Bridging Nickel‐MOF and Copper Single Atoms/Clusters with H‐Substituted Graphdiyne for the Tandem Catalysis of Nitrate to Ammonia

Abstract

Interfacial engineering of synergistic catalysts is one of the keys to achieving multiple proton‐coupled electron transfer processes in nitrate‐to‐ammonia conversion. Herein, by joining ultrathin nickel‐based metal‐organic framework (denoted Ni‐MOF) nanosheets with few‐layered hydrogen‐substituted graphdiyne‐supported copper single atoms and clusters (denoted HsGDY@Cu), a tandem catalyst of Ni‐MOFs@HsGDY@Cu with dual‐active interfaces was developed for the concerted catalysis of nitrate‐to‐ammonia. In such a system, the sandwiched HsGDY layer could serve as a bridge to connect the coordinated unsaturated Ni2+ sites with Cu single atoms/clusters in a limited range of 0 to 3.6 nm. From Ni2+ to Cu, via the hydrogen spillover process, the hydrogen radicals (H·) generated at the unsaturated Ni2+ sites could migrate across HsGDY to the Cu sites to participate in the transformation of *HNO3 to NH3. From Cu to Ni2+, bypassing the higher reaction energy for *HNO3 formation on the Ni2+ sites, the NO2− detached from the Cu sites could diffuse onto the unsaturated Ni2+ sites to form NH3 as well. The combined results make this hybrid a tandem catalyst with dual active sites for the catalysis of nitrate‐to‐ammonia conversion with improved Faradaic efficiency at lower overpotentials.