Physico-chemical principles of AC electrosynthesis

Electrolysis integrates renewable energy into chemical manufacturing and is key towards sustainable chemistry. Controlling the waveform beyond direct current (DC) addresses the long-standing obstacle of chemoselectivity, yet it also expands the parameter set to optimise, creating a demand for theoretical predictions. Here, we report the first analytical theory for predicting chemoselectivity in alternating current (AC) electrosynthesis. The mechanism is a selective reversal of the unwanted redox reaction during periods of opposite polarity, reflected in the final reaction outcome as a time-averaged effect. In the ideal scenario of all redox reactions being reversible, square AC waveform biases the outcome towards more overoxidation/overreduction, whereas sine AC waveform exhibits the opposite effect. However, in a more realistic scenario of some redox reactions being quasi-reversible, sine AC behaves mostly like square AC. These predictions are in numerical agreement with model experiments employing acetophenone and align qualitatively with literature precedent. Collectively, this study provides theoretical proof for a growing trend that promotes changing waveform to overcome limitations challenging to address by varying canonical electrochemical parameters.