Selective electrooxidation of primary amines over a Ni/Co metal-organic framework derived electrode enabling effective hydrogen production in the membrane-free electrolyzer

The overall water electrolysis always needs an ion-conductive membrane to separate the generated hydrogen and oxygen from the corresponding cathode and anode, which improves the manufacturing cost of the electrolyzer. The substitution of thermodynamically more favorable organic oxidation reactions for oxygen evolution reaction avoids the requirement of the membrane, accompanied by the generation of value-added products at the anode. Herein, with the help of the bimetallic Ni/Co metal-organic framework derivative (t-Ni/Co MOF) as the anodic electrocatalyst, we develop an oxidant-free condition for the selective conversion of primary amines into nitriles. Specifically, aromatic and aliphatic nitriles can be conveniently obtained with good yields and faradaic efficiencies over the t-Ni/Co MOF electrode when coupling with the hydrogen evolution reaction. Notably, benzylamine can be oxidized into benzonitrile even at an ultralow potential of 1.30 V vs. reversible hydrogen electrode (RHE) over the t-Ni/Co MOF electrode, which is lower than that of the reported Ni-based monometallic electrocatalysts for benzylamine elecrooxidation. Control experiments suggest that the reversible electron transfer process of Co2+ ↔ Co3+ at a relatively low potential contributes to the formation of higher valence Ni species, which accelerates the kinetics of the primary amine oxidation, simultaneously reducing power consumption for hydrogen production.