Modulation of the Second-Beyond Coordination Structure in Single-Atom Electrocatalysts for Confirmed Promotion of Ammonia Synthesis

Although microenvironments surrounding single-atom catalysts (SACs) have been widely demonstrated to have a remarkable effect on their catalytic performances, it remains unclear whether the local structure beyond the secondary coordination shells works as well or not. Herein, we employed a series of metal–organic frameworks (MOFs) with well-defined and tunable second-beyond coordination spheres as model SAC electrocatalysts to discuss the influence of long-distance structure on the ammonia synthesis from nitrate, which were synthesized and denoted as Cu 12 -NDI-X (X = NMe 2, H, F). It is first experimentally confirmed that the remote substitution of function groups beyond the secondary coordination sphere can remarkably affect the activity of ammonia synthesis. Meanwhile, the -H endowed Cu 12 -NND-H exhibits a superior ammonia yield (35.1 mg·h –1 ·mg cat –1 ) and FE (98.7%) to those modified with -NMe 2 and -F, which also shows good stability at 100 mA·cm –2 . The remarkable promotion of the modulated second-beyond coordination structure is unraveled to result from the adjustable d -band center of the Cu active site leading to promoted adsorption of the NO 3 – and protonation of key intermediates. Encouraged by its extraordinary ammonia yield, we employed the Cu 12 -NND-H electrode as a cathode to assemble one rechargeable Zn-nitrate battery that exhibits an impressive power density of 34.0 mW·cm –2, demonstrating its promising application in energy conversion and storage.