Electrochemical generation of light in conjugated polymers

Polyphenylene vinylene (PPV) and its derivatives represent the prototype systems for the realization of luminescent layers in electroluminescent LEDs. Recently they have been important in the development of light emitting electrochemical cells (LEC). The luminescent properties of the conducting polymer layer are determined by not only the chemical species constituting the conducting polymer, but also the solid electrolyte of the electrochemical cell. In the present paper is reported a kinetics study of electrochemiluminescence (ECL) produced by 4-methoxy(2'ethylhexoxyl)-2,5-poly(phenylene vinylene), denoted herein as MEH-PPV, thin coatings when different electrochemical conditions are adopted. To our knowledge this represents one of the few critical studies on the features of ECL produced by polymer modified electrodes

An EQCM study of the electrochemical copper(II)/copper(I)/copper system in the presence of PEG and chloride ions

The charge-transfer reaction between copper(II) and copper electrodes is studied in electrolytes that are similar to galvanic copper baths, 2.2 M H2SO4 + 0.3 M CuSO4 + chloride ions (cCl < 1 x 10–2 M), and polyethyleneglycol 1500 (PEG, cPEG < 4 x 10–3 M). Electrochemical quartz crystal microbalance (EQCM) measurements are conducted, mainly under conditions of cyclic voltammetry. The formation and dissolution of CuCl on the electrode surface at cCl < 2 mM is demonstrated, a notable shift of the pseudo-equilibrium potential associated with CuCl deposition is analyzed, and the inhibition of the charge-transfer reaction by the PEG/Cl– surface layer is characterized. It is shown that the inhibiting layer forms by reaction between the adsorbate-covered copper electrode and PEG, i.e., neither Cu+ nor Cu++ from the electrolyte are required. Numerical simulations of the processes as well as parallel experiments conducted with electrolytes not containing Cu(II) support the proposed mechanisms, in particular the role of the intermediate Cu+

On the mechanism of Ag(111) sub-monolayer oxidation: a combined electrochemical, in situ SERS and ex situ XPS study

In the present work in situ surface enhanced Raman spectroscopy (SERS), ex situ X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) are used to study the interface between a Ag(111) electrode and an alkaline electrolyte. Formation of a number of potential-dependent adsorbates is observed above the point of zero charge (Epzc) of the Ag electrode. These are: OH groups (OHadsγ−) and oxide-like species (Oadsδ−). Electrochemisorbed hydroxide species show by the appearance of Raman bands at 540–560 cm−1 and at 803–819 cm−1, attributed to Ag–OH stretching and AgO–H bending vibrations respectively. Strong isotope shift of the Raman bands towards lower frequencies is observed in D2O solutions, proving their assignment. The Oadsδ− and OHadsγ− species are characterised by the O 1s peaks at ca. 529.5 and 531.6, respectively. Formation of the above-mentioned species is verified also by the UP spectra of the emersed electrodes, showing the bands at 3.0 eV typical for the oxide-like adsorbates and 9.0 and 11.1 eV for hydroxo-groups. The OHadsγ− and Oadsδ− species are negatively charged, as evidenced by the adsorption of Na+ on the Ag electrode positive to the Epzc. A mechanism of the Ag(111) sub-monolayer oxidation is suggested on the basis of combined evidence from cyclic voltammetry, in situ SERS, ex situ XPS and UPS