Cooperative Single-Atom Active Centers for Attenuating the Linear Scaling Effect in the Nitrogen Reduction Reaction.

Cooperative effects of adjacent active centers are critical for single-atom catalysts (SACs) as active site density matters. Yet, how it affects scaling relationships in many important reactions such as the nitrogen reduction reaction (NRR) is underexplored. Herein we elucidate how the cooperation of two active centers can attenuate the linear scaling effect in the NRR through a first-principle study on 39 SACs comprised of two adjacent (∼4 Å apart) four N-coordinated metal centers (MN duo) embedded in graphene.

Cooperative Nitrogen Activation and Ammonia Synthesis on Densely Monodispersed Mo-N-C Sites.

The production of ammonia from nitrogen reduction reaction (NRR) under mild conditions is one of the most challenging issues in modern chemistry. The linear scaling relationship between the adsorption energies of -NH and -NH on a single active site is a well-established bottleneck. By investigating a series of densely monodispersed Mo-N-C sites embedded in graphene using first-principles calculations, we found that previously underappreciated neighboring effects between adjacent active sites may help break the limit: they not only improve the energetics of potential determining steps of NRR but also promote an alternative associative mechanism based on a cooperative bridge-on adsorption of N by two Mo-N-C sites of ∼6 Å apart.

Impact of Active Site Density on Oxygen Reduction Reactions Using Monodispersed Fe-N-C Single-Atom Catalysts.

Exploring the impact of active site density on catalytic reactions is crucial for reaching a more comprehensive understanding of how single-atom catalysts work. Utilizing density functional theory calculations, we have systematically investigated the neighboring effects between two adjacent Fe-N-C sites of monodispersed Fe-N-C single-atom catalysts on oxygen reduction reaction (ORR). While the thermodynamic limiting potential () is strongly dependent on the intersite distance and the nature of adjacent active sites in FeN, it is almost invariable in FeN until two FeN sites are ∼4 Å apart.

Cooperative Spin Transition of Monodispersed FeN Sites within Graphene Induced by CO Adsorption.

The significance of identifying the fundamental mechanism of interactions between adjacent catalytic active centers has long been underestimated. Utilizing density functional theory calculations, we demonstrate controllable cooperative interaction between two nearby Fe centers embedded on nitrogenated graphene aided by CO adsorption. The interconnected adjacent Fe atoms respond cooperatively to CO molecules with communicative structural self-adaption and electronic transformation.

Strong current polarization and perfect negative differential resistance in few-FeN-embedded zigzag graphene nanoribbons.

Ferromagnetic devices have special significance in spintronics. Here, we investigate the electronic structures and transport properties of the experimentally achievable FeN-embedded armchair and zigzag graphene nanoribbons (FeN-AGNR and FeN-ZGNR). The first principles results show that FeN induces room-temperature stable ferromagnetic ground states in both AGNRs and ZGNRs, but only significant changes in the band structure of the latter, inducing strong current polarization (nearly 100%) and spin-dependent negative differential resistance (NDR) in the FeN-ZGNR based devices.

Uniform and perfectly linear current-voltage characteristics of nitrogen-doped armchair graphene nanoribbons for nanowires.

Metallic nanowires with desired properties for molecular integrated circuits (MICs) are especially significant in molectronics, but preparing such wires at a molecular level still remains challenging. Here, we propose, from first principles calculations, experimentally realizable edge-nitrogen-doped graphene nanoribbons (N-GNRs) as promising candidates for nanowires. Our results show that edge N-doping has distinct effects on the electronic structures and transport properties of the armchair GNRs and zigzag GNRs (AGNRs, ZGNRs), due to the formation of pyridazine and pyrazole rings at the edges.

Conversion of Dinitrogen to Ammonia by FeN3-Embedded Graphene.

Nitrogen fixation is one of the most important issues but a long-standing challenge in chemistry. Here, we propose FeN3-embedded graphene as the catalyst for nitrogen fixation from first-principles calculations. Results show that in view of the chemical coordination, the FeN3 center is highly spin-polarized with a localized magnetic moment substantially to promote N2 adsorption and activate its inert N-N triple bond.