Ex situ electro-organic synthesis: A method to decouple electro- and thermochemical steps for unrestricted reaction control

Classic in situ electro-organic synthesis with substrates added into electrolyzers often suffers from poor efficiency and restricted product selectivity tuning possibilities. The reason is that electrolysis conditions must balance requirements of both electro- and thermochemical steps during electrocatalytic reaction cascades, and additionally compromise between paired anode and cathode reactions. Hence, selective and efficient electrosynthesis remains challenging for many products, and particularly for economic co-production of anodic and cathodic products. Herein, we exemplify the method of ex situ electro-organic synthesis as an option to break such traditional compatibility barriers. The two-step process platform separates electrochemical catalyst activation steps in time and space from thermochemical substrate conversion at the activated catalyst. Thereby, ex situ electro-organic synthesis enables independent tuning of electrochemistry and organic synthesis for unique selectivity. For proof-of-concept, we demonstrate this using redox energy storage in Ni(OH)2/NiOOH anodes for selective alcohol oxidation. Specifically, in a two-step process, first bulk oxidation of Ni(OH)2 electrodes to NiOOH material is paired to H2 production by alkaline water electrolysis. Then, “charged” NiOOH electrodes are removed from the electrolyzer and used in external vessels to exemplarily oxidize benzyl alcohol under regeneration of Ni(OH)2 for another run. Free choice of reaction medium allows to convert benzyl alcohol either to benzoic acid with 99% selectivity (in water) or to benzaldehyde with 91% selectivity (in n-hexane), where classic in situ electrolysis can only produce the acid together with H2. Since NiOOH can mediate many organic conversions, this work may inspire future electro-synthesis of several previously inaccessible products.