Modulating Electronic Structure by Etching Strategy to Construct NiSe2 /Ni0.85 Se Heterostructure for Urea-Assisted Hydrogen Evolution Reaction.

Exploring and developing novel strategies for constructing heterostructure electrocatalysts is still challenging for water electrolysis. Herein, a creative etching treatment strategy is adopted to construct NiSe2 /Ni0.85 Se heterostructure. The rich heterointerfaces between NiSe2 and Ni0.85 Se emerge strong electronic interaction, which easily induces the electron transfer from NiSe2 to Ni0.85 Se, and tunes the charge-state of NiSe2 and Ni0.85 Se. In the NiSe2 /Ni0.85 Se heterojunction nanomaterial, the higher charge-state Ni0.85 Se is capable of affording partial electrons to combine with hydrogen protons, inducing the rapid formation of H2 molecule. Accordingly, the lower charge-state NiSe2 in the NiSe2 /Ni0.85 Se heterojunction nanomaterial is more easily oxidized into high valence state Ni3+ during the oxygen evolution reaction (OER) process, which is beneficial to accelerate the mass/charge transfer and enhance the electrocatalytic activities towards OER. Theoretical calculations indicate that the heterointerfaces are conducive to modulating the electronic structure and optimizing the adsorption energy toward intermediate H* during the hydrogen evolution reaction (HER) process, leading to superior electrocatalytic activities. To expand the application of the NiSe2 /Ni0.85 Se-2h electrocatalyst, urea is served as the adjuvant to proceed with the energy-saving hydrogen production and pollutant degradation, and it is proven to be a brilliant strategy.

Modulating metal-support interaction and inducing electron-rich environment of Ni2P NPs by B atoms incorporation for enhanced hydrogen evolution reaction performance.

Modulation of the electronic interaction between the metal and support has been verified as a feasible strategy to improve the electrocatalytic performance of supported-type catalysts. Here, we have successfully synthesized an electrocatalyst of Ni2P nanoparticles (NPs) anchored on B, N co-doped graphite-like carbon nanosheets (Ni2P@B, N-GC), and elucidated the main mechanism by which B atoms doping enhances electrocatalytic hydrogen evolution reaction (HER) performance. The B atoms with electron-rich characteristic not only modulate the electronic structure on carbon skeleton, but also regulate the interfacial electronic interaction between Ni2P NPs and the carbon skeleton, which can lead to the increased available electron density of Ni sites. Such optimization is conducive to accelerating proton transfer and promoting reactive activity. As revealed, the Ni2P@B, N-GC catalyst with B atoms doping exhibits superior performance to the Ni2P@N-GC catalyst in acidic, neutral and alkaline medias. In addition, the assembled Ni(OH)2@B, N-GC||Ni2P@B, N-GC electrolyzer displays prominent overall water splitting performance in alkaline solution, which only demands 1.57 V to reach 10 mA/cm2, and in complicated natural seawater electrolyte, as low as 1.59 V. Hence, the B atoms doping strategy shows the significant enhancement for HER electrocatalysis.

Constructing abundant interfaces by decorating MoP quantum dots on CoP nanowires to induce electronic structure modulation for enhanced hydrogen evolution reaction.

Interface engineering is a method of enhancing catalytic activity while maintaining a material's surface properties. Thus, we explored the interface effect mechanism via a hierarchical structure of MoP/CoP/Cu3P/CF. Remarkably, the heterostructure MoP/CoP/Cu3P/CF demonstrates an outstanding overpotential of 64.6 mV at 10 mA cm-2 with a Tafel slope of 68.2 mV dec-1 in 1 M KOH. DFT calculations indicate that the MoP/CoP interface in the catalyst exhibited the most favorable H* adsorption characteristics (-0.08 eV) compared to the pure phases of CoP (0.55 eV) and MoP (0.22 eV). This result can be attributed to the apparent modulation of electronic structures within the interface domains. Additionally, the CoCH/Cu(OH)2/CF‖MoP/CoP/Cu3P/CF electrolyzer demonstrates excellent overall water splitting performance, achieving 10 mA cm-2 in 1 M KOH solution with a modest voltage of only 1.53 V. This electronic structure adjustment via interface effects provides a new and efficient approach to prepare high-performance hydrogen production catalysts.

Enabling Stable Zn Anodes by Molecularly Engineering the Inner Helmholtz Plane with Amphiphilic Dibenzenesulfonimide Additive.

The notorious dendrite growth and hydrogen evolution reaction (HER) are considered as main barriers that hinder the stability of the Zn-metal anode. Herein, molecular engineering is conducted to optimize the inner Helmholtz plane with a trace of amphiphilic dibenzenesulfonimide (BBI) in an aqueous electrolyte. Both experimental and computational results reveal that the BBI- binds strongly with Zn2+ to form {Zn(BBI)(H2 O)4 }+ in the electrical double layer and reduces the water supply to the Zn anode. During the electroplating process, {Zn(BBI)(H2 O)4 }+ is "compressed" to the Zn anode/electrolyte interface by Zn2+ flow, and accumulated and adsorbed on the surface of the Zn anode to form a dynamic water-poor inner Helmholtz plane to inhibit HER. Meanwhile, the{Zn(BBI)(H2 O)4 }+ on the Zn anode surface possesses an even distribution, delivering uniform Zn2+ flow for smooth deposition without Zn dendrite growth. Consequently, the stability of the Zn anode is largely improved with merely 0.02 M BBI- to the common electrolyte of 1 M ZnSO4 . The assembled Zn||Zn symmetric cell can be cycled for more than 1180 h at 5 mA cm-2 and 5 mA h cm-2 . Besides, the practicability in Zn||NaV3 O8 ·1.5 H2 O full cell is evaluated, which suggests efficient storage even under a high mass loading of 12 mg cm-2 .

Recent advances in interface engineering of Fe/Co/Ni-based heterostructure electrocatalysts for water splitting.

Among various methods of developing hydrogen energy, electrocatalytic water splitting for hydrogen production is one of the approaches to achieve the goal of zero carbon emissions. It is of great significance to develop highly active and stable catalysts to improve the efficiency of hydrogen production. In recent years, the construction of nanoscale heterostructure electrocatalysts through interface engineering can not only overcome the shortcomings of single-component materials to effectively improve their electrocatalytic efficiency and stability but also adjust the intrinsic activity or design synergistic interfaces to improve catalytic performance. Among them, some researchers proposed to replace the slow oxygen evolution reaction at the anode with the oxidation reaction of renewable resources such as biomass to improve the catalytic efficiency of the overall water splitting. The existing reviews in the field of electrocatalysis mainly focus on the relationship between the interface structure, principle, and principle of catalytic reaction, and some articles summarize the performance and improvement schemes of transition metal electrocatalysts. Among them, few studies are focusing on Fe/Co/Ni-based heterogeneous compounds, and there are fewer summaries on the oxidation reactions of organic compounds at the anode. To this end, this paper comprehensively describes the interface design and synthesis, interface classification, and application in the field of electrocatalysis of Fe/Co/Ni-based electrocatalysts. Based on the development and application of current interface engineering strategies, the experimental results of biomass electrooxidation reaction (BEOR) replacing anode oxygen evolution reaction (OER) are discussed, and it is feasible to improve the overall electrocatalytic reaction efficiency by coupling with hydrogen evolution reaction (HER). In the end, the challenges and prospects for the application of Fe/Co/Ni-based heterogeneous compounds in water splitting are briefly discussed.

Dual Atoms (Fe, F) Co-Doping Inducing Electronic Structure Modulation of NiO Hollow Flower-Spheres for Enhanced Oxygen Evolution/Sulfion Oxidation Reaction Performance.

Heteroatoms Fe, F co-doped NiO hollow spheres (Fe, F-NiO) are designed, which simultaneously integrate promoted thermodynamics by electronic structure modulation with boosted reaction kinetics by nano-architectonics. Benefiting from the electronic structure co-regulation of Ni sites by introducing Fe and F atoms in NiO , as the rate-determined step (RDS), the Gibbs free energy of OH* intermediates (ΔGOH* ) for Fe, F-NiO catalyst is significantly decreased to 1.87 eV for oxygen evolution reaction (OER) compared with pristine NiO (2.23 eV), which reduces the energy barrier and improves the reaction activity. Besides, densities of states (DOS) result verifies the bandgap of Fe, F-NiO(100) is significantly decreased compared with pristine NiO(100), which is beneficial to promote electrons transfer efficiency in electrochemical system. Profiting by the synergistic effect, the Fe, F-NiO hollow spheres only require the overpotential of 215 mV for OER at 10 mA cm-2 and extraordinary durability under alkaline condition. The assembled Fe, F-NiO||Fe-Ni2 P system only needs 1.51 V to reach 10 mA cm-2 , also exhibits outstanding electrocatalytic durability for continuous operation. More importantly, replacing the sluggish OER by advanced sulfion oxidation reaction (SOR) not only can realize the energy saving H2 production and toxic substances degradation, but also bring additional economic benefits.

Amorphous K-Buserite Microspheres for High-Performance Aqueous Zn-Ion Batteries and Hybrid Supercapacitors.

Aqueous Zn-ion batteries (AZIBs) and Zn-ion hybrid supercapacitors (AZHSCs) are considered promising energy-storage alternatives to Li-ion batteries due to the attractive merits of low-price and high-safety. However, the lack of suitable cathode materials always hinders their large-scale application. Herein, amorphous K-buserite microspheres (denoted as K-MnOx ) are reported as cathode materials for both AZIBs and AZHSCs, and the energy-storage mechanism is systematically revealed. It is found that K-MnOx is composed of rich amorphous K-buserite units, which can irreversibly be transformed into amorphous Zn-buserite units in the first discharge cycle. Innovatively, the transformed Zn-buserite acts as active materials in the following cycles and is highly active/stable for fast Zn-diffusion and superhigh pseudocapacitance, enabling the achievement of high-efficiency energy storage. In the AZIBs, K-MnOx delivers 306 mAh g-1 after 100 cycles at 0.1 A g-1 with 102% capacity retention, while in the AZHSCs, it shows 515.0/116.0 F g-1 at 0.15/20.0 A g-1 with 92.9% capacitance retention at 5.0 A g-1 after 20 000 cycles. Besides, the power/energy density of AZHSCs device can reach up to 16.94 kW kg-1 (at 20 A g-1 )/206.7 Wh kg-1 (at 0.15 A g-1 ). This work may provide some references for designing next-generation aqueous energy-storage devices with high energy/power density.

Waste-Coffee-Derived Activated Carbon as Efficient Adsorbent for Water Treatment.

Activated carbon prepared from waste coffee was utilized as a potential low-cost adsorbent to remove Rhodamine B from aqueous solution. A series of physical characterizations verify that the obtained activated carbon possesses a layered and ordered hexagonal structure with a wrinkled and rough surface. In addition, high specific surface area, appropriate pore distribution, and desired surface functional groups are revealed, which promote the adsorption properties. Various adsorption experiments were conducted to investigate the effect on the absorption capacity (e.g., of initial dye concentration, temperature and solution pH) of the material. The results showed that the waste-coffee-derived activated carbon with a large surface area of approximately 952.7 m2 g-1 showed a maximum uptake capacity of 83.4 mg g-1 at the pH of 7 with the initial dye concentration of 100 mg L-1 under 50°C. The higher adsorption capacity can be attributed to the strong electrostatic attraction between the negatively charged functional groups in activated carbon and the positively charged functional groups in RB. The kinetic data and the corresponding kinetic parameters were simulated to evaluate the mechanism of the adsorption process, which can fit well with the highest R2. The adsorption results confirmed the promising potential of the as-prepared waste-coffee-derived activated carbon as a dye adsorbent.

Trace Amount of NiP2 Cooperative CoMoP Nanosheets Inducing Efficient Hydrogen Evolution.

As a very attractive clean energy, hydrogen has a high energy density and great potential to achieve zero pollution emission. Therefore, the preparation of hydrogen evolution electrocatalysts with excellent performance is an urgent task to ameliorate the global energy shortage and environmental pollution. Here, a trace amount of NiP2 coupled with CoMoP nanosheets (NCMP) was synthesized by the one-step hydrothermal method and low-temperature phosphidation. Studies have found that although the dosage of NiP2 is very low, its appearance has been efficient to improve the hydrogen evolution reaction (HER) performance of CoMoP, which may be induced by the synergistic effect of the two different components NiP2 and CoMoP. To find the superior catalyst, the effect of Ni content on the catalyst performance is also studied, and it is found that when the dosage of Ni is 0.02 mM, NCMP-2 (2 means 0.02 mM) displays the most outstanding overpotential (10 mA cm-2) of 46 mV.

3D Hollow Quasi-Graphite Capsules/Polyaniline Hybrid with a High Performance for Room-Temperature Ammonia Gas Sensors.

Designing sensing materials with novel morphologies and compositions is eminently challenging to achieve high-performance gas sensor devices. Herein, an in situ oxidative polymerization approach is developed to construct three-dimensional (3D) hollow quasi-graphite capsules/polyaniline (GCs/PANI) hierarchical hybrids by decorating protonated PANI on the surface of GCs; as a result, an immensely active and sensitive material was developed for sensing ammonia gas at room temperature. Moreover, the GCs possessed a capsule-like hollow/open structure with partially graphitized walls, and PANI nanospheres were uniformly decorated on the GC surfaces. Furthermore, the inflexible and rigid 3D ordered chemistry of these materials provides the resulting hybrids with a large interfacial surface area, which not only allows for rapid adsorption and charge transfer but also provides the necessary structural stability. The 3D hollow GCs/PANI hybrids exhibit excellent performance; the GCs/PANI-3 hybrid is highly sensitive (with a response value of 1.30) toward 10 ppm NH3 gas and has short response and recovery times of 34 and 42 s, respectively. The GCs/PANI-3 hybrid also demonstrates a good selectivity, repeatability, and long-term stability, which are attributed to the substantial synergistic effect of the GCs and PANI. The design of such a unique 3D ordered framework provides a promising pathway to achieve room-temperature gas sensors for commercial applications.

Interfacial Charge Transfer in MoS2/TiO2 Heterostructured Photocatalysts: The Impact of Crystal Facets and Defects.

One of the most challenging issues in photocatalytic hydrogen evolution is to efficiently separate photocharge carriers. Although MoS2 loading could effectively improve the photoactivity of TiO2, a fundamental understanding of the charge transfer process between TiO2 and MoS2 is still lacking. Herein, TiO2 photocatalysts with different exposed facets were used to construct MoS2/TiO2 heterostructures. XPS, ESR, together with PL measurements evidenced the Type II electron transfer from MoS2 to {001}-TiO2. Differently, electron-rich characteristic of {101}-faceted TiO2 were beneficial for the direct Z-scheme recombination of electrons in TiO2 with holes in MoS2. This synergetic effect between facet engineering and oxygen vacancies resulted in more than one order of magnitude enhanced hydrogen evolution rate. This finding revealed the elevating mechanism of constructing high-performance MoS2/TiO2 heterojunction based on facet and defect engineering.

Silver-nanoparticles-loaded chitosan foam as a flexible SERS substrate for active collecting analytes from both solid surface and solution.

Here, we report a dual-use surface-enhanced Raman scattering (SERS) substrate based on a flexible three-dimensional (3D) chitosan foam, onto which silver nanoparticles (Ag NPs) are firmly immobilized through amino groups from chitosan chains. The SERS substrate can actively collect analytes either on solid surface by swabbing or in solution by adsorption. The compressible characteristic of chitosan foam enables easy removal of solvent through gentle pressing, which can achieve fast pre-concentrating of analytes before measurements. In addition, the substrate is shape adaptable and thus is suitable for sampling contaminants on solid surfaces. The SERS substrates exhibit acceptable reproducibility (16.4% in relative standard deviation). Furthermore, it detects Raman probe Nile Blue A down to 5 pg by swabbing solid surface and Rhodamine 6G down to 10 ppb by adsorbing analyte in the solution. Three pesticide samples (triazophos, methidathion, and isocarbophos) can also be detected down to µg level with the substrate. It is believed that such a versatile SERS substrate may find great opportunity in realistic sensing applications.

Au@Co2P core/shell nanoparticles as a nano-electrocatalyst for enhancing the oxygen evolution reaction.

Core/shell nanoparticles (NPs) of Au@Co2P, each comprising a Au core with a Co2P shell, were prepared, and shown to efficiently catalyze the oxygen evolution reaction (OER). In particular, Au@Co2P has a small overpotential of 321 mV at 10 mA cm-2 in 1 M KOH aqueous solution at room temperature, which is about 95 mV less than pure Co2P. More importantly, the Tafel slope of Au@Co2P, at 57 mV dec-1, is 44 mV dec-1 lower than that of Co2P. Hence, Au@Co2P outperforms Co2P drastically in practical production when a high current density is required.

The electrochemical properties of Co3O4 as a lithium-ion battery electrode: a first-principles study.

Extensive first principles calculations were performed to study the structural and electrochemical features of Co3O4 during its lithiation process as an anode material for lithium-ion batteries (LIBs). We found that with up to 8 mol Li in Co3O4, the formed LinCo3O4 structures are stable for low Li concentrations of n ≤ 1, but obvious structure distortions and volume expansions occur for LinCo3O4 with n > 1. This may be the reason why Co3O4 has a high Li capability but low cycling life as a LIB anode. The ab initio molecular dynamics simulations for LinCo3O4 (n = 2, 4, 8) further suggest a two-step electrochemistry process of Co3O4 → CoO → Co upon the lithiation process. We detected a distorted surface structure as Li atoms react with the Co3O4(110) surface, which also reduces the rate capability of the Co3O4 anode.

Exploring the formation and electronic structure properties of the g-C3N4 nanoribbon with density functional theory.

The optical properties and condensation degree (structure) of polymeric g-C3N4 depend strongly on the process temperature. For polymeric g-C3N4, its structure and condensation degree depend on the structure of molecular strand(s). Here, the formation and electronic structure properties of the g-C3N4 nanoribbon are investigated by studying the polymerization and crystallinity of molecular strand(s) employing first-principle density functional theory. The calculations show that the width of the molecular strand has a significant effect on the electronic structure of polymerized and crystallized g-C3N4 nanoribbons, a conclusion which would be indirect evidence that the electronic structure depends on the structure of g-C3N4. The edge shape also has a distinct effect on the electronic structure of the crystallized g-C3N4 nanoribbon. Furthermore, the conductive band minimum and valence band maximum of the polymeric g-C3N4 nanoribbon show a strong localization, which is in good agreement with the quasi-monomer characters. In addition, molecular strands prefer to grow along the planar direction on graphene. These results provide new insight on the properties of the g-C3N4 nanoribbon and the relationship between the structure and properties of g-C3N4.

3-Fold-Periodic Size-Dependence in Electronic Properties of Monolayer-TMDC Nanotriangles.

Stable nanotriangles of monolayer transitional metal dichalcogenides (referred herein as MS2 mNTs) grown via ordinary deposition conditions, where M = Mo or W, exhibit a peculiar 3-fold periodic size-dependence in electronic and chemical properties. For " k" being the number of M atoms per edge, mNTs are (a) intrinsic-semiconducting when k = 3 i + 1, such as k = 7, 10, 13, 16; (b) metallic-like with no bandgap when k = 3 i; (c) n+ semiconducting when k = 3 i - 1. Besides changes in electronic properties, the catalytic properties for hydrogen evolution reaction also switch from active for k = 3 i and 3 i - 1 to inactive for k = 3 i + 1. The peculiar periodic size-dependence roots from the chemistry of edge-reconstruction and the consequential evolution of band structure. Further, such chemistry and thereby the size-dependence can be manipulated by adding or depleting the atomic concentration of sulfur atoms along the mNT edges.

Enhanced optical absorption via cation doping hybrid lead iodine perovskites.

The suitable band structure is vital for perovskite solar cells, which greatly affect the high photoelectric conversion efficiency. Cation substitution is an effective approach to tune the electric structure, carrier concentration, and optical absorption of hybrid lead iodine perovskites. In this work, the electronic structures and optical properties of cation (Bi, Sn, and TI) doped tetragonal formamidinium lead iodine CH(NH2)2PbI3 (FAPbI3) are studied by first-principles calculations. For comparison, the cation-doped tetragonal methylammonium lead iodine CH3NH3PbI3 (MAPbI3) are also considered. The calculated formation energies reveal that the Sn atom is easier to dope in the tetragonal MAPbI3/FAPbI3 structure due to the small formation energy of about 0.3 eV. Besides, the band gap of Sn-doped MAPbI3/FAPbI3 is 1.30/1.40 eV, which is considerably smaller than the un-doped tetragonal MAPbI3/FAPbI3. More importantly, compare with the un-doped tetragonal MAPbI3/FAPbI3, the Sn-doped MAPbI3 and FAPbI3 have the larger optical absorption coefficient and theoretical maximum efficiency, especially for Sn-doped FAPbI3. The lower formation energy, suitable band gap and outstanding optical absorption of the Sn-doped FAPbI3 make it promising candidates for high-efficient perovskite cells.

Edges of graphene and carbon nanotubes with high catalytic performance for the oxygen reduction reaction.

We invented a practical and simple wet-grinding method to break conventional graphene sheets and CNTs for the production of new graphene/CNTs with adequate edge density (about 25 000 atoms per graphene-fragment of about 1 µm2 in size) and no detectable changes in intrinsic defects, extrinsic impurities, and even surface-area. Measurements using the standard cyclic voltammetry, rotating disk electrode and rotating ring-disk electrode techniques all confirm that such mildly fragmented graphene, as well as carbon-nanotubes treated similarly using this wet-grinding method, can facilitate the fast 4-electron oxygen reduction reaction (ORR) pathway. Our first-principles computational studies of the ORR on graphene, as well as the relevant known data in the literature, support an intriguing proposition that the ORR can be speeded up simply by increasing the edge-density of graphene. The adsorption of O2 involving both oxygen atoms, which causes O-O elongation, is best facilitated at the edge of graphene, facilitating a multi-step 4-electron ORR process.

Tuning band gaps and optical absorption of BiOCl through doping and strain: insight form DFT calculations.

Bismuth oxyhalides (BiOX, X = Cl, Br, and I) are a new family of promising photocatalysts. BiOCl and BiOBr possess large band gaps and weak absorption in visible light regions, which limit their applications. Although the band gap of BiOI is suitable to absorb most of the visible light, its redox capability is very weak. In this work, the doping and strain effects on the electronic structures and optical properties of BiOCl are explored using first principle calculations. The results show that doping in BiOCl, especially co-doping of Sb and I atoms, can obviously decrease the band gaps along with enhancing the optical absorption coefficients of pristine BiOCl because of the electronegativity difference between Sb/I atoms and Bi/Cl atoms. Meanwhile the band gap of BiOCl can be tuned under strain. This work offers potential strategies to enhance BiOCl absorption coefficients in the visible light region and its photocatalyst activity.

Magnetism in the p-type Monolayer II-VI semiconductors SrS and SrSe.

Using density functional theory calculations, we study the electronic and magnetic properties of the p-type monolayer II-VI semiconductors SrX (X = S,Se). The pristine SrS and SrSe monolayers are large band gap semiconductor with a very flat band in the top valence band. Upon injecting hole uniformly, ferromagnetism emerges in those system in a large range of hole density. By varying hole density, the systems also show complicated phases transition among nonmagnetic semiconductor, half metal, magnetic semiconductor, and nonmagnetic metal. Furthermore, after introducing p-type dopants in SrS and SrSe via substitutionary inserting P (or As) dopants at the S (or Se) sites, local magnetic moments are formed around the substitutional sites. The local magnetic moments are stable with the ferromagnetic order with appreciable Curie temperature. The ferromagnetism originates from the instability of the electronic states in SrS and SrSe with the large density of states at the valence band edge, which demonstrates a useful strategy for realizing the ferromagnetism in the two dimensional semiconductors.