-bonding complexes with fluoride ion were modeled and geometry optimized with the B3LYP method and the 6-31G** basis set. Several molecular descriptors were calculated and correlated with the passivation measurements using the partial least-squares (PLS) regression method. A PLS model with one latent variable from five descriptors was built with high-level predictivity for phenolic passivation on the Pt electrode, and then was externally validated with four phenolics. The Pt model statistical parameters obtained were: Q(2) = 0.786, R(2) = 0.851, and standard error of validation (SEV) = 0.097. A BDD model with one latent variable and four descriptors was built and validated in the same way; however, the statistical parameters (Q(2) = 0.333, R(2) = 0.586, and SEV = 0.159) were of inferior quality with respect to the model for the Pt electrode. Both models were applied for prediction of 10 phenolic compounds. The Pt model showed to be suitable for predictive purposes. It was observed that passivation was much weaker on the BDD electrode than on the Pt electrode. Different interactions and reactions involving phenolics at the electrodes are the main reasons for such large differences between the models. Exploratory analyses were also performed and interpreted in terms of chemical concepts, such as phenolic reactivity, size/shape, hydrogen bonding, and electronic features. These findings can be useful to explore the possibility to predict phenolic passivation and to design electrochemical experiments involving different phenolic compounds. Furthermore, these PLS models aid in understanding electrode inactivation by phenolic compounds. (C) 2008 The Electrochemical Society.15510D640D650Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Improvement of the electrochemical properties of "as-grown" boron-doped polycrystalline diamond electrodes deposited on tungsten wires using ethanol

The electrochemical properties of boron-doped diamond (BDD) polycrystalline films grown on tungsten wire substrates using ethanol as a precursor are described. The results obtained show that the use of ethanol improves the electrochemistry properties of "as-grown" BDD, as it minimizes the graphitic phase upon the surface of BDD, during the growth process. The BDD electrodes were characterized by Raman spectroscopy, scanning electronic microscopy, cyclic voltammetry ( CV), and electrochemical impedance spectroscopy ( EIS). The boron-doping levels of the films were estimated to be similar to 10(20) B/cm(3). The electrochemical behavior was evaluated using the Fe(CN)(6)(3-/4-) and Ru(NH3)(6)(3-/4-) redox couples and dopamine. Apparent heterogeneous electro-transfer rate constants k(app)(0) were determined for these redox systems using the CV and EIS techniques. k(app)(0) values in the range of 0.01-0.1 cm s(-1) were observed for the Fe(CN)(6)(3-/4-) and Ru(NH3)(6)(3-/4-) redox couples, while in the special case of dopamine, a lower k(app)(0) value of 10(-5) cm s(-1) was found. The obtained results showed that the use of CH3CH2OH (ethanol) as a carbon source constitutes a promising alternative for manufacturing BDD electrodes for electroanalytical applications.11101449145