In-situ developed active sites of MOFs in aqueous electrocatalytic ammoxidation

Abstract

Metal organic frameworks (MOFs) are frequently employed as electrocatalysts for chemical and energy conversions, owing to their tailored structure and electronic properties. However, the stability and evolution of MOFs under electrochemical conditions remain unclear, resulting in the identification of true active sites a challenging task, thus limiting the design of high-performance electrocatalysts. Here, we follow the development of a representative Co-MOF anode in electrolyte under bias by in-situ spectroscopies, and resolve the evolution of active species for efficient electrocatalytic ammoxidation of aldehydes. A rapid dissociation of Co-MOF occurs in KOH, forming a composite electrocatalyst (e-Co) that consists of crystalline cobalt hydroxide (Co(OH)₂) and amorphous cobalt oxide (CoO_x). The active Co²⁺ sites promote the dissociative adsorption of ammonia, forming Co³⁺-NH_3–x sites to interact with aldehyde, yielding an imine intermediate and eventually generating nitrile via dehydrogenation. The evolved e-Co electrocatalyst exhibits a satisfactory yield (83%) and Faradaic efficiency (72%) for the synthesis of nitrile at an ultra-low cell voltage of 1.0 V in aqueous electrolyte under ambient air pressure. The e-Co electrocatalyst also displays a decent stability, a broad substrate scope, and a consistent catalytic performance at higher reactant concentrations, offering a sustainable solution for ammoxidation at a practical scale.