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

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 Ni sites with Cu single atoms/clusters in a limited range of 0 to 3.6 nm. From Ni to Cu, via the hydrogen spillover process, the hydrogen radicals (H⋅) generated at the unsaturated Ni sites could migrate across HsGDY to the Cu sites to participate in the transformation of *HNO to NH. From Cu to Ni, bypassing the higher reaction energy for *HNO formation on the Ni sites, the NO detached from the Cu sites could diffuse onto the unsaturated Ni sites to form NH 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.