Cyclic square wave voltammetry of electrode reactions with nonunity stoichiometry

A general and easy-to-manage analytical theory is presented for the square wave voltammetry (SWV) of reversible electrode reactions with complex stoichiometry, aO + ne− ⇌ bR, at macroelectrodes valid for any value of the stoichiometric and diffusion coefficients of the redox species. A comprehensive study of the SWV in cyclic mode is performed, investigating the effect of all the key variables for different stoichiometries a:b stoichiometries. As reported in literature, these reactions are of interest in the electrochemistry of hydrogen, halides and mercury complexes, among others. The concentration-dependence of the position of the SWV signal along with the peak height, width and symmetry are demonstrated to be sensitive to the reaction stoichiometry, offering rapid and simple diagnostic clues. Then, the quantitative analysis of the peak current, peak potential and half-peak width with the theory here presented allows for the determination of the stochiometric coefficients and number of electrons transferred. Also, the diffusion coefficients of the oxidized and reduced species and/or the formal potential of the redox couple can be extracted. For this, accurate procedures are proposed on the basis of simple explicit equations and working curves, proving the remarkable value of the SWV method.