Two electrodes, many pathways: New strategies in paired organic electrosynthesis

Paired organic electrolysis has re-emerged as a compelling strategy for increasing the synthetic value, electron utilisation and energy efficiency of organic electrosynthesis. By deliberately selecting both half-reactions, paired systems can employ electric power to promote the formation of added-value products, and/or to achieve a lower cell voltage, whilst reducing their dependence on purely charge-balancing processes such as the oxygen evolution reaction (OER). Recent advances demonstrate that paired electrolysis is expanding from biomass-derived substrates and CO 2 -derived products towards recycle-derived substrates, chemically interdependent reactions and reagent electro-generation. Furanics, phenolics, carboxylates, glycerol, polymer-derived ethylene glycol and CO 2 have been exploited to access polymer precursors, C 1 and C 2 oxygenates, organic carbonates, H 2 O 2 , acrolein, ammonia and complex organic products. More chemically integrated systems have enabled convergent C-C bond formation, Shono-type oxidation/phthalide synthesis, oxime formation, cyclic amine functionalisation, nitrate-to-ammonia coupling, and in situ generation of H 2 O 2 , formaldehyde and hydroxylamine. Several reports now approach process-relevant operation through flow cells, membrane-electrode assemblies and zero-gap electrolysers, with current densities at or above 100 mA cm -2 and extended stability tests. These advances also show that productive chemistry at both electrodes is only the starting point. Successful electrochemical pairing requires compatible electron demand, reaction rate, electrode potential, electrolyte and pH conditions, limited crossover, sufficient product concentration, stable intermediates and feasible downstream processing. Herein, recent advances in paired organic electrolysis are evaluated and the criteria for selecting, operating and reporting paired systems that merit further development beyond proof-of-concept electrolysis are proposed, with an emphasis on reactor choice, cell voltage over time, product recovery, failure modes and preliminary techno-economic assessments.