The reduction of N₂ molecules to NH₃ is a very challenging task in chemistry. The electrocatalytic nitrogen reduction reaction (NRR) is a promising technology for NH₃ synthesis. By using first-principles calculation, a new class of single-atom catalysts (SACs), graphdiyne coordinated single transition metal atoms (TM@GDY, TM = Sc–Zn, Y–Cd, and La–Hg) were designed, and the NRR catalytic character of TM@GDY was systematically investigated. The results demonstrated that some TM@GDY (TM = Ti, V, Fe, Co, Zr, Rh, and Hf) monolayers exhibit better NRR activities than a Ru(0001) stepped surface. There is an obvious linear correlation between the limiting potential and the atomic N adsorption energy, which confirms that the N adsorption energy may be a descriptor for evaluation of the NRR catalytic performance. The V@GDY monolayer possesses the best NRR catalytic character with the lowest limiting potential of −0.67 V and the potential-limiting step (PLS) of *N₂ → *NNH for both alternating and distal mechanisms. Our results highlight a new family of efficient and stable TM@GDY catalysts and provide useful guidelines for SAC development and practical applications.

The interaction of various gas molecules with a defective WSe₂ monolayer is theoretically studied. The defective WSe₂ monolayer exhibits enhanced sensing ability toward H₂O and N₂ molecules. The doping of the WSe₂ monolayer due to the interaction of CO, NO, NO₂, and N₂O molecules with Se vacancies is discussed.

Inspired by the recently discovered dynamics of single Fe atoms in graphene vacancies, we systemically examined the stable configurations, electronic structures, and catalytic activities of Fe-atom-embedded graphene substrates (including monovacancy graphene (MG) and divacancy graphene (DG)) by using first-principles calculations. We found that the doped Fe on the MG sheet (Fe/MG) is more stable than that on the DG sheet (Fe/DG). Doping with Fe atoms provides more transferred electrons to fill the vacancy defects of graphene and allows it to exhibit a more positive charge, which effectively regulates O₂ and CO adsorption. Also, the degree of interactions between the reactants and substrates are connected to the reaction pathways and energy barriers. For the Fe/MG sheet, the low coadsorption energy of gas molecules can promote the catalytic reaction through the Langmuir–Hinshelwood (LH) mechanism. In comparison, the initial step for CO oxidation on the Fe/DG sheet is through the Eley–Rideal (ER) mechanism, which is an energetically more favorable process. Moreover, the more stable Fe/MG sheet is a much more efficient catalyst for CO oxidation at low temperature, because the sequential reaction processes (LH and ER) have low enough energy barriers. These results provide valuable guidance on selecting the metal dopant in graphene materials to design effective atomic-scale catalysts.

Even the simplest point defect in a two-dimensional (2D) material can have a significant influence on its electronic, magnetic, and chemical properties. Defect repairing in 2D materials has been a focus of concern in recent years. Based on first-principles calculations, the repair of C and N single vacancies with CO or NO molecules in a C₃N monolayer has been studied. The repair process consists of two steps, i.e., filling of the vacancy with the first molecule and removal of the extra O atom by a second molecule. Overall, the repair processes of C and N single vacancies by CO or NO molecules are both thermodynamically and kinetically favorable, as evidenced by the significant energy released and the small energy barriers. In addition, the electronic and magnetic properties and the chemical activity of the C₃N monolayer before and after the defect repair have been studied systematically. In addition to single vacancies, the repair of double vacancies with CO was also studied; this process is much less kinetically favorable than the case of single vacancies. This study provides useful insight into the effects of simple atomic vacancies on the physical and chemical properties of the C₃N 2D semiconductor and also presents a promising strategy for repairing vacancies.

Graphdiyne (GDY) could provide a unique platform for synthesizing uniform single-atom catalysts (SACs) with high catalytic activity toward oxygen reduction (ORR) and oxygen evolution (OER) reactions.

Based on the density functional theory calculations, the formation geometry, electronic properties, and catalytic activity of metal impurities in divacancy graphene (M-DG, M = Mo, Fe, Co, and Ni) were systematically investigated. It has been found that the reactive gases have different stabilities on M-DG substrates, and these quite stable substrates exhibit high catalytic activity for CO oxidation by comparing the traditional Eley–Rideal (ER) and Langmuir–Hinshelwood (LH), as well as the new termolecular ER (TER) mechanisms. For the Co-DG substrate, the coadsorption of O₂ and CO as a starting step is an energetically more favorable process, whereas the dissociation reaction of O₂ molecules on Mo-DG substrate has a much smaller energy barrier, and the generation of atomic oxygen is active for CO oxidation. These results indicate that the varied adsorption behaviors of reactive gases on M-DG substrates can determine the catalytic pathways and energy barriers, which give us insight into the surface reactivity of graphene–metal composite catalysis in energy-related devices.