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Electrocatalytic nitrogen reduction reaction (eNRR) is a new method for sustainable NH3 production, which has attracted much attention in recent years. However, the low Faradaic efficiency due to the competitive hydrogen evolution reaction (HER) and inert N≡N triple bond activation hinders its practical application. To find highly efficient electrocatalysts with excellent activity, stability and selectivity, we have studied a series of transition metal dimers (TM2) loaded on poly triazine imide, (PTI) a crystalline carbon nitride, by density functional theory calculations. The results show that most of the metal dimers have good stability. Finally, among 26 homonuclear diatomic catalysts, Mo2@PTI, Re2@PTI, and Pt2@PTI exhibit strong capability for suppressing HER, with a favorable limiting potential of −0.53, −0.36, and −0.63 V, respectively, and hence, can be used as efficient electrocatalysts for NRR. In this study, a homonuclear diatomic eNRR catalyst was designed and screened to provide not only a theoretical basis for the experiments but also an alternative approach for sustainable synthesis of ammonia.

Density functional theory calculations have been performed to study the reaction mechanism of N2 thermal reduction (N2TR) over a single metal atom incorporated nitrogen-doped graphene. Our results reveal that the type of metal atoms and their coordination environments have a significant effect on the catalytic activity of N2TR. Regarding CoN4- and FeN4-embedded graphene sheets that the metal atom is fourfold coordinated, they are inactive for N2TR owing to the poor stability of the adsorbed H2 and N2 molecules. In contrast, if the monodisperse metal atom is surrounded by three N atoms, namely, CoN3/G and FeN3/G show activity toward N2TR, and catalytic conversion of N2 into ammonia is achieved through the associative mechanism rather than the dissociative mechanism. Further investigations show that the synthesis of NH3 over the two surfaces is mainly through the formation of an NHNH* intermediate; however, the detailed reaction mechanisms are sensitive to the type of metal atom introduced into N-doped graphene. Based on the calculated kinetic barriers, FeN3/G exhibits a better catalytic activity for N2TR. The superior performance of FeN3/G can be attributed to the fact that this surface prefers a high spin-polarized state during the whole process of N2TR, while the non-spin polarized state is predicted as the ground state for most of the elementary steps of N2-fixation over CoN3/G. The present study provides theoretical insights into developing graphene-based single atom catalysts with a high activity toward ammonia synthesis through N2TR.

The first principle calculations have been performed to investigate the geometries, band structures and optical absorptions of a series of MIL-125 MOFs, in which the 1,4-benzenedicarboxylate (BDC) linkers are modified by different types and amounts of chemical groups, including NH2, OH, and NO2. Our results indicate that new energy bands will appear in the band gap of pristine MIL-125 after introducing new group into BDC linker, but the components of these band gap states and the valence band edge position are sensitive to the type of functional group as well as the corresponding amount. Especially, only the incorporation of amino group can obviously decrease the band gap of MIL-125, and the further reduction of the band gap can be observed if the amount of NH2 is increased. Although MIL-125 functionalized by NH2 group exhibits relatively weak or no activity for the photocatalytic O2 evolution by splitting water, such ligand modification can effectively improve the efficiency in H2 production because now the optical absorption in the visible light region is significantly enhanced. Furthermore, the adsorption of water molecule becomes more favorable after introducing of amino group, which is also beneficial for the water-splitting reaction. The present study can provide theoretical insights to design new photocatalysts based on MIL-125.

A comprehensive density functional theory calculation was employed to investigate the reaction mechanism of methanol synthesis on a Co-modified Cu(100) surface via CO2 hydrogenation. The Cu(100) surface with embedded small Co clusters prepared experimentally was employed as a model system to explore the effects of Co dopant on the catalytic performance of Cu(100) surface towards CH3OH synthesis. The activation energy barriers and the reaction energies of 16 elementary surface reactions were determined. Our calculated results show that the most favorable reaction pathway for the hydrogenation of CO2 to CH3OH follows the sequence of CO2 → HCOO* →H2COO* →H2COOH* →H2CO* →H3CO* →H3COH*, and the OH* group hydrogenation to H2 O* is the rate-limiting step with an activation barrier of 112.3 kJ/mol. It is noted that, since the strength of Co–O bond is stronger than that of Cu–O bond, the introducing of Co dopant on the Cu surface can facilitate the formation of key intermediates for the CH3OH synthesis. Especially...

The structures and electronic properties of bimetallic oxide CrW2O9 clusters supported on the perfect and defective MgO(001) surfaces with three different color centers, FS (0), FS (+), and FS (2+) centers, respectively, have been investigated by density functional theory calculations. Our results show that the configurations, adsorption energies, charge transfers, and bonding modes of dispersed CrW2O9 clusters are sensitive to the charge states of the FS centers. Compared with the gas-phase configuration, the CrW2O9 clusters supported on the defective surfaces are distorted dramatically, which exhibit different chain structures. On the perfect MgO surface, the depositions of clusters do not involve obvious charge transfer, while the situation is quite different on the defective MgO(001) surfaces in which significant electron transfer occurs from the surface to the cluster. Interestingly, this effect becomes more remarkable for electron-rich oxygen vacancies (FS (0) center) than that for electron-poor oxygen vacancies (FS (+) and FS (2+) centers). Furthermore, our work reveals a progressive Brønsted acid sites where spin density preferentially localized around the Cr atoms not the W atoms for all kinds of FS-centers, indicating the better catalytic activities can be expected for CrW2O9 cluster on defective MgO(001) surfaces with respect to the W3O9 cluster.