Selective oxidation of amines to imines through electrocatalysis is an attractive and efficient way for the chemical industry to produce nitrile compounds, but it is limited by the difficulty of designing efficient catalysts and lack of understanding the mechanism of catalysis. Herein, we demonstrate a novel strategy by generation of oxyhydroxide layers on two-dimensional iron-doped layered nickel phosphorus trisulfides (Ni1−xFexPS3) during the oxidation of benzylamine (BA). In-depth structural and surface chemical characterizations during the electrocatalytic process combined with theoretical calculations reveal that Ni(1−x)FexPS3 undergoes surface reconstruction under alkaline conditions to form the metal oxyhydroxide/phosphorus trichalcogenide (NiFeOOH/Ni1−xFexPS3) heterostructure. Interestingly, the generated heterointerface facilitates BA oxidation with a low onset potential of 1.39 V and Faradaic efficiency of 53% for benzonitrile (BN) synthesis. Theoretical calculations further indicate that the as-formed NiFeOOH/Ni1−xFexPS3 heterostructure could offer optimum free energy for BA adsorption and BN desorption, resulting in promising BN synthesis.