Density Functional Theory Study of Triple Transition Metal Cluster Anchored on the C2N Monolayer for Nitrogen Reduction Reactions.

The electrochemical nitrogen reduction reaction (NRR) is an attractive pathway for producing ammonia under ambient conditions. The development of efficient catalysts for nitrogen fixation in electrochemical NRRs has become increasingly important, but it remains challenging due to the need to address the issues of activity and selectivity. Herein, using density functional theory (DFT), we explore ten kinds of triple transition metal atoms (M3 = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) anchored on the C2N monolayer (M3-C2N) as NRR electrocatalysts. The negative binding energies of M3 clusters on C2N mean that the triple transition metal clusters can be stably anchored on the N6 cavity of the C2N structure. As the first step of the NRR, the adsorption configurations of N2 show that the N2 on M3-C2N catalysts can be stably adsorbed in a side-on mode, except for Zn3-C2N. Moreover, the extended N-N bond length and electronic structure indicate that the N2 molecule has been fully activated on the M3-C2N surface. The results of limiting potential screen out the four M3-C2N catalysts (Co3-C2N, Cr3-C2N, Fe3-C2N, and Ni3-C2N) that have a superior electrochemical NRR performance, and the corresponding values are -0.61 V, -0.67 V, -0.63 V, and -0.66 V, respectively, which are smaller than those on Ru(0001). In addition, the detailed NRR mechanism studied shows that the alternating and enzymatic mechanisms of association pathways on Co3-C2N, Cr3-C2N, Fe3-C2N, and Ni3-C2N are more energetically favorable. In the end, the catalytic selectivity for NRR on M3-C2N is investigated through the performance of a hydrogen evolution reaction (HER) on them. We find that Co3-C2N, Cr3-C2N, Fe3-C2N, and Ni3-C2N catalysts possess a high catalytic activity for NRR and exhibit a strong capability of suppressing the competitive HER. Our findings provide a new strategy for designing NRR catalysts with high catalytic activity and selectivity.

Screening Multi-layered Two-dimensional Cd-chalcogenide Structures as Potential Candidates for Photocatalysis.

In recent years, clean and sustainable energy generation by photocatalytic water splitting has gained enormous attention from researchers. Two-dimensional Cd-based structures play a central role in the research of semiconductor-based photocatalysis. Here, a few layers of cadmium monochalcogenides (CdX; X=S, Se, and Te) are theoretically investigated using density functional theory (DFT). For their potential applicability in photocatalysis, it is proposed that they are exfoliated from the wurtzite structure with an electronic gap that depends on the thickness of the proposed systems. Our calculations address a long-standing doubt about the stabilities of free-standing CdX monolayers (ML). Induced buckling removes the acoustic instabilities in 2D planar hexagonal CdX structures (due to interlayer interactions) that depend on the number of neighboring atomic layers present. All studied (and stable) systems have an electronic gap of >1.68 eV, calculated with hybrid functionals (HSE06). A band-edge alignment plot about the water's oxidation-reduction potential is constructed, and a potential energy surface is constructed for the hydrogen evolution reaction. Our calculations suggest that the chalcogenide site is most favorable for hydrogen adsorption, and the energy barrier falls within the experimentally achievable limits.