Abstract
The frequent simple gross redox reaction notation, where A is a solution species and Bads is its adsorbed reduction product, is misleading in its simplicity. It may represent a concerted reaction, i.e., a true elementary step in which the electron transfer (ET) to the solution species A is concerted with the creation of the electrode-species bond(s) in Bads. Conversely, the reaction may be a composite one involving two sequential steps. One such two-step mechanism may be termed as a CadsEads sequence where Cads stands for a pre-adsorption elementary step and Eads for the follow-up ET. Alternatively, the two steps may proceed in the reverse order, leading to an EsolnCads mechanism in which A is reduced into B, both being solution species, followed by adsorption of B onto the electrode.
The present theoretical investigations show that a different panel of voltammetric behaviours may be produced by each mechanism. Hence, rationalising voltammetric peak positions and shapes in terms of surface or potential effects is challenging and may be completely erroneous if the wrong mechanistic sequence is considered.
Acknowledgements
Dedicated to Professor Pierre Turq on the occasion of his 70th birthday. Beyond being an esteemed and respected dear friend and colleague for three of us, one of us (C. Amatore) still remembers that during his student time, Pierre, then his teacher, played a strong influential role on his decision to pursue towards an academic career. It seems that, as usual, Pierre's guesses and intuition may have been correct.