Guangtao Yu

High-Index Faceted Ni3S2 Nanosheet Arrays as Highly Active and Ultrastable Electrocatalysts for Water Splitting

Elaborate design of highly active and stable catalysts from Earth-abundant elements has great potential to produce materials that can replace the noble-metal-based catalysts commonly used in a range of useful (electro)chemical processes. Here we report, for the first time, a synthetic method that leads to in situ growth of {2̅10} high-index faceted Ni3S2 nanosheet arrays on nickel foam (NF). We show that the resulting material, denoted Ni3S2/NF, can serve as a highly active, binder-free, bifunctional electrocatalyst for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Ni3S2/NF is found to give ∼100% Faradaic yield toward both HER and OER and to show remarkable catalytic stability (for >200 h). Experimental results and theoretical calculations indicate that Ni3S2/NFs excellent catalytic activity is mainly due to the synergistic catalytic effects produced in it by its nanosheet arrays and exposed {2̅10} high-index facets.

Coupling Mo2C with Nitrogen-Rich Nanocarbon Leads to Efficient Hydrogen-Evolution Electrocatalytic Sites

In our efforts to obtain electrocatalysts with improved activity for water splitting, meticulous design and synthesis of the active sites of the electrocatalysts and deciphering how exactly they catalyze the reaction are vitally necessary. Herein, we report a one-step facile synthesis of a novel precious-metal-free hydrogen-evolution nanoelectrocatalyst, dubbed Mo2 C@NC that is composed of ultrasmall molybdenum carbide (Mo2 C) nanoparticles embedded within nitrogen-rich carbon (NC) nanolayers. The Mo2 C@NC hybrid nanoelectrocatalyst shows remarkable catalytic activity, has great durability, and gives about 100 % Faradaic yield toward the hydrogen-evolution reaction (HER) over a wide pH range (pH 0-14). Theoretical calculations show that the Mo2 C and N dopants in the material synergistically co-activate adjacent C atoms on the carbon nanolayers, creating superactive nonmetallic catalytic sites for HER that are more active than those in the constituents.

Hydrogenation: a simple approach to realize semiconductor-half-metal-metal transition in boron nitride nanoribbons.

The intriguing electronic and magnetic properties of fully and partially hydrogenated boron nitride nanoribbons (BNNRs) were investigated by means of first-principles computations. Independent of ribbon width, fully hydrogenated armchair BNNRs are nonmagnetic semiconductors, while the zigzag counterparts are magnetic and metallic. The partially hydrogenated zigzag BNNRs (using hydrogenated BNNRs and pristine BNNRs as building units) exhibit diverse electronic and magnetic properties: they are nonmagnetic semiconductors when the percentage of hydrogenated BNNR blocks is minor, while a semiconductor-->half-metal-->metal transition occurs, accompanied by a nonmagnetic-->magnetic transfer, when the hydrogenated part is dominant. Although the half-metallic property is not robust when the hydrogenation ratio is large, this behavior is sustained for partially hydrogenated zigzag BNNRs with a smaller degree of hydrogenation. Thus, controlling the hydrogenation ratio can precisely modulate the electronic and magnetic properties of zigzag BNNRs, which endows BN nanomaterials many potential applications in the novel integrated functional nanodevices.

Electronic Structure and Reactivity of Boron Nitride Nanoribbons with Stone-Wales Defects.

Gradient-corrected density functional theory (DFT) computations were performed to investigate the geometry, electronic property, formation energy, and reactivity of Stone-Wales (SW) defects in zigzag-edge and armchair-edge boron nitride nanoribbons (BNNRs). The formation energies of SW defects increase with an increase in the widths of BNNRs and are orientation-dependent. SW defects considerably reduce the band gaps of BNNRs independent of the defect orientations. In addition, the local chemical reactivity of SW defects and edge sites in zigzag-edge and armchair-edge BNNRs was probed with the CH2 cycloaddition reaction. Independent of the nanoribbon types and the SW defect orientations, the reactions at SW defect sites are more exothermic than those at the center of perfect BNNRs, and the newly formed B-B and N-N bonds are the most reactive sites, followed by the 5-7 ring fusions.

Doping the Alkali Atom: An Effective Strategy to Improve the Electronic and Nonlinear Optical Properties of the Inorganic Al12N12 Nanocage

Under ab initio computations, several new inorganic electride compounds with high stability, M@x-Al12N12 (M = Li, Na, and K; x = b66, b64, and r6), were achieved for the first time by doping the alkali metal atom M on the fullerene-like Al12N12 nanocage, where the alkali atom is located over the Al-N bond (b66/b64 site) or six-membered ring (r6 site). It is revealed that independent of the doping position and atomic number, doping the alkali atom can significantly narrow the wide gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) (EH-L = 6.12 eV) of the pure Al12N12 nanocage in the range of 0.49-0.71 eV, and these doped AlN nanocages can exhibit the intriguing n-type characteristic, where a high energy level containing the excess electron is introduced as the new HOMO orbital in the original gap of pure Al12N12. Further, the diffuse excess electron also brings these doped AlN nanostructures the considerable first hyperpolarizabilities (β0), which are 1.09 × 10(4) au for Li@b66-Al12N12, 1.10 × 10(4), 1.62 × 10(4), 7.58 × 10(4) au for M@b64-Al12N12 (M = Li, Na, and K), and 8.89 × 10(5), 1.36 × 10(5), 5.48 × 10(4) au for M@r6-Al12N12 (M = Li, Na, and K), respectively. Clearly, doping the heavier Na/K atom over the Al-N bond can get the larger β0 value, while the reverse trend can be observed for the series with the alkali atom over the six-membered ring, where doping the lighter Li atom can achieve the larger β0 value. These fascinating findings will be advantageous for promoting the potential applications of the inorganic AlN-based nanosystems in the new type of electronic nanodevices and high-performance nonlinear optical (NLO) materials.

Alkali metal atom‐aromatic ring: A novel interaction mode realizes large first hyperpolarizabilities of M@AR (M = Li, Na, and K, AR = pyrrole, indole, thiophene, and benzene)

Several new electride compounds M@pyrrole (M = Li, Na, and K), Li@AR (AR = indole, thiophene, and benzene), Li@tryptophan and Li@serotonin were designed and investigated, which exhibit considerably large first hyperpolarizabilities (β0) (6705, 1116, 11399, 5781, 4808, 1536, 8106, and 9389 au, respectively) by comparison with their corresponding sole molecules pyrrole (β0 = 30 au), indole (104 au), thiophene (6 au), benzene (0 au), tryptophan (159 au) and serotonin (151 au), respectively. The computational results revealed that the interaction of the alkali metal atom with π‐conjugated aromatic ring (AR) is one effectively new approach to produce diffuse excess electron to get a large β0 value, which is advantageous for the design of the novel high‐performance NLO materials with π‐conjugated AR: alkali metal atoms doped nanomaterials and biomolecules.

Highly Active, Nonprecious Electrocatalyst Comprising Borophene Subunits for the Hydrogen Evolution Reaction

Developing nonprecious hydrogen evolution electrocatalysts that can work well at large current densities (e.g., at 1000 mA/cm2: a value that is relevant for practical, large-scale applications) is of great importance for realizing a viable water-splitting technology. Herein we present a combined theoretical and experimental study that leads to the identification of α-phase molybdenum diboride (α-MoB2) comprising borophene subunits as a noble metal-free, superefficient electrocatalyst for the hydrogen evolution reaction (HER). Our theoretical finding indicates, unlike the surfaces of Pt- and MoS2-based catalysts, those of α-MoB2 can maintain high catalytic activity for HER even at very high hydrogen coverage and attain a high density of efficient catalytic active sites. Experiments confirm α-MoB2 can deliver large current densities in the order of 1000 mA/cm2, and also has excellent catalytic stability during HER. The theoretical and experimental results show α-MoB2s catalytic activity, especially at large current densities, is due to its high conductivity, large density of efficient catalytic active sites and good mass transport property.

The Effects of the Formation of Stone–Wales Defects on the Electronic and Magnetic Properties of Silicon Carbide Nanoribbons: A First‐Principles Investigation

Detailed first-principles density functional theory (DFT) computations were performed to investigate the geometries, the electronic, and the magnetic properties of both armchair-edged silicon carbide nanoribbons (aSiCNRs) and zigzag-edged silicon carbide nanoribbons (zSiCNRs) with Stone-Wales (SW) defects. SW defects in the center of aSiCNRs can remarkably reduce their band gaps, irrespective of the orientation of the defect, whereas zSiCNRs with SW defects in the center or at the edges exhibit degenerate energies of their ferromagnetic (FM) and antiferromagnetic (AFM) states, in which metallic and half-metallic behavior can be observed, respectively; half-metallic behavior can even be observed in both the FM and AFM states simultaneously. Further, it was shown that the formation energies of the SW defects in SiCNRs are orientation dependent, and the formation of edge defects is always favored over the formation of interior defects in zSiCNRs. The possible existence of SW defects in SiCNRs was further validated through exploring the kinetic process of their formation. These findings can be anticipated to provide valuable information in promoting the potential applications of SiC-based nanomaterials in multifunctional and spintronic nanodevices.

Successive hydrogenation starting from the edge(s): an effective approach to fine-tune the electronic and magnetic behaviors of SiC nanoribbons

Based on first-principles computations, the geometries, stabilities, electronic and magnetic properties of fully and partially hydrogenated silicon carbide nanoribbons (SiCNRs) were investigated. Independent of the ribbon width, the fully hydrogenated zigzag and armchair SiCNRs are all non-magnetic wide-band-gap semiconductors. By hydrogenating zigzag SiCNRs (zSiCNRs) from the edge(s) step by step, we have constructed partially hydrogenated zSiCNRs that can be viewed as the combination of hydrogenated and pristine zigzag SiC chain building blocks along the periodical direction. The computed results reveal that greatly enriched electronic and magnetic properties can be achieved in zSiCNRs: the transition of the antiferromagnetic spin gapless semiconductor (SGS)–ferromagnetic metal–antiferromagnetic half-metal–non-magnetic semiconductor can be achieved by controlling the hydrogenation pattern and ratio. Notably, this is the first time that the concept of successive hydrogenation starting from the edge(s) is proposed as an effective approach to fine-tune the electronic and magnetic behaviors of SiCNRs. These appealing features, especially the diverse electronic and magnetic transitions, in the unitary SiCNR-based nanostructures may provide tremendous potential applications for integrated multi-functional and spintronic nanodevices.

Dihalogen edge-modification: an effective approach to realize the half-metallicity and metallicity in zigzag silicon carbon nanoribbons

By means of first-principles computations, we have systematically investigated the electronic and magnetic properties of the zSiCNR with not only homogeneous but also heterogeneous diatomic edge-modification by employing halogen atoms, where one edge is saturated by double halogen F/Cl atoms, and the other is terminated by single or double F/Cl/H atoms, respectively. The computed results reveal that this kind of edge-modification by dihalogen atoms can break the magnetic degeneracy of the pristine zSiCNR, and the intriguing electronic and magnetic behaviors invoking not only the antiferromagnetic (AFM) metallicity but also the AFM half-metallicity and ferromagnetic (FM) half-metallicity can be achieved. The decorated atoms at the C-edge of zSiCNR can play an important role in affecting the electronic and magnetic properties of the modified zSiCNR systems, and the heterogeneous asymmetric edge-modification by the halogen/hydrogen pair with great electronegative difference can more effectively strengthen the robustness of half-metallicity. Additionally, employing strong electron-withdrawing halogen atom to perform a diatomic edge-modification can also significantly lower the edge formation energy of the modified zSiCNR systems, endowing them with higher structural stability. Obviously, diatomic edge-modification with halogen atoms can be an effective strategy to modulate the electronic and magnetic behaviors of zSiCNRs, which can be of benefit in promoting excellent SiC-based nanomaterials in the application of spintronics and multifunctional nanodevices.