Direct nitrile electrosynthesis from amino acids on nickel oxyhydroxide

Abstract

The anodic oxidation of biomass coupled with a cathodic hydrogen evolution reaction (HER) is a promising method to simultaneously achieve sustainable hydrogen production and value-added chemical synthesis. Amino acids are abundant biomass resources. They have rarely been explored for electrochemical valorization, except for the limited studies on precious metal-based electrodes or corrosive bromide redox reactions. The electrochemical oxidation of amino acids towards value-added chemicals on low-cost materials has not been investigated. Herein, we discovered that on a simple α-Ni(OH)₂ pre-catalyst, a range of amino acids underwent 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) towards 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 such as lysine (Lys) to effectively increase the FE toward glutaronitrile, an important alternative to adiponitrile to sustain the nylon industry. This study revealed the uninvestigated oxidative decarboxylation behavior of amino acids, but also demonstrated a new promising pathway to synthesize functional nitriles from widely accessible biomolecules.