Red Carbon Mediated Formation of Cu2O Clusters Dispersed on the Oxocarbon Framework by Fehling's Route and their Use for the Nitrate Electroreduction in Acidic Conditions

The oligomers of carbon suboxide, known as red carbon, exhibit a highly conjugated structure and semiconducting properties. Upon mild heat treatment, it transforms into a carbonaceous framework rich in oxygen surface terminations, called oxocarbon. In this study, the abundant oxygen functionalities are harnessed as anchors to create oxocarbon‐supported nanohybrid electrocatalysts. Starting with single atomic Cu (II) strongly coordinated to oxygen atoms on red carbon, the Fehling reaction leads to the formation of Cu2O clusters. Simultaneously, a covalent oxocarbon framework emerges via cross‐linking, providing robust support for Cu2O clusters. Notably, the oxocarbon support effectively stabilizes Cu2O clusters of very small size, ensuring their high durability in acidic conditions and the presence of ammonia. The synthesized material exhibits a superior electrocatalytic activity for nitrate reduction under acidic electrolyte conditions, with a high yield rate of ammonium (NH4+) at 3.31 mmol h−1 mgcat−1 and a Faradaic efficiency of 92.5% at a potential of −0.4 V (vs RHE). Herein, Cu2O clusters are obtained dispersedly on the oxocarbon framework after the Fehling's‐like reaction during the mild annealing process of red carbon, leading to the reduction of Cu (II) predominantly to Cu2O. The covalent oxocarbon framework improves the stability of clusters, enabling their efficient nitrate electroreduction under acidic electrolytes with a high yield rate and Faradaic efficiency.