Sequential Paired Electrolysis: Challenges and Recent Developments

Sequential paired electrolysis, where substrate is converted to intermediate at one electrode and into final product at opposite electrode, is a powerful tool for (redox-neutral) single-cell cascade reactions. In this opinion, we highlight three key challenges for sequential transformations and discuss practical solutions for overcoming these obstacles based on the recent literature. First, we describe how electron mismatch between half-reactions may limit theoretical current efficiencies and require the utilization of additional counter reactions. Second, we examine how interelectrode mass transport of reactive intermediates can hinder both reaction rates and yields, especially for short-lived radical species. Flow-microreactors or interdigitated electrodes are discussed as alternative cell designs to improve mass transfer, whereas rapid alternating polarity can be used to circumvent this requirement altogether. Third, we address how low intermediate concentration and its depletion at the second electrode may present challenges for process intensification. In addition to the design of electrochemical cells and applied waveforms, the use of redox mediators can provide means for improving space-time yields.