Solar nitrogen (N 2 ) fixation is the most attractive way for the sustainable production of ammonia (NH 3 ), but the development of a highly active, long-term stable and low-cost catalyst remains a great challenge. Current research efforts for N 2 reduction mainly focus on the metalbased catalysts using the electrochemical approach, while metalfree or solar-driven catalysts have been rarely explored. Herein, on the basis of a concept of electron "acceptance-donation", a metal-free photocatalyst, namely, boron (B) atom, decorated on the optically active graphitic-carbon nitride (B/g-C 3 N 4 ), for the reduction of N 2 is proposed by using extensive first-principles calculations. Our results reveal that gas phase N 2 can be efficiently reduced into NH 3 on B/g-C 3 N 4 through the enzymatic mechanism with a record low onset potential (0.20 V). Moreover, the B-decorated g-C 3 N 4 can significantly enhance the visible light absorption, rendering them ideal for solar-driven reduction of N 2 . Importantly, the as-designed catalyst is further demonstrated to hold great promise for synthesis due to its extremely high stability. Our work is the first report of metal-free single atom photocatalyst for N 2 reduction, offering cost-effective opportunities for advancing sustainable NH 3 production.

Nanoscale molybdenum disulfide (MoS 2 ) has attracted ever-growing interest as one of the most promising nonprecious catalysts for hydrogen evolution reaction (HER). However, the active sites of pristine MoS 2 are located at the edges, leaving a large area of basal planes useless. Here, we systematically evaluate the capabilities of 16 kinds of structural defects including point defects (PDs) and grain boundaries (GBs) to activate the basal plane of MoS 2 monolayer. Our first-principle calculations show that six types of defects (i.e., V s , V MoS3 , Mo S2 PDs; 4|8a, S bridge, and Mo−Mo bond GBs) can greatly improve the HER performance of the in-plane domains of MoS 2 . More importantly, V s and Mo S2 PDs and S bridge and 4|8a GBs exhibit outstanding activity in both Heyrovsky and Tafel reactions as well. Moreover, the different HER activities of defects are well-understood by an amendatory band-center model, which is applicable to a broad class of systems with localized defect states. Our study provides a comprehensive picture of the defect-engineered HER activities of a MoS 2 monolayer and opens a new window for optimizing the HER activity of twodimensional dichalcogenides for future hydrogen utilization.

Electrocatalytic or photocatalytic N2 reduction holds great promise for green and sustainable NH3 production under ambient conditions, where an efficient catalyst plays a crucial role but remains a long‐standing challenge. Here, a high‐throughput screening of catalysts for N2 reduction among (nitrogen‐doped) graphene‐supported single atom catalysts is performed based on a general two‐step strategy. 10 promising candidates with excellent performance are extracted from 540 systems. Most strikingly, a single W atom embedded in graphene with three C atom coordination (W1C3) exhibits the best performance with an extremely low onset potential of 0.25 V. This study not only provides a series of promising catalysts for N2 fixation, but also paves a new way for the rational design of catalysts for N2 fixation under ambient conditions.

Nanosheet supported single-atom catalysts (SACs) can make full use of metal atoms and yet entail high selectivity and activity, and bifunctional catalysts can enable higher performance while lowering the cost than two separate unifunctional catalysts. Supported single-atom bifunctional catalysts are therefore of great economic interest and scientific importance. Here, on the basis of first-principles computations, we report a design of the first single-atom bifunctional eletrocatalyst, namely, isolated nickel atom supported on β boron monolayer (Ni/β-BM), to achieve overall water splitting. This nanosheet supported SAC exhibits remarkable electrocatalytic performance with the computed overpotential for oxygen/hydrogen evolution reaction being just 0.40/0.06 V. The ab initio molecular dynamics simulation shows that the SAC can survive up to 800 K elevated temperature, while enacting a high energy barrier of 1.68 eV to prevent isolated Ni atoms from clustering. A viable experimental route for the synthesis of Ni/β-BM SAC is demonstrated from computer simulation. The desired nanosheet supported single-atom bifunctional catalysts not only show great potential for achieving overall water splitting but also offer cost-effective opportunities for advancing clean energy technology.

Developing alternatives to precious Pt for hydrogen production from water splitting is central to the area of renewable energy. This work predicts extremely high catalytic activity of transition metal (Fe, Co, and Ni) promoted two‐dimensional MXenes, fully oxidized vanadium carbides (V2CO2), for hydrogen evolution reaction (HER). The first‐principle calculations show that the introduction of transition metal can greatly weaken the strong binding between hydrogen and oxygen and engineer the hydrogen adsorption free energy to the optimal value ≈0 eV by choosing the suitable type and coverage of the promoters as well as the active sites. Strain engineering on the performance of transition metal promoted V2CO2 further reveals that the excellent HER activities can maintain well while those poor ones can be modulated to be highly active. This study provides new possibilities for cost‐effective alternatives to Pt in HER and for the application of 2D MXenes.

An efficient, earth-abundant, and low-cost catalyst for hydrogen evolution reaction (HER) is critical for sustainable hydrogen generation. In this work, we present a density-functional-theory-based screening among two-dimensional (2D) transition metal carbides (MXenes) with a fully O-terminated surface. The catalytic activity of 10 monometal carbides is first investigated, and Ti2CO2 and W2CO2 are found to be highly active catalysts for HER. Then, a volcano plot between the number of electron surface O atoms gains (N e) and the absolute value of the free energy of hydrogen adsorption (ΔG H) is established. A simple descriptor, N e, is thus proposed to evaluate the HER performance of O-terminated MXenes. On this basis, TiVCO2 is extracted with improved HER performance than Ti2CO2 and W2CO2 among 7 bimetal carbides. Our study provides new possibilities for cost-effective alternatives to Pt for HER, and, more importantly, develops a simple activity descriptor to efficiently search for highly active HER catalysts.

Defect-induced trap states are essential in determining the performance of semiconductor photodetectors. The de-trap time of carriers from a deep trap can be prolonged by several orders of magnitude as compared to shallow traps, resulting in additional decay/response time of the device. Here, it is demonstrated that the trap states in 2D ReS can be efficiently modulated by defect engineering through molecule decoration. The deep traps that greatly prolong the response time can be mostly filled by protoporphyrin molecules. At the same time, carrier recombination and shallow traps in-turn play dominant roles in determining the decay time of the device, which can be several orders of magnitude faster than the as-prepared device. Moreover, the specific detectivity of the device is enhanced (as high as ≈1.89 × 10 Jones) due to the significant reduction of  the dark current through charge transfer between ReS and molecules. Defect engineering of trap states therefore provides a solution to achieve photodetectors with both high responsivity and fast response.

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