Redox-mediated electrified synthesis of benzaldehyde

Abstract

Electrosynthesis is a promising approach for the green and sustainable production of valuable organic chemicals, and it is increasingly being recognized as a significant research field in chemistry. However, it is frequently plagued with challenges such as sluggish reaction kinetics, poor selectivity and low reaction yield due to the intricate electrode–electrolyte interface, limited electrode compartment space, constraints in electrocatalysts and difficulties in separating reaction products. With the oxidation of benzyl alcohol as a model reaction, we present a system that decouples the scalable synthesis of benzaldehyde from the electrode compartment to a chemical reactor. This process operates through an electrochemical–chemical cycle in a vanadium-based flow cell. It involves the electrochemical oxidation of VO²⁺ on the electrode and the chemical reduction of VO₂⁺ by benzyl alcohol on the surface of the Co₁/NC catalyst in a reactor tank, achieving oxidation to benzaldehyde with a high selectivity close to 100%. The favorable thermodynamic properties of the VO²⁺/VO₂⁺ pair prevent the formation of benzoic acid as a byproduct. Additionally, the immiscibility of the organic phase with the aqueous vanadium electrolyte facilitates the separation of the benzaldehyde product. On the counter electrode side of the cell, the above processes are paired with a V²⁺/V³⁺-mediated hydrogen evolution reaction facilitated by the MoS₂/CF catalyst in a separate reactor tank. Consequently, the decoupled synthesis of benzaldehyde and hydrogen is achieved through the operation of a vanadium flow cell, demonstrating the potential of the redox-mediated electrified approach for precise control of organic synthesis.