Marcio Vidotti

Synthesis and characterization of stable Co and Cd doped nickel hydroxide nanoparticles for electrochemical applications

The present paper describes the physical-chemical characterization and electrochemical behavior of a new nanomaterial formed by the addition of cadmium and cobalt atoms into the structure of nickel hydroxide nanoparticles, these ones synthesized by an easy sonochemical method. Particles of about 5 nm diameter were obtained and characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction and Raman spectroscopy. Different nickel hydroxide nanoparticles were immobilized onto transparent conducting substrates by using electrostatic layer-by-layer providing thin films at the nanoscale and the electrochemical behavior was investigated. The formation of a mixed hydroxide was corroborated by observation of very interesting properties as redox potential shifting to less positive potentials and high stability when submitted to long electrochemical cycling or high times of ultrasonic synthesis, suggesting practical applications.

A New Sensor for Ammonia Determination Based on Polypyrrole Films Doped with Dodecylbenzenesulfonate (DBSA) Ions

Polypyrrole is the most widely used conducting polymer for sensors and biosensors construction once their conductivity and electroactivity do not strongly depend on the pH of the electrolyte. The aim of the present article is the improvement of amperometric ammonia determination, using dodecylbenzenesulfonate (DBSA) doped polypyrrole film. This large amphiphilic dopant promotes changes on the polymeric film leading to a more accentuated current and extending the linear response over a wide concentration range, when compared with films doped with small inorganic anions, such as chloride. The sensor×s response was followed by EQCM and Raman spectroscopy experiments with the aim of elucidating the mechanism of ammonia detection.

A highly efficient redox chromophore for simultaneous application in a photoelectrochemical dye sensitized solar cell and electrochromic devices

We synthesized a novel series of compounds based on a ruthenium(II) dicarboxybipyridine (dcbpy) complex containing chloro and trans-1,4-bis[2-(4-pyridyl)ethenyl]benzene (BPEB) ligands. The binuclear species Na6[{[RuII(dcbpy)2Cl}2(BPEB)] exhibits an electrochromic effect when reduced, which is assigned to the radical BPEB0/˙, similarly as in viologen-based compounds. The carboxylate groups on the 4,4′ positions of bipyridine allow a strong attachment to the TiO2 surface, contributing to an efficient and reversible electron transfer from the oxide to the chromophoric ligand, coloring the oxide film blue. The coloration efficiency CE(λ) at 633 nm was 109 cm2 C−1, which is high compared to TiO2 itself. The complex also exhibits a high photon-to-electron conversion efficiency (IPCE > 70%) when applied as a photoanode in a dye sensitized solar cell (DSSC).

“On line” mass spectrometric detection of ammonia oxidation products generated by polypyrrole based amperometric sensors

Polypyrrole (PPy) is the conducting polymer most widely employed in electrochemical sensors for ammonia detection in the last decade. Although sensors have been described in depth in the literature, the mechanism of ammonia detection by polypyrrole is still a matter of controversy. The differential electrochemical mass spectrometry (DEMS) technique, together with UV-Vis spectroscopy, gives direct and conclusive evidence with respect to the ammonia oxidation products formed in NaOH solution (pH = 10) at polyrrole or N-methyl polypyrrole film sensors polarized at 0.35 V (Ag/AgCl). Monitoring of the different possible ammonia oxidation products by on-line DEMS measurements indicates that only NO is formed and that other species such as N2 or N2O are absent. UV-Vis absorption spectroscopy also showed that ionic products such as nitrate or nitrite are not formed.

Electrochromic Properties of a Metallo-supramolecular Polymer Derived from Tetra(2-pyridyl-1,4-pyrazine) Ligands Integrated in Thin Multilayer Films

The electrochromic behavior of iron complexes derived from tetra-2-pyridyl-1,4-pyrazine (TPPZ) and a hexacyanoferrate species in polyelectrolytic multilayer adsorbed films is described for the first time. This complex macromolecule was deposited onto indium-tin oxide (ITO) substrates via self-assembly, and the morphology of the modified electrodes was studied using atomic force microscopy (AFM), which indicated that the hybrid film containing the polyelectrolyte multilayer and the iron complex was highly homogeneous and was approximately 50 nm thick. The modified electrodes exhibited excellent electrochromic behavior with both intense and persistent coloration as well as a chromatic contrast of approximately 70%. In addition, this system achieved high electrochromic efficiency (over 70 cm(2) C(-1) at 630 nm) and a response time that could be measured in milliseconds. The electrode was cycled more than 10(3) times, indicating excellent stability.