Physico-Chemical nanomaterials science

Electrochemical investigation of redox transitions during complexation process in Cu-Cysteine system
Vyshnevska Yu.P.1, Brazhnyk I.V.2
1 National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute".
37K20, Peremohy Ave., Kyiv, 03056, Ukraine. 
E-mail: vishnevsk@ukr.net
2 Gimasi SA.
4, Piazzale Roncàa, Mendrisio, 6850, Switzerland.

Copper NPs, nanoclusters and their hybrid nanocomposites constitute a promising basis for electrochemical and optical sensing devices, catalytic materials for various reactions including light-induced photocatalysis for hydrogen energy applications. Cysteine (Cys) provides convenient and environmental friendly CuNPs synthesis route and may serve as a multipurpose synthesis and stabilizing agent that draw high scientific interest to studying Cu-Cys system. In present report, electrochemical behavior of copper in 0.5M H2SO4 in presence of cysteine has been investigated and kinetic regularities of the complexation process in Cu-Cys system have been determined. Experimental results obtained using cyclic voltammetry (CV) method showed that after each cycle of polarization, a gradual drop in current density may be observed in the potential range of active metal dissolution that is attributed to formation of Cu-Cys complexes that affects further ionization process. On the cathodic portion of polarization scan in presence of Cys the additional current peaks may be observed compared to blank solution. Most notable change is strong prolonged wave in range 0.28-0.05V, reaching peak value at 0.15V associated with complexes discharge in addition to Cu cations discharge as well as a noticeable cathode peak near -0.15V that may be attributed with cysteine-cystine transition. It should be noted, that cyclic polarization scan performed in reverse direction (anodic after cathodic) does not show signs of such discharge processes on the first pass due to lack of metal ions and, thus, the metal-cysteine complexes which is in line with the theoretical expectations. Potentiostatic electrochemical studies for potentials 0.5, 0.4, 0.25, 0.15, 0.03, -0.19 and -0.07V coupled with the surface morphology analysis enabled to assess the time-dependant parameters for the complexation process and also confirmed that the potential range for the complexation process matches one for the potentiodynamic regime. Understanding redox states and transitions in such systems is a key for development new efficient synthesis routes for novel nanocomposite materials.