Theoretical and experimental study of the catalytic cathodic stripping square-wave voltammetry of chromium species

MARIELA CUÉLLAR, SABRINA N.VETTORELO,PATRICIA I.ORTIZ & FERNANDO GARAY

JOURNAL OF SOLID STATE ELECTROCHEMISTRY (PRINT)

SPRINGER

Lugar: Berlin; Año: 2016

1432-8488

The electrocatalytic mechanism of Cr(III) reductionin the presence of diethylenetriaminepentaacetic acid (DTPA)and nitrate ions is studied theoretically and experimentally byusing stripping square-wave voltammetry (SWV).Experimental curves are in excellent agreement with theoret-ical profiles corresponding to a catalytic reaction of secondkind. This type of mechanism is equivalent to a CE mecha-nism, where the chemical reaction produces the electroactivespecies. Accordingly, the reaction of Cr(III)?H2O?DTPA andNO3would produce the electroactive species Cr(III)?NO3?DTPA and this last species would release NO2to the solutionduring the electrochemical step. In this regard, the complex ofCr(III)?DTPA would work as the catalyzer that allows thereduction of NO3to NO2. Furthermore, it was found thatthe electrochemical reaction is quite irreversible, with a con-stant of ks=9.4×10−5cm s−1, while the constant for the chem-ical step has been estimated to be kchem=1.3×104s−1.Considering that the equilibrium constant is K= 0.01, it ispossible to estimate the kinetic constants of the chemical reac-tion as k1=1×102s−1and k−1=1.29×104s−1.Thesevaluesof k1and k−1indicate that the exchange of water molecules bynitrate is fast and that the equilibrium favors the complex with water. Also, a value for the formal potential E°?≈−1.1 V wasobtained. The model used for simulating experimental curvesdoes not consider the adsorption of reactants yet. Accordingly,weak adsorption of reagents should be expected.