The environmental instability of single‐ or few‐layer black phosphorus (BP) has become a major hurdle for BP‐based devices. The degradation mechanism remains unclear and finding ways to protect BP ...from degradation is still highly challenging. Based on ab initio electronic structure calculations and molecular dynamics simulations, a three‐step picture on the ambient degradation of BP is provided: generation of superoxide under light, dissociation of the superoxide, and eventual breakdown under the action of water. The well‐matched band gap and band‐edge positions for the redox potential accelerates the degradation of thinner BP. Furthermore, it was found that the formation of P‐O‐P bonds can greatly stabilize the BP framework. A possible protection strategy using a fully oxidized BP layer as the native capping is thus proposed. Such a fully oxidization layer can resist corrosion from water and leave the BP underneath intact with simultaneous high hole mobility.
Protected by native oxide: A three‐step picture of the ambient degradation of black phosphorus (BP) is given. A possible protection strategy using a fully oxidized BP layer as the capping is proposed. Such a fully oxidized layer can resist corrosion from water and leave the BP underneath intact with simultaneous high hole mobility.
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.
The electrochemical reduction of CO2 offers an elegant solution to the current energy crisis and carbon emission issues, but the catalytic efficiency for CO2 reduction is seriously restricted by the ...inherent scaling relations between the adsorption energies of intermediates. Herein, by combining the concept of single-atom catalysts and multiple active sites, we design heteronuclear dual-atom catalysts to break through the stubborn restriction of scaling relations on catalytic activity. Twenty-one kinds of heteronuclear transition-metal dimers are embedded in monolayer C2N as potential dual-atom catalysts. First-principles calculations reveal that by adjusting the components of dimers, the two metal atoms play the role of carbon adsorption sites and oxygen adsorption sites respectively, which results in the decoupling of adsorption energies of key intermediates. Free energy profiles demonstrate that CO2 can be efficiently reduced to CH4 on CuCr/C2N and CuMn/C2N with low limiting potentials of −0.37 V and −0.32 V, respectively. This study suggests that the introduction of multiple active sites into porous two-dimensional materials would provide a great possibility for breaking scaling relations to achieve efficient multi-intermediate electrocatalytic reactions.
Direct Z-scheme heterostructure photocatalysts possess tremendous potential to solar-driven overall water splitting, but how to rationally design and comprehensively characterize high-efficient ...direct Z-scheme heterostructures remains a great challenge. Herein, we report the design of metal-free C3B/C3N heterostructure through constructing a p-n heterojunction as a potential direct Z-scheme photocatalyst for overall water splitting by combining first-principles and excited state dynamics simulations. Our calculations show that the strong interlayer interaction in C3B/C3N p-n heterostructure provides a large built-in electric field with about 0.4 V/Å and strong interface nonadiabatic coupling which significantly accelerates the recombination of carriers with weak redox capacity (∼0.5 ps) and retards the lifetime of carriers with strong redox capacity (∼4 ps). Meanwhile, the B atoms, serving as Lewis acid sites, are good catalytic centers to trap water molecules. The hydrogen reduction reaction and complex four-electronic water oxidation reaction can happen smoothly on the C3B and C3N surface, respectively, without additional overpotential and cocatalyst. This work not only provides a potential metal-free direct Z-scheme photocatalyst for overall water splitting, but also paves the way to rational design high-performance direct Z-scheme photocatalysts.
Rapidly discovering functional materials remains an open challenge because the traditional trial-and-error methods are usually inefficient especially when thousands of candidates are treated. Here, ...we develop a target-driven method to predict undiscovered hybrid organic-inorganic perovskites (HOIPs) for photovoltaics. This strategy, combining machine learning techniques and density functional theory calculations, aims to quickly screen the HOIPs based on bandgap and solve the problems of toxicity and poor environmental stability in HOIPs. Successfully, six orthorhombic lead-free HOIPs with proper bandgap for solar cells and room temperature thermal stability are screened out from 5158 unexplored HOIPs and two of them stand out with direct bandgaps in the visible region and excellent environmental stability. Essentially, a close structure-property relationship mapping the HOIPs bandgap is established. Our method can achieve high accuracy in a flash and be applicable to a broad class of functional material design.
Nanoscale molybdenum disulfide (MoS2) has attracted ever-growing interest as one of the most promising nonprecious catalysts for hydrogen evolution reaction (HER). However, the active sites of ...pristine MoS2 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 MoS2 monolayer. Our first-principle calculations show that six types of defects (i.e., Vs, VMoS3, MoS2 PDs; 4|8a, S bridge, and Mo–Mo bond GBs) can greatly improve the HER performance of the in-plane domains of MoS2. More importantly, Vs and MoS2 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 MoS2 monolayer and opens a new window for optimizing the HER activity of two-dimensional dichalcogenides for future hydrogen utilization.
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 β12 boron monolayer (Ni1/β12-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 Ni1/β12-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.
Vertically stacked two-dimensional multilayer structures have become a promising prototype for functionalized nanodevices due to their wide range of tunable properties. In this paper we performed ...first-principles calculations to study the electronic structure of nontwisted and twisted bilayers of hybrid graphene/MoS2 (Gr/MoS2) and MoS2/MoS2. Both twisted bilayers of Gr/MoS2 and MoS2/MoS2 show significant differences in band structures from the nontwisted ones with the appearance of the crossover between direct and indirect band gap and gap variation. More interestingly, the band structures of twisted Gr/MoS2 with different rotation angles are very different from each other, while those of MoS2/MoS2 are very similar. The variation of band structure with rotation angle in Gr/MoS2 is, indeed, originated from the misorientation-induced lattice strain and the sensitive band-strain dependence of MoS2.
We systematically investigate the electronic structure and optical properties of edge-functionalized graphene quantum dots (GQDs) utilizing density functional and many-particle perturbation theories. ...A mechanism based on the competition and collaboration between frontier orbital hybridization and charge transfer is proposed. The frontier orbital hybridization of the GQD moiety and functional group reduces the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), while the charge transfer from the GQD moiety to the functional group enlarges it. Contrarily, frontier orbital hybridization and charge transfer collaborate to shift down the energy of the first bright exciton, the former through activation of low-lying dark excitons and the latter via increased exciton binding energy. Functional groups containing a carbon–oxygen double bond (CO), namely, aldehyde (−CHO), ketone (−COCH3), and carboxyl (−COOH), are more favorable for tailoring the electronic and optical properties of pristine GQD among all the functional groups investigated here. The amino group (−NH2), although frequently employed in experiments, has a much weaker influence on electronic structure since the large charge transfer cancels out the effect of frontier orbital hybridization.
Water splitting and rechargeable air-based batteries are emerging as new renewable energy storage and conversion technologies. However, the discovery of suitable catalysts with high activity and low ...cost remains a great challenge. In this work, we report a single-atom trifunctional catalyst, namely Ti3C2O2 supported single Pd atom (Pd1@Ti3C2O2), for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). This catalyst is selected from 12 candidates and possesses low overpotentials of 0.22 V, 0.31 V and 0.34 V for the HER, OER and ORR, respectively, making it an excellent electrocatalyst for both overall water splitting and rechargeable air-based batteries. The superior OER and ORR performance originates from the optimal d band center of the supported Pd atom. Moreover, the excellent activity can be maintained even if the single Pd atoms aggregate into small clusters. This work offers new opportunities for advancing the renewable energy storage and conversion technologies and paves a new way for the development of multifunctional electrocatalysts.
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