Efficient Electrosynthesis of Adipic Acid via a Cascade Reaction at Pickering Droplet Interfaces.

Adipic acid is currently produced via a nitric acid oxidation route, leading to substantial NOx and CO2 emissions. The sustainable adipic acid production powered by renewable electricity is highly desirable. Herein, we report an innovative strategy for efficient electrosynthesis of adipic acid by cascading a bromide-assisted olefin epoxidation and a subsequent epoxide oxidation on a Pickering-droplet-integrated electrode under ambient conditions. The oil-water interface provided by Pickering emulsion droplets on the electrode was found to be capable of stabilizing bromine radicals for facilitating the epoxidation process and simultaneously weakening the interfacial hydrogen-bonding network to suppress the competitive oxygen evolution reaction, which are crucial to activate the relatively inert C═C bonds and enhance the selectivity of epoxide oxidation. With this strategy, we achieved efficient continuous-flow adipic acid electrosynthesis with high FEs (∼80%), high selectivity (∼95%), long-term operational stability (1000 h), and scaling capability to achieve a 100 g scale synthesis at industrially relevant current densities (100 mA cm-2), using crude cyclohexene from the benzene hydrogenation as feedstock.