Design of Single-atom Catalysts on C5N2 for Nitrogen Fixation at Ambient Conditions : A First-principles Study.

Single atom catalysts (SACs) exhibit the flexible coordination structure of the active site and high utilization of active atoms, making them promising candidates for nitrogen reduction reaction (NRR) under ambient conditions. By the aid of first-principles calculations based on DFT, we have systematically explored the NRR catalytic behavior of thirteen 4d- and 5d-transition metal atoms anchored on 2D porous graphite carbon nitride C5N2. With high selectivity and outstanding activity, Zr, Nb, Mo, Ta, W and Re-doped C5N2 are identified as potential nominees for NRR. Particularly, Mo@C5N2 possesses an impressive low limiting potential of -0.39 V (corresponding to a very low temperature and atmospheric pressure), featuring the potential determining step involving *N-N transitions to *N-NH via the distal path. The catalytic performance of TM@C5N2 can be well characterized by the adsorption strength of intermediate *N2H. Moreover, there exists a volcanic relationship between the catalytic property UL and the structure descriptor Ψ, which validates the robustness and universality of Ψ, combined with our previous study. This work sheds light on the design of SACs with eminent NRR performance.

HER catalytic activity and regulation of a transition metal atom-anchored BC3 monolayer: a first-principles study.

An atomic-level understanding of the hydrogen evolution reaction (HER) on a transition metal (TM) atom-anchored 2D monolayer is vital to explore highly efficient catalysts for hydrogen production. Here, the catalytic activities and modulation of TM atom (Ti, Fe, Cu, Zn, Mo, Ag, Au)-doped BC3 monolayers are investigated by first-principles calculations. Au@BC3 and Fe@BC3 are proven to be potentially excellent HER catalysts. Partial oxidation engineering on Zn@BC3 could improve its performance. Au@BC3 and Ti, Cu and Mo-anchored BC3 with the support of a NbB2 (0001) surface are expected to replace Pt due to the Gibbs free energy changes extremely close to zero. It is revealed that the catalytic activity of the adsorption site is highly related to the degree of charge transfer between the adsorption site and substrate.

Two-dimensional ternary pentagonal BCX (X = P, As, and Sb): promising photocatalyst semiconductors for water splitting with strong piezoelectricity.

Seeking high-performance energy conversion materials is one of the most important issues in designing 2D materials. In the framework of density functional theory, we propose a series of ternary monolayers, penta-BCX (X = P, As, and Sb), and systematically investigate their structural stability, mechanical, piezoelectric, and photocatalytic properties. All three materials are semiconductors with a bandgap ranging from 2.56 eV to 3.24 eV, so they could be promising catalysts for the photolysis of water. Penta-BCX exhibits significant piezoelectric properties attributed to their non-centrosymmetric structure and low in-plane Young's modulus, which are expected to efficiently drive photocatalytic water decomposition. Moreover, the bandgap, band edge position, and light absorption of penta-BCX can be modulated by tensile or compressive strain to enhance their photocatalytic performance in the visible light and ultraviolet regions.

Prediction of 2D IV-V semiconductors: flexible monolayers with tunable band gaps and strong optical absorption as water-splitting photocatalysts.

Seeking novel photocatalysts for water splitting is one of the tasks in developing 2D materials. In the framework of density functional theory, we predict a family of 2D pentagonal sheets called penta-XY2 (X = Si, Ge, and Sn; Y = P, As, and Sb), and modulate their properties via strain engineering. Penta-XY2 monolayers exhibit flexible and anisotropic mechanical properties, due to their low in-plane Young's modulus in the range of 19-42 N m-1. All six XY2 sheets are semiconductors with a band gap ranging from 2.07 eV to 2.51 eV, and the positions of their conduction and valence band edges match well with the reaction potentials of H+/H2 and O2/H2O, so they are suitable for photocatalytic water splitting. Under tensile/compression strains, the band gaps, band edge positions and light absorption of GeAs, SnP2 and SnAs2 could be tuned to improve their photocatalytic performance.

Charge-controlled switchable CO2 capture and gas separation using BC3 nanosheets.

The technique of CO2 capture and separation using charge-modulated sorbent materials holds promise for reducing CO2 emissions. Density functional theory with long-range dispersion correction has been used to study the adsorption of CO2, H2, CH4, and N2 on BC3 nanosheets with/without charge injections. We find that CO2 is weakly adsorbed on pristine BC3, but injection of 3 negative charges (3 e) can change the adsorption to chemical adsorption. Removing the charge results in the release of CO2 without any energy barrier. A high capacity of 4.30 × 1014 cm-2 can be achieved with 5 e charge injection, and CO2 molecules could automatically desorb after charge removal. Additionally, negatively charged BC3 exhibits high selectivity for separating CO2 from other industrial gases such as CH4, H2, and N2. Our findings provide useful guidance for the development of switchable CO2 capture and storage materials.

In silico design of single transition metal atom anchored defective boron carbide monolayers as high-performance electrocatalysts for the nitrogen reduction reaction.

Development of low-cost and high-efficiency single atom catalysts (SACs) is essential for catalyzing nitrogen reduction reactions (NRR) under ambient conditions. Current SACs suffer from low selectivity and poor activity, making it hard for them to meet the requirements of industrial applications. Here, we present a graphene-like BC3 monolayer as a substrate for single metal atoms. The catalytic performance of 4d and 5d metal atoms anchored in a vacancy containing BC3 monolayer for NRR is systematically investigated by first-principles calculations. We find that Re@VB is outstanding among all candidates, exhibiting high catalytic activity and selectivity, with a low limiting potential of -0.28 V. A new descriptor involving the active site and its environment is proposed, which has a volcano relationship with several factors in the catalytic process, establishing a link between the intrinsic properties of the active site and the catalytic performance. This study opens a new route to designing efficient catalysts with BC3 as a substrate.

Computational screening of single transition-metal atoms anchored to g-C9N4 as catalysts for N2 reduction to NH3.

The electrocatalytic nitrogen reduction reaction (NRR) is considered to be the most desirable strategy for ammonia production but still faces many challenges in terms of high activity and high selectivity. Based on density functional theory (DFT) calculations, the catalytic performance of a series of (3d, 4d and 5d series) transition metals atoms (TMs) anchored on a novel graphitic carbon-nitrogen (g-C9N4) monolayer has been systematically investigated. We find that TMs can bind tightly to g-C9N4 and form single-atom catalysts (SACs) with high thermodynamic stability. The four candidates, Nb, Ta, W and Re@g-C9N4, not only exhibit high NRR catalytic activity but also effectively inhibit the competitive HER. Among them, Nb@g-C9N4 is the most promising NRR catalyst with a lowest limiting potential of -0.21 V. The optimal reaction path for Nb, W and Re@g-C9N4 is via the enzymatic mechanism, while Ta@g-C9N4 tends to be through the distal mechanism. In addition, the decomposition potential of the g-C9N4 monolayer is higher than the limiting potential of all four SACs, ensuring the feasibility of the experimental implementation. This work identifies efficient NRR catalysts and provides a feasible screening scheme.

Phthalo-carbonitride nanosheets as excellent N2 reduction reaction electrocatalysts: a first-principles study.

Based on density functional theory computation, a series of transition metal atoms anchored on phthalo-carbonitride (pc-C3N2) nanosheets have been investigated for the nitrogen reduction reaction (NRR). The results show that Mo and W atoms anchored on the large holes of pc-C3N2 exhibit excellent performance in the NRR with low limiting potentials of -0.24 V and -0.23 V, respectively. Moreover, W@pc-C3N2 can effectively suppress the hydrogen evolution reaction. We predict that the porous carbon-nitrogen catalyst W@pc-C3N2 has a promising future to explore more favorable applications for the NRR.

Theoretical study of SnS2encapsulated in graphene as a promising anode material for K-ion batteries.

Rechargeable batteries with superior electronic conductivity, large capacity, low diffusion barriers and moderate open circuit voltage have attracted amount attention. Due to abundant resources and safety, as well as the high voltage and energy density, potassium ion batteries (KIBs) could be an ideal alternative to next-generation of rechargeable batteries. Based on the density functional theory calculations, we find that the SnS2monolayer expands greatly during the potassiumization, which limits its practical application. The construction of graphene/SnS2/graphene (G/SnS2/G) heterojunction effectively prevents SnS2sheet from deformation, and enhances the electronic conductivity. Moreover, the G/SnS2/G has not only a high theoretical special capacity of 680 mAh g-1, but an ultra-low K diffusion barrier (0.08 eV) and an average open circuit voltage (0.22 V). Our results predict that the G/SnS2/G heterostructure could be used as a promising anode material for KIBs.

Single metal atom anchored on a CN monolayer as an excellent electrocatalyst for the nitrogen reduction reaction.

Based on first-principles calculations, we have studied the behavior of single-atom catalysts formed by a series of single metal atoms (from Ti to Cu) and a CN monolayer in nitrogen reduction reactions (NRRs). It was demonstrated that TM atoms could be anchored on CN and Ti@CN has good electrical conductivity, high stability and good catalytic performance. The onset potential of Ti@CN is as low as -0.38 V through the enzymatic mechanism, which well suppresses the competitive hydrogen evolution reaction. In addition, the determinate step of Ti@CN for the N2 reduction reaction is lower than that of the Ru(0001) stepped surface (-0.98 V). We further examine the effect of coordination on activity and propose a single Ti atom anchored on CN as a promising catalyst with high catalytic capability for N2 reduction to NH3. Our work offers a new opportunity and useful guidance for the NRR in an ambient environment.