Showing papers on "Nitride published in 2017"
TL;DR: A facile synthetic strategy for nitrogen-deficient graphitic carbon nitride (g-C3 Nx) is established, involving a simple alkali-assisted thermal polymerization of urea, melamine, or thiourea, with superior visible-light photocatalytic performance compared to pristine g-C2 N4.
Abstract: A facile synthetic strategy for nitrogen-deficient graphitic carbon nitride (g-C3 Nx ) is established, involving a simple alkali-assisted thermal polymerization of urea, melamine, or thiourea. In situ introduced nitrogen vacancies significantly redshift the absorption edge of g-C3 Nx , with the defect concentration depending on the alkali to nitrogen precursor ratio. The g-C3 Nx products show superior visible-light photocatalytic performance compared to pristine g-C3 N4 .
1,535 citations
TL;DR: In this article, the degradation of delaminated-Ti3C2Tx colloidal solutions was investigated and protocols to improve their stability were proposed. But the degradation was limited to 5, 10, and 15 days.
Abstract: Two-dimensional (2D) transition metal carbides and nitrides (MXenes) have shown outstanding performances in electrochemical energy storage and many other applications. Delamination of MXene flakes in water produces colloidal solutions that are used to manufacture all kinds of products (thin films, coatings, and electrodes, etc.). However, the stability of MXene colloidal solutions, which is of critical importance to their application, remains largely unexplored. Here we report on the degradation of delaminated-Ti3C2Tx colloidal solutions (T represents the surface functionalities) and outline protocols to improve their stability. Ti3C2Tx MXene solutions in open vials degraded by 42%, 85%, and 100% after 5, 10, and 15 days, respectively, leading to the formation of cloudy-white colloidal solutionss containing primarily anatase (TiO2). On the other hand, the solution could be well-preserved when Ti3C2Tx MXene colloidal solutionss were stored in hermetic Ar-filled bottles at 5 °C, because dissolved oxygen, th...
935 citations
TL;DR: In this article, the authors discuss the building blocks of carbon nitride materials and examine how strategies in synthesis, templating and post-processing translate from the molecular level to macroscopic properties, such as optical and electronic bandgap.
Abstract: In the past decade, research in the field of artificial photosynthesis has shifted from simple, inorganic semiconductors to more abundant, polymeric materials For example, polymeric carbon nitrides have emerged as promising materials for metal-free semiconductors and metal-free photocatalysts Polymeric carbon nitride (melon) and related carbon nitride materials are desirable alternatives to industrially used catalysts because they are easily synthesized from abundant and inexpensive starting materials Furthermore, these materials are chemically benign because they do not contain heavy metal ions, thereby facilitating handling and disposal In this Review, we discuss the building blocks of carbon nitride materials and examine how strategies in synthesis, templating and post-processing translate from the molecular level to macroscopic properties, such as optical and electronic bandgap Applications of carbon nitride materials in bulk heterojunctions, laser-patterned memory devices and energy storage devices indicate that photocatalytic overall water splitting on an industrial scale may be realized in the near future and reveal a new avenue of ‘post-silicon electronics’ Carbon nitrides are potentially cheap and metal-free alternatives for catalysts, semiconductors, battery materials and memory devices In this Review, we discuss the synthesis, design and morphology of these materials, and reflect on the ability of methods such as templating, etching, dye sensitization, heteroatom doping and co-polymerization, as well as the assembly of various heterojunctions, to improve device performance
705 citations
TL;DR: Benefiting from the inherent structure of 2D crystals, the ultrathin tri-s-triazine-based CCNNSs provide a broad range of application prospects in the fields of bioimaging, and energy storage and conversion.
Abstract: Tri-s-triazine-based crystalline carbon nitride nanosheets (CCNNSs) have been successfully extracted via a conventional and cost-effective sonication-centrifugation process. These CCNNSs possess a highly defined and unambiguous structure with minimal thickness, large aspect ratios, homogeneous tri-s-triazine-based units, and high crystallinity. These tri-s-triazine-based CCNNSs show significantly enhanced photocatalytic hydrogen generation activity under visible light than g-C3 N4 , poly (triazine imide)/Li+ Cl- , and bulk tri-s-triazine-based crystalline carbon nitrides. A highly apparent quantum efficiency of 8.57% at 420 nm for hydrogen production from aqueous methanol feedstock can be achieved from tri-s-triazine-based CCNNSs, exceeding most of the reported carbon nitride nanosheets. Benefiting from the inherent structure of 2D crystals, the ultrathin tri-s-triazine-based CCNNSs provide a broad range of application prospects in the fields of bioimaging, and energy storage and conversion.
512 citations
TL;DR: The selective etching of Al from ternary layered transition metal nitride Ti2AlN (MAX) and intercalation were achieved by immersing the powder in a mixture of potassium fluoride and hydrochloric acid and centrifuged to obtain few-layered Ti2NTx.
Abstract: We report on the synthesis, characterization, and application of Ti2N (MXene), a two-dimensional transition metal nitride of M2X type. Synthesis of nitride-based MXenes (Mn+1Nn) is difficult due to their higher formation energy from Mn+1ANn and poor stability of Mn+1Nn layers in the etchant employed, typically HF. Herein, the selective etching of Al from ternary layered transition metal nitride Ti2AlN (MAX) and intercalation were achieved by immersing the powder in a mixture of potassium fluoride and hydrochloric acid. The multilayered Ti2NTx (T is the surface termination) obtained was sonicated in DMSO and centrifuged to obtain few-layered Ti2NTx. MXene formation was verified, and the material was completely characterized by Raman spectroscopy, XRD, XPS, FESEM-EDS, TEM, STM, and AFM techniques. Surface-enhanced Raman scattering (SERS) activity of the synthesized Ti2NTx was investigated by fabricating paper, silicon, and glass-based SERS substrates. A Raman enhancement factor of 1012 was demonstrated usin...
404 citations
TL;DR: The current state of understanding of carbon nitride compounds is evaluated to highlight key issues in these areas and point out new directions in their development as advanced technological materials.
Abstract: Carbon nitride compounds with high N : C ratios and graphitic to polymeric structures are being investigated as potential next-generation materials for incorporation in devices for energy conversion and storage as well as for optoelectronic and catalysis applications. The materials are built from C- and N-containing heterocycles with heptazine or triazine rings linked via sp2-bonded N atoms (N(C)3 units) or –NH– groups. The electronic, chemical and optical functionalities are determined by the nature of the local to extended structures as well as the chemical composition of the materials. Because of their typically amorphous to nanocrystalline nature and variable composition, significant challenges remain to fully assess and calibrate the structure–functionality relationships among carbon nitride materials. It is also important to devise a useful and consistent approach to naming the different classes of carbon nitride compounds that accurately describes their chemical and structural characteristics related to their functional performance. Here we evaluate the current state of understanding to highlight key issues in these areas and point out new directions in their development as advanced technological materials.
353 citations
TL;DR: A facile method based on self-assembly to produce self-supported CN aerogels, without using any cross-linking agents are developed, which shows great potential for solar-to-chemical energy conversion by artificial photosynthesis.
Abstract: Aerogel structures have attracted increasing research interest in energy storage and conversion owing to their unique structural features, and a variety of materials have been engineered into aerogels, including carbon-based materials, metal oxides, linear polymers and even metal chalcogenides. However, manufacture of aerogels from nitride-based materials, particularly the emerging light-weight carbon nitride (CN) semiconductors is rarely reported. Here, we develop a facile method based on self-assembly to produce self-supported CN aerogels, without using any cross-linking agents. The combination of large surface area, incorporated functional groups and three-dimensional (3D) network structure, endows the resulting freestanding aerogels with high photocatalytic activity for hydrogen evolution and H2 O2 production under visible light irradiation. This work presents a simple colloid chemistry strategy to construct 3D CN aerogel networks that shows great potential for solar-to-chemical energy conversion by artificial photosynthesis.
277 citations
TL;DR: In this paper, the authors reported a composite MoN@nitrogen-doped carbon (MoN-NC) nano-octahedron derived from metal-organic frameworks (MOFs).
Abstract: Developing highly efficient and affordable noble-metal-free catalysts toward the hydrogen evolution reaction (HER) is an important step toward the economical production of hydrogen. As a nonprecious-metal catalyst for the HER, molybdenum nitride (MoN) has excellent corrosion resistance and high electrical conductivity, but its catalytic activity is still inadequate. Here we report our findings in dramatically enhancing the HER activity of MoN by creating porous MoN@nitrogen-doped carbon (MoN-NC) nano-octahedrons derived from metal–organic frameworks (MOFs). The composite catalyst displays remarkably high catalytic activity, demonstrating a low overpotential of 62 mV at a current density of 10 mA cm–2 (η10), a small Tafel slope of 54 mV dec–1, and a large exchange current density of 0.778 mA cm–2 while maintaining good stability. The enhancement in catalytic properties is attributed to the unique nanostructure of the MoN, the high porosity of the electrode, and the synergistic effect between the MoN and th...
276 citations
TL;DR: High magnetic moments, high Curie temperatures, robust ferromagnetism, and intrinsic half-metallic transport behavior of M2NTx nitride MXene structures suggest that they are promising candidates for spintronic applications, which should stimulate interest in their synthesis.
Abstract: Two-dimensional materials with intrinsic and robust ferromagnetism and half-metallicity are of great interest to explore the exciting physics and applications of nanoscale spintronic devices, but no such materials have been experimentally realized In this study, we predict several M2NTx nitride MXene structures that display these characteristics based on a comprehensive study using a crystal field theory model and first-principles simulations We demonstrate intrinsic ferromagnetism in Mn2NTx with different surface terminations (T = O, OH, and F), as well as in Ti2NO2 and Cr2NO2 High magnetic moments (up to 9 μB per unit cell), high Curie temperatures (1877 to 566 K), robust ferromagnetism, and intrinsic half-metallic transport behavior of these MXenes suggest that they are promising candidates for spintronic applications, which should stimulate interest in their synthesis
262 citations
TL;DR: This study shows how gas treatment synthesis such as ammoniation can transform carbide MXenes into 2D nitrides with higher electrical conductivities and metallic behavior, opening a new avenue in 2D materials synthesis.
Abstract: MXenes are a rapidly growing class of 2D transition metal carbides and nitrides, finding applications in fields ranging from energy storage to electromagnetic interference shielding and transparent conductive coatings. However, while more than 20 carbide MXenes have already been synthesized, Ti4N3 and Ti2N are the only nitride MXenes reported so far. Here by ammoniation of Mo2CTx and V2CTx MXenes at 600 °C, we report on their transformation to 2D metal nitrides. Carbon atoms in the precursor MXenes are replaced with N atoms, resulting from the decomposition of ammonia molecules. The crystal structures of the resulting Mo2N and V2N were determined with transmission electron microscopy and X-ray pair distribution function analysis. Our results indicate that Mo2N retains the MXene structure and V2C transforms to a mixed layered structure of trigonal V2N and cubic VN. Temperature-dependent resistivity measurements of the nitrides reveal that they exhibit metallic conductivity, as opposed to semiconductor-like behavior of their parent carbides. As important, room-temperature electrical conductivity values of Mo2N and V2N are three and one order of magnitude larger than those of the Mo2CTx and V2CTx precursors, respectively. This study shows how gas treatment synthesis such as ammoniation can transform carbide MXenes into 2D nitrides with higher electrical conductivities and metallic behavior, opening a new avenue in 2D materials synthesis.
259 citations
TL;DR: This work demonstrates a general and scalable pathway to enable the high-temperature capacitive energy applications of a wide range of engineering polymers and also offers an efficient method for the synthesis and transfer of 2D nanomaterials at the scale demanded for applications.
Abstract: Polymer dielectrics are the preferred materials of choice for power electronics and pulsed power applications. However, their relatively low operating temperatures significantly limit their uses in harsh-environment energy storage devices, e.g., automobile and aerospace power systems. Herein, hexagonal boron nitride (h-BN) films are prepared from chemical vapor deposition (CVD) and readily transferred onto polyetherimide (PEI) films. Greatly improved performance in terms of discharged energy density and charge-discharge efficiency is achieved in the PEI sandwiched with CVD-grown h-BN films at elevated temperatures when compared to neat PEI films and other high-temperature polymer and nanocomposite dielectrics. Notably, the h-BN-coated PEI films are capable of operating with >90% charge-discharge efficiencies and delivering high energy densities, i.e., 1.2 J cm-3 , even at a temperature close to the glass transition temperature of polymer (i.e., 217 °C) where pristine PEI almost fails. Outstanding cyclability and dielectric stability over a straight 55 000 charge-discharge cycles are demonstrated in the h-BN-coated PEI at high temperatures. The work demonstrates a general and scalable pathway to enable the high-temperature capacitive energy applications of a wide range of engineering polymers and also offers an efficient method for the synthesis and transfer of 2D nanomaterials at the scale demanded for applications.
TL;DR: In this paper, the primary amine groups on the heptazine-based polymer melon, also known as graphitic carbon nitride (g-C3N4), can be replaced by urea groups using a two-step postsynthetic functionalization.
Abstract: The primary amine groups on the heptazine-based polymer melon, also known as graphitic carbon nitride (g-C3N4), can be replaced by urea groups using a two-step postsynthetic functionalization. Under simulated sunlight and optimum Pt loading, this urea-functionalized carbon nitride has one of the highest activities among organic and polymeric photocatalysts for hydrogen evolution with methanol as sacrificial donor, reaching an apparent quantum efficiency of 18% and nearly 30 times the hydrogen evolution rate compared to the nonfunctionalized counterpart. In the absence of Pt, the urea-derivatized material evolves hydrogen at a rate over four times that of the nonfunctionalized one. Since “defects” are conventionally accepted to be the active sites in graphitic carbon nitride for photocatalysis, the work here is a demonstrated example of “defect engineering,” where the catalytically relevant defect is inserted rationally for improving the intrinsic, rather than extrinsic, photocatalytic performance. Furthermore, the work provides a retrodictive explanation for the general observation that g-C3N4 prepared from urea performs better than those prepared from dicyandiamide and melamine. In-depth analyses of the spent photocatalysts and computational modeling suggest that inserting the urea group causes a metal-support interaction with the Pt cocatalyst, thus facilitating interfacial charge transfer to the hydrogen evolving centers.
TL;DR: In this paper, a variety of techniques were applied to discuss systematic effect on the morphology, optical, electronic properties and structure of GQDs/mpg-C 3 N 4 composites.
Abstract: Hydroxyl-graphene quantum dots (GQDs) modified mesoporous graphitic carbon nitride (mpg-C 3 N 4 ) composites were fabricated through electrostatic interactions. A variety of techniques were applied to discuss systematic effect on the morphology, optical, electronic properties and structure of GQDs/mpg-C 3 N 4 composites. Remarkably, the 0.5 wt% GQDs/mpg-C 3 N 4 composites exhibited higher photocatalytic activity than that of the pure mpg-C 3 N 4 by using rhodamine B (RhB) and colorless tetracycline hydrochloride (TC) as pollutants under visible light irradiation. The results indicated that uniform dispersion of GQDs on the surface of mpg-C 3 N 4 and intimate contact between the two materials contributed to the enhanced activity. Radical trapping experiments and electron spin resonance tests both certified that the GQDs/mpg-C 3 N 4 composites can generate more O 2 − species and a small fraction of holes for photocatalytic degradation.
TL;DR: In this paper, a mesoporous nickel-iron nitride (Ni3FeN) was synthesized by thermal ammonalysis of hierarchal NiFe layered double hydroxide microspheres.
TL;DR: This work demonstrates the first molecular-level conversion pathway of NO oxidation over a novel SrO-clusters@amorphous carbon nitride (SCO-ACN) photocatalyst, which is synthesized via copyrolysis of urea and SrCO3, and presents a novel in situ DRIFTS-based strategy to explore the photocatalytic reaction pathway.
Abstract: This work demonstrates the first molecular-level conversion pathway of NO oxidation over a novel SrO-clusters@amorphous carbon nitride (SCO-ACN) photocatalyst, which is synthesized via copyrolysis of urea and SrCO3. The inclusion of SrCO3 is crucial in the formation of the amorphous carbon nitride (ACN) and SrO clusters by attacking the intralayer hydrogen bonds at the edge sites of graphitic carbon nitride (CN). The amorphous nature of ACN can promote the transportation, migration, and transformation of charge carriers on SCO-ACN. And the SrO clusters are identified as the newly formed active centers to facilitate the activation of NO via the formation of Sr-NOδ(+), which essentially promotes the conversion of NO to the final products. The combined effects of the amorphous structure and SrO clusters impart outstanding photocatalytic NO removal efficiency to the SCO-ACN under visible-light irradiation. To reveal the photocatalytic mechanism, the adsorption and photocatalytic oxidation of NO over CN and SC...
TL;DR: Wang et al. as discussed by the authors reported a ficile solvothermal method to synthesize controllable O-doped graphitic carbon nitride (g-C3N4) catalysts at low temperature.
Abstract: Tailoring defective conjugated heterocyclic network to make for broaden light absorption and efficient charge separation for photocatalytic application is an urgent assignment for graphitic carbon nitride (g-C3N4) materials. Here we report a ficile “one-pot” solvothermal method to synthesize controllable O-doped g-C3N4 catalysts at low temperature. By this template-free approach, hollow microsphere O-doped g-C3N4 products were obtained. Structure characterization reveals that the as-prepared sample has incomplete heptazine heterocyclic ring structure, and appears O doping in the lattice, which may derived from the activated O2 molecular. With the extending condensation time, the increased heteroelement doping content and narrowed band gap promote the light harvesting and charge separation efficiency. Compared to pristine g-C3N4 prepared under high-temperature calcination, this novel material show remarkably photocatalytic activity for environment pollutant purification and splitting water for H2 evolution, even though the conduction level decrease. This work highlights that the architecture and electronic properties of g-C3N4 based materials could be facile control through mild solvothermal route, which is a reference way for design and fabricate highly efficient non-metal photocatalyst with peculiar feature.
TL;DR: In this article, a facile method was developed to fabricate bimetallic Ni-Mo nitride nanotubes, which can serve as highly active and stable bifunctional electrocatalysts for full water splitting.
Abstract: Designing low-cost, highly active and stable electrocatalysts is very important to various renewable energy storage and conversion devices Herein we develop a facile method to fabricate bimetallic Ni–Mo nitride nanotubes, which can serve as highly active and stable bifunctional electrocatalysts for full water splitting To drive a current density of 10 mA cm−2, the bimetallic Ni–Mo nitride nanotubes require an overpotential of 295 mV for the OER and 89 mV for the HER The alkaline water electrolyzer with the nanotubes as cathode and anode catalysts requires a cell voltage of ca 1596 V to achieve a current density of 10 mA cm−2 Furthermore, the nanotubes for full water splitting show excellent stability even at a high current density of 370 mA cm−2, superior to the integrated performance of commercial Pt and IrO2 Our experimental results show that the NiOOH and NH groups formed at the catalyst surface during the OER process are active species for the OER, while the Ni(OH)2, NH and Mo species at the catalyst surface play a key role in the HER The present strategy may open an avenue for fabrication of low-cost, highly active and stable electrocatalysts for large-scale water splitting
TL;DR: In this paper, a cobalt-doped graphitic carbon nitride (Co CN) was synthesized by one-step thermal polycondensation using cobalt phthalocyanine (CoPc) and melamine as precursors.
TL;DR: The present work provides an efficient approach to prepare a 3 D interconnected porous nickel-cobalt nitride network with exposed inner active sites for overall water splitting that shows good stability and superior catalytic performance toward both HER and OER with low overpotentials.
Abstract: Exploring highly efficient and durable bifunctional electrocatalysts from earth-abundant low-cost transition metals is central to obtaining clean hydrogen energy through large-scale electrolytic water splitting. Porous nickel–cobalt nitride nanosheets on macroporous Ni foam (NF) are synthesized through facile electrodeposition followed by a one-step annealing process in a NH3 atmosphere. The transformation from a metal hydroxide into a metal nitride could efficiently enhance the electrocatalytic performance for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Interestingly, the incorporation of nickel further boosts the catalytic activity of cobalt nitride. When used as bifunctional electrocatalysts, the obtained nickel–cobalt nitride electrocatalyst shows good stability and superior catalytic performance toward both HER and OER with low overpotentials of 0.29 and 0.18 V, respectively, to achieve a current density of 10 mA cm−2. The good electrocatalytic performance was also evidenced by the fabrication of an electrolyzer for overall water splitting, which exhibits a high gas generation rate for hydrogen and oxygen with excellent stability during prolonged alkaline water electrolysis. The present work provides an efficient approach to prepare a 3 D interconnected porous nickel–cobalt nitride network with exposed inner active sites for overall water splitting.
TL;DR: TA spectroscopy reveals an electron-transfer cascade that correlates with a near-doubling in photocatalytic activity from 2050 to 3810 μmol h-1 g-1 when the authors infuse a suspension of bulk g-C3N4 with 10% mass loading of chemically exfoliated carbon nitride.
Abstract: Solar hydrogen generation from water represents a compelling component of a future sustainable energy portfolio. Recently, chemically robust heptazine-based polymers known as graphitic carbon nitrides (g-C3N4) have emerged as promising photocatalysts for hydrogen evolution using visible light while withstanding harsh chemical environments. However, since g-C3N4 electron-transfer dynamics are poorly understood, rational design rules for improving activity remain unclear. Here, we use visible and near-infrared femtosecond transient absorption (TA) spectroscopy to reveal an electron-transfer cascade that correlates with a near-doubling in photocatalytic activity from 2050 to 3810 μmol h–1 g–1 when we infuse a suspension of bulk g-C3N4 with 10% mass loading of chemically exfoliated carbon nitride. TA spectroscopy indicates that exfoliated carbon nitride quenches photogenerated electrons on g-C3N4 at rates approaching the molecular diffusion limit. The TA signal for photogenerated electrons on g-C3N4 decays wi...
TL;DR: It is discovered that nitride anion chemistry exhibits unique stability against Li metal, which is either thermodynamically intrinsic or a result of stable passivation.
Abstract: Lithium metal battery is a promising candidate for high-energy-density energy storage. Unfortunately, the strongly reducing nature of lithium metal has been an outstanding challenge causing poor stability and low coulombic efficiency in lithium batteries. For decades, there are significant research efforts to stabilize lithium metal anode. However, such efforts are greatly impeded by the lack of knowledge about lithium-stable materials chemistry. So far, only a few materials are known to be stable against Li metal. To resolve this outstanding challenge, lithium-stable materials have been uncovered out of chemistry across the periodic table using first-principles calculations based on large materials database. It is found that most oxides, sulfides, and halides, commonly studied as protection materials, are reduced by lithium metal due to the reduction of metal cations. It is discovered that nitride anion chemistry exhibits unique stability against Li metal, which is either thermodynamically intrinsic or a result of stable passivation. The results here establish essential guidelines for selecting, designing, and discovering materials for lithium metal protection, and propose multiple novel strategies of using nitride materials and high nitrogen doping to form stable solid-electrolyte-interphase for lithium metal anode, paving the way for high-energy rechargeable lithium batteries.
TL;DR: High-gain optical parametric amplification is experimentally demonstrated using USRN, which is compositionally tailored such that the 1,550 nm wavelength resides above the two-photon absorption edge, while still possessing large nonlinearities.
Abstract: CMOS platforms operating at the telecommunications wavelength either reside within the highly dissipative two-photon regime in silicon-based optical devices, or possess small nonlinearities. Bandgap engineering of non-stoichiometric silicon nitride using state-of-the-art fabrication techniques has led to our development of USRN (ultra-silicon-rich nitride) in the form of Si7N3, that possesses a high Kerr nonlinearity (2.8 × 10−13 cm2 W−1), an order of magnitude larger than that in stoichiometric silicon nitride. Here we experimentally demonstrate high-gain optical parametric amplification using USRN, which is compositionally tailored such that the 1,550 nm wavelength resides above the two-photon absorption edge, while still possessing large nonlinearities. Optical parametric gain of 42.5 dB, as well as cascaded four-wave mixing with gain down to the third idler is observed and attributed to the high photon efficiency achieved through operating above the two-photon absorption edge, representing one of the largest optical parametric gains to date on a CMOS platform. Typical CMOS materials in the telecommunications band suffer from two-photon absorption or possess weak Kerr nonlinearities. Here, Ooiet al. demonstrate 42.5 dB optical parametric amplification in ultra-silicon-rich nitride waveguides, designed to have strong nonlinearities with negligible losses.
TL;DR: In this paper, the authors obtained the aqueous titanium carbonitride (Ti3CNTx) colloidal solution in the absence of hydrofluoric acid or organic solvents' intercalation processes and suppressed the notorious nanosheets restacking issue through a freeze-drying strategy of the colloidal dispersion.
TL;DR: In this article, a computational study of molybdenum nitride (MoN2) nanosheet as a catalyst for ammonia synthesis at room temperature under the scheme of density functional theory is presented.
Abstract: Metallic two-dimensional materials are emerging as promising catalysts for several reactions. This work reports a computational study of molybdenum nitride (MoN2) nanosheet as a catalyst for ammonia synthesis at room temperature under the scheme of density functional theory. Pure MoN2 shows excellent performance for dinitrogen adsorption and activation, but large energy input is needed to refresh the surface following the reaction. Iron (Fe) doping can effectively improve it to achieve full nitrogen reduction with a calculated overpotential of 0.47 V, indicating that Fe-doped MoN2 is a promising catalyst for electrochemical synthesis of ammonia from water and air.
TL;DR: This study describes a metallic Ni-Fe nitride/nitrogen-doped graphene hybrid in which 2D Ni- Fe nitride nanoplates are strongly coupled with the graphene support and results in very high OER activity with the lowest onset overpotential reported, and good ORR activity comparable to that for commercial Pt/C.
Abstract: Obtaining bifunctional electrocatalysts with high activity for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is a main hurdle in the application of rechargeable metal-air batteries Earth-abundant 3d transition metal-based catalysts have been developed for the OER and ORR; however, most of these are based on oxides, whose insulating nature strongly restricts their catalytic performance This study describes a metallic Ni-Fe nitride/nitrogen-doped graphene hybrid in which 2D Ni-Fe nitride nanoplates are strongly coupled with the graphene support Electronic structure of the Ni-Fe nitride is changed by hybridizing with the nitrogen-doped graphene The unique heterostructure of this hybrid catalyst results in very high OER activity with the lowest onset overpotential (150 mV) reported, and good ORR activity comparable to that for commercial Pt/C The high activity and durability of this bifunctional catalyst are also confirmed in rechargeable zinc-air batteries that are stable for 180 cycles with an overall overpotential of only 077 V at 10 mA-2
TL;DR: In this paper, the microstructure and tribological properties of the nitrided layer and as-cast high-entropy alloy were studied at dry sliding condition, deionized water and acid rain, respectively.
TL;DR: In this paper, S nanodots are impregnated with microporous carbon and encapsulated with conductive mesoporous vanadium nitride nanowires (S/MVN@C NWs) as high performance S cathode materials for Li-S batteries.
TL;DR: In this paper, carbon nitride with different microstructural features, such as degree of polymerization, hydrogen bonds, bandgap, structural defects and ratio of C/N, were synthesized by polymerization of different types of nitrogen-rich precursors.
Abstract: Carbon nitride has emerged as one of the most attractive materials for developing photocatalysts with low cost, high efficiency and structural stability. However, fast charge recombination caused intrinsically by the π–π conjugated electronic system severely limits its photocatalytic performance. Constructing carbon nitride photocatalysts with modulated electronic structures is thus a promising but challenging task. In this paper, carbon nitride with different microstructural features, such as degree of polymerization, hydrogen bonds, bandgap, structural defects and ratio of C/N, were synthesized by polymerization of different types of nitrogen-rich precursors. Synergetic reactions were rationally designed for hydrogen production and the efficient and simultaneous removal of multiple contaminants, using carbon nitrides as metal-free photocatalysts. The significant impact of hydrogen bonds on synergetic photocatalysis was comprehensively demonstrated. With the smallest amount of hydrogen bonds, carbon nitride derived from urea exhibited fast charge transfer between interlayers, which is a prerequisite for superior photoactivity. By contrast, the polymerization of melamine and cyanamide was favorable for the formation of abundant hydrogen bonds and intrinsic vacancy defects. It was found that the coexistence of nitrogen deficiency and oxygen-doped microstructures could facilitate the activation of oxygen molecules, and thereby contributed to their moderate photoactivity. This research provides fundamental insights into the microstructural engineering of carbon nitride for high-performance synergetic applications.
TL;DR: Different from conventional methods, a facile preparation of conductive carbon nitride from novel thermal decomposition of nickel hydrogencyanamide in a confined space is reported.
Abstract: Conductive carbon nitride, as a hypothetical carbon material demonstrating high nitrogen doping, high electrical conductivity, and high surface area, has not been fabricated. A major challenge towards its fabrication is that high conductivity requires high temperature synthesis, but the high temperature eliminates nitrogen from carbon. Different from conventional methods, a facile preparation of conductive carbon nitride from novel thermal decomposition of nickel hydrogencyanamide in a confined space is reported. New developed nickel hydrogencyanamide is a unique precursor which provides self-grown fragments of ⋅NCN⋅ or NCCN and conductive carbon (C-sp2) catalyst of Ni metal during the decomposition. The final product is a tubular structure of rich mesoporous and microporous few-layer carbon with extraordinarily high N doping level (≈15 at%) and high extent of sp2 carbon (≈65%) favoring a high conductivity (>2 S cm−1); the ultrahigh contents of nongraphitic nitrogen, redox active pyridinic N (9 at%), and pyrrolic N (5 at%), are stabilized by forming NiN bonds. The conductive carbon nitride harvests a large capacitance of 372 F g−1 with >90% initial capacitance after 10 000 cycles as a supercapacitor electrode, far exceeding the activated carbon electrodes that have <250 F g−1.
TL;DR: In this paper, it was shown that the more acidic precursors, such as commercially available 5-aminotetrazole, upon pyrolysis in LiCl/KCl salt melt yield Potassium poly(heptazine imide) (PHI) with the greatly improved structural order and thermodynamic stability.
Abstract: Potassium poly(heptazine imide) (PHI) is a photocatalytically active carbon nitride material that was recently prepared from substituted 1,2,4-triazoles Here we show that the more acidic precursors, such as commercially available 5-aminotetrazole, upon pyrolysis in LiCl/KCl salt melt yield PHI with the greatly improved structural order and thermodynamic stability Tetrazole-derived PHIs feature long range crystallinities and unconventionally small layer-stacking distances leading to the altered electronic band structures as shown by Mott-Schottky analyses Under the optimized synthesis conditions, visible light driven hydrogen evolution rates reach twice the rate provided by the previous golden standard, mesoporous graphitic carbon nitride having much higher surface area More interestingly, the up to 07 V higher valence band potential of crystalline PHI compared to the ordinary carbon nitrides makes it an efficient water oxidation photocatalyst which works even in the absence of any metal-based co-catalysts under visible light To our knowledge, this is the first case of a metal free oxygen liberation from water as such