Photoelectrochemical Oxidation of Amines to Imines and Production of Hydrogen through Mo-Doped BiVO4 Photoanode

Abstract

Imines are important multifunctional intermediates for the synthesis of pesticides, pharmaceuticals, biologics, and fine chemicals. The direct photoelectrochemical (PEC) oxidation of amines to imines is a highly selective, efficient, green, and gentle method. Interestingly, the constructive merging of the PEC oxidation of amines with the production of hydrogen can accelerate hydrogen evolution due to the less challenging oxidation of amines such as benzylamine (BN) in comparison to sluggish water oxidation. Herein, Mo-doped BiVO4 photoanodes were prepared and first applied to simultaneously oxide benzylamine (BN) to N-benzylidenebenzylamine (BI) and produce hydrogen in a closed two-chamber, three-electrode PEC cell After illumination at a bias of 1.3 V vs SCE for 3 h, the 3% Mo-doped BiVO4 photoanode achieved a maximum yield of ∼94 μmol h–1 at a 1 × 1 cm2 area with a BN to BI selectivity of almost 100% and a Faradaic efficiency of 98.4%. Our electrode presented enhanced photocorrosion resistance in acetonitrile solvent. Additionally, the PEC oxidations of benzylamine derivatives with different substituents (−F, −Cl, −Br, −CH3, −OCH3) to the corresponding imines were also investigated. The results indicated that the Mo-doped BiVO4 photoanode exhibited an excellent performance in the oxidation of these benzylamine derivatives with corresponding amine to imine selectivities of almost 100% and Faradaic efficiencies of >95%.