Molecular electrochemistry and electrocatalysis: a dynamic view

Abstract

The frequent simple gross redox reaction notation, where A is a solution species and B_ads 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 B_ads. Conversely, the reaction may be a composite one involving two sequential steps. One such two-step mechanism may be termed as a C_adsE_ads sequence where C_ads stands for a pre-adsorption elementary step and E_ads for the follow-up ET. Alternatively, the two steps may proceed in the reverse order, leading to an E_solnC_ads 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.

Keywords:

• adsorption
• cyclic voltammetry
• electrocatalysis
• molecular electrochemistry
• KISSA-1D^©

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.

Additional information

Funding

This work was supported in part by CNRS, UPMC and ENS (UMR 8640 and LIA XiamENS) as well by the ANR Chaire d’Excellence ‘MicroNanoChem’ [grant number ANR-10-CHEX-012-01] and CNRS [PICS grant number 5697].