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 NO_x 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.