Atomically Precise Dinuclear Ni2 Active Site-Modified MOF-Derived ZnO@NC Heterojunction toward High-Performance N2 Photofixation

The development of heterogeneous catalysts with atom-dispersed active sites is essential to facilitate nitrogen (N-2) activation for the N-2 reduction reaction (NRR). However, it remains a major challenge to tune the coordination configuration of the metal centers to further accelerate the activation kinetics. Herein, an atomically precise dinuclear Ni-2 site-modified metal- organic framework (MOF)-derived ZnO@NC heterojunction (ZnO@NC-Ni-2) was developed for effective N-2 photofixation under mild conditions. Moreover, advanced structural character-ization indicates that the most active N-coordinated bimetallic site configurations are Ni-2-N-6, where two Ni-1-N-4 moieties are shared with two N atoms. Theoretical calculations further demonstrate that the binuclear Ni2 active sites of ZnO@NC-Ni-2 could adjust the N-2 adsorption configuration as the side-on bridging adsorption mode (denoted as "*N N*"), while the single metal Ni-1 sites of ZnO@NC-Ni-1 tend to form a terminal adsorption configuration with N-2 ("*N N" type). As a result, the unique electronic structure of binuclear Ni-2 active sites in ZnO@NC-Ni-2 tends to proceed as an associative alternating pathway, thereby decreasing the activation energy barrier of the reaction procedure and favoring the photocatalytic NRR. The present study provides a perspective to probe the relationship between the coordination architecture of earth-abundant metal active centers and NRR activities.