Direct Nitrile Electrosynthesis from Amino Acids on Nickel Oxyhydroxide

Abstract

The anodic oxidation of biomass coupled with cathodic hydrogen evolution reaction (HER) is one of the most promising methods to simultaneously achieve sustainable hydrogen production and value-added chemical synthesis. Amino acid, one of the most abundant biomass resources, has rarely been explored for electrochemical valorization, except for the limited studies on precious-metal-based electrodes or corrosive bromide redox. The electrochemical oxidation amino acids toward value-added chemicals on low-cost materials remains yet to be investigated. Here, we discovered that on a simple α-Ni(OH)2 pre-catalyst, a range of amino acids undergo both oxidative dehydrogenation and decarboxylation to generate valued nitriles at a low potential of 1.42 V vs. RHE, among which alanine (Ala) and glutamine (Glu) exhibited over 90% Faradaic efficiency (FE) toward nitrile. The unique NiOOH catalyst surface enabled the kinetically-favored oxidative dehydrogenation into imine, succeeded decarboxylation on the distal carboxylate via electron transfer and eventual dehydrogenation into nitriles. Moreover, we developed an in-situ extraction method for hydrophobic amino acids like lysine (Lys), to effectively increase the FE toward glutaronitrile, an important alternative to adiponitrile to sustain the nylon industry. This study not only reveals the uninvestigated oxidative decarboxylation behavior of amino acids, but also demonstrates a new promising pathway to synthesize functional nitriles from widely-accessible biomolecules.