Tunable Surface Chemistry in Heterogeneous Bilayer Single-Atom Catalysts for Electrocatalytic NOx Reduction to Ammonia

Electrochemical NOx reduction reaction (NOxRR) holds promise for both nitrogen pollution management and low-temperature ammonia (NH3) synthesis; however, it relies on catalysts with controllable reaction pathways and product selectivity. For this purpose, heterogeneous bilayer single-atom catalysts (BSACs) with tunable surface chemistry are proposed as a general design strategy in heterogeneous catalysis. For example, NOxRR on a series of bilayer N-doped graphene (G(N)) supported single-atom catalysts (denoted as M-2-CmNn-G(N)) are systematically investigated. The BSACs can not only circumvent the undesired metal aggregation and N-N coupling step, but also preserve the advantages of tunable reactivity from a dual-atom site. The intrinsic dipole moment stemming from the asymmetric structure of the heterogeneous BSACs enables enhanced local electric field around reactive sites and allows effective control of chemisorption of reaction species. Interestingly, the polarization-dependent activation of NOx greatly affects the reaction path, limiting potential, and selectivity of the NOxRR. This study highlights a universal strategy for the rational design of catalysts with high performance for NH3 electrosynthesis and beyond.