Experimentally Harnessing Electric Fields in Chemical Transformations

Chemical reactivity is governed by the movement and transfer of electrons, which can in turn be steered with electric fields. With this consideration in mind, reactions are generally separated into two groups: redox and non-redox processes. The rate of a redox reaction responds dramatically to changes in voltage: relatively small biases applied between a working electrode and a suitable reference electrode can result in a current increase by as much as a factor of 10. These redox currents are in proportion to changes in the rate at which electrons are exchanged at an electrified interface, and they reflect the relative position of the available energy levels of electrode and molecule undergoing oxidation and reduction.

The effect of an external-electric field (EEF) on the rates, selectivity, and equilibrium positions of non-redox reactions can be equally dramatic. Moreover, as will be discussed in this chapter, these effects can manifest in completely different environments and experimental settings. The specific source of the EEF acting on a chemical system can range from a nanoscale gap of a scanning tunnelling microscope, to ionic aggregates, the air–water surface of a nebulised water droplet, or the interface between electrodes and electrolytes. As discussed in Chapter 2, electrostatic effects on bonding and reactivity arise because formally covalent species can be stabilised via charge-separated resonance contributors. An appropriately oriented EEF can enhance the stability of ionic structures, thereby increasing the resonance stabilisation of the bond. Chapter 2 outlines this theory in detail, and provides guidelines to predict and maximise such effects.