First-principles DFT Insights into the adsorption of hydrazine on bimetallic β1-NiZn catalyst: implications for direct hydrazine fuel cells

We present a systematic first-principles density functional theory study with dispersion corrections (DFT-D3) of hydrazine adsorption on the experimentally observed (111), (110) and (100) surfaces of the binary β1-NiZn alloy. A direct comparison has been drawn between the bimetallic and monometallic Ni and Zn counterparts to understand the synergistic effect of alloy formation. The hydrazine adsorption mechanism has been characterised through adsorption energies, Bader charges, the d-band centre model, and the coordination number of the active site - which is found to dictate the strength of the adsorbate-surface interaction. The bimetallic β1-NiZn nanocatalyst is found to exhibit higher activity towards adsorption and activation of hydrazine compared to the monometallic Ni and Zn counterparts. The Ni-sites of the bimetallic NiZn surfaces are found to be generally more reactive than Zn sites, which is suggested to be due to the higher d-band centre of -0.13 eV (closer to the Fermi level), forming higher energy anti-bonding states through Ni-N interactions. The observed synergistic effects derived from surface composition and electronic structure modification from Ni and Zn alloying should provide new possibilities for the rational design and development of low-cost bimetallic Ni-Zn alloy catalysts for direct hydrazine fuel cell (DHFC) applications

Enhanced field emission properties of Au/SnSe nano-heterostructure: a combined experimental and theoretical investigation

We report the field emission properties of two-dimensional SnSe nanosheets (NSs) and Au/SnSe nano-heterostructure (NHS) prepared by a simple and economical route of one-pot colloidal and sputtering technique. Field Emission Scanning Electron Microscope (FESEM) analysis reveal surface protrusions and morphology modification of the SnSe NSs by Au deposition. By decorating the SnSe NSs with Au nanoparticles, significant improvement in field emission characteristics were observed. A significant reduction in the turn-on field from 2.25 V/µm for the SnSe NSs to 1.25 V/µm for the Au/SnSe NHS was observed. Emission current density of 300 µA/cm2 has been achieved at an applied field of 4.00 and 1.91 V/µm for SnSe NSs and Au/SnSe NHS, respectively. Analysis of the emission current as a function of time also demonstrated the robustness of the present Au/SnSe NHS. Consistent with the experimental data, our complementary first-principles DFT calculations predict lower work function for the Au/SnSe NHS compared to the SnSe NSs as the primary origin for improved field emission. The present study has evidently provided a rational heterostructure strategy for improving various field emission related applications via surface and electronic modifications of the nanostructures

Theoretical Insights into the hydrogen evolution reaction on the Ni3N electrocatalyst

Ni-based catalysts are attractive alternatives to noble metal electrocatalysts for the hydrogen evolution reaction (HER). Herein, we present a dispersion-corrected density functional theory (DFT-D3) insight into HER activity on the (111), (110), (001), and (100) surfaces of metallic nickel nitride (Ni3N). A combination of water and hydrogen adsorption was used to model the electrode interactions within the water splitting cell. Surface energies were used to characterise the stabilities of the Ni3N surfaces, along with adsorption energies to determine preferable sites for adsorbate interactions. The surface stability order was found to be (111) < (100) < (001) < (110), with calculated surface energies of 2.10, 2.27, 2.37, and 2.38 Jm−2, respectively. Water adsorption was found to be exothermic at all surfaces, and most favourable on the (111) surface, with Eads = −0.79 eV, followed closely by the (100), (110), and (001) surfaces at −0.66, −0.65, and −0.56 eV, respectively. The water splitting reaction was investigated at each surface to determine the rate determining Volmer step and the activation energies (Ea) for alkaline HER, which has thus far not been studied in detail for Ni3N. The Ea values for water splitting on the Ni3N surfaces were predicted in the order (001) < (111) < (110) < (100), which were 0.17, 0.73, 1.11, and 1.60 eV, respectively, overall showing the (001) surface to be most active for the Volmer step of water dissociation. Active hydrogen adsorption sites are also presented for acidic HER, evaluated through the ΔGH descriptor. The (110) surface was shown to have an extremely active Ni–N bridging site with ΔGH = −0.05 eV

Enhanced photocatalytic activity of N, P, co-doped carbon quantum dots: an insight from experimental and computational approach

Herein, we demonstrate the single-step microwave radiation assisted approach to develop Nitrogen (N) and Phosphorous (P) co-doped carbon quantum dots (NP-CQD). The developed NP-CQD showed enhancement in visible light photocatalytic activity towards methylene blue dye degradation than that of N-CQD and P-CQD due to creation of energy states and reduced work function as estimated by Ultraviolet photoelectron spectroscopy and corroborated by first-principles Density Functional Theory (DFT) calculations

Structural and optical properties of ionic liquid based hybrid perovskitoid: a combined experimental and theoretical investigation

Herein, we report a novel layered lead bromide, (CH3CH2)3N+Br−(CH2)2NH+3)PbBr3, where bulky organic cations, (CH3CH2)3N+Br−(CH2)2NH+3), amino-ethyl triethyl ammonium [aetriea] were not only incorporated between the inorganic layers but also sandwiched within the inorganic [PbBr6]4− octahedral layered structure. The UV-Visible, photoluminescence spectroscopy (PL), X-ray diffraction (XRD) and a field-emission scanning electron microscope (FE-SEM) result show that the new perovskitoid has a microrod shape with an estimated bandgap of ∼3.05 eV. The structural and optoelectronic properties of the [aetriea]PbBr3perovskitoid were further corroborated by first-principles density functional theory (DFT) calculations. Thermogravimetric analysis (TGA) data show good stability of the [aetriea]PbBr3perovskitoid. Time-resolved photoluminescence (TRPL) decays from new [aetriea]PbBr3perovskitoid showing 6 ns average lifetime. These results suggest that doubly charged cation hybrid perovskite materials are potential candidates for optoelectronic applications

ZnO/CuSCN nano-heterostructure as a highly efficient field emitter: a combined experimental and theoretical investigation

We report the synthesis of two-dimensional porous ZnO nanosheets, CuSCN nanocoins, and ZnO/CuSCN nano-heterostructure thin films grown on fluorine-doped tin oxide substrates via two simple and low-cost solution chemical routes, i.e., chemical bath deposition and successive ionic layer adsorption and reaction methods. Detail characterizations regarding the structural, optoelectronic, and morphological properties have been carried out, which reveal high-quality and crystalline synthesized materials. Field emission (FE) investigations performed at room temperature with a base pressure of 1 × 10–8 mbar demonstrate superior FE performance of the ZnO/CuSCN nano-heterostructure compared to the isolated porous ZnO nanosheets and CuSCN nanocoins. For instance, the turn-on field required to draw a current density of 10 μA/cm2 is found to be 2.2, 1.1, and 0.7 V/μm for the ZnO, CuSCN, and ZnO/CuSCN nano-heterostructure, respectively. The observed significant improvement in the FE characteristics (ultralow turn-on field of 0.7 V/μm for an emission current density of 10 μA/cm2 and the achieved high current density of 2.2 mA/cm2 at a relatively low applied electric field of 1.8 V/μm) for the ZnO/CuSCN nano-heterostructure is superior to the isolated porous ZnO nanosheets, CuSCN nanocoins, and other reported semiconducting nano-heterostructures. Complementary first-principles density functional theory calculations predict a lower work function for the ZnO/CuSCN nano-heterostructure (4.58 eV), compared to the isolated ZnO (5.24 eV) and CuSCN (4.91 eV), validating the superior FE characteristics of the ZnO/CuSCN nano-heterostructure. The ZnO/CuSCN nanocomposite could provide a promising class of FE cathodes, flat panel displays, microwave tubes, and electron sources

DFT and experimental investigations on the photocatalytic activities of NiO nanobelts for removal of organic pollutants

NiO nanobelts synthesized using the hydrothermal method are explored for photocatalytic degradation of organic pollutants like RhB, MO, MB, and CV. The XPS analysis confirmed the formation of the stoichiometric NiO nanobelts. Few micrometer long cubic crystalline NiO nanobelts of the average thickness of ∼75 nm delivered a bandgap of 4.07 eV. The FTIR studies revealed that the mesoporous NiO nanobelts delivered stable photocatalytic activities after controlled irradiation under a xenon lamp. The kinetic studies showed the 79.1, 82.7, 76.7, and 89% degradation of MO, MB, CV, and RhB after 140 min at the rate constants (k) of 0.007, 0.008, 0.009, and 0.012 min−1, respectively. Complementary first-principles Density Functional Theory (DFT) and scavenging studies revealed the chemical picture and influence of the , and photogenerated from NiO nanobelts in the photocatalytic degradation of organic dyes. These studies corroborate the use of the NiO nanobelts in the stable and eco-friendly photocatalytic degradation activities of a wide range of organic pollutants

Optical, structural and morphological study of CdS nanoparticles: Role of sulphur source

Cadmium sulfide (CdS) nanoparticles were synthesized by simple and low cost homemade hot injection method at low process temperature using different sulphur sources. The effects of sulphur concentration on the structural, morphological, and optoelectronic properties of synthesized CdS films were studied using a range of characterization techniques: X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM) and UV-Visible spectroscopy. The XRD studies revealed the formation of hexagonal type CdS nanoparticles. The varying morphology dependence on the sulphur source was ascertained from FESEM analysis. The longitudinal optical (LO) phonon vibrational modes of CdS were assigned in Raman spectra at 300 and 600 cm−1. The band gap of the CdS particles was estimated to be 2.30 eV from Tauc’s plots. Consistent with the experimental results, our first-principles DFT calculations predict the band gap of CdS nanoparticles to increase with decreasing S concentration: Cd52S52 (2.38 eV) Cd52S51 (2.52 eV) and Cd52S50 (2.65 eV), with both the valence and conduction band edges demonstrated to be dominated by S-p states

Polymer-wrapped reduced graphene oxide/nickel cobalt ferrite nanocomposites as tertiary hybrid supercapacitors: insights from experiment and simulation

The tertiary hybrid supercapacitor consisting of PEDOT:PSS wrapped reduced graphene oxide/Ni0.5Co0.5Fe2O4 (PGNC) was developed and its supercapacitance performance has been compared with that of the reduced graphene oxide (rGO)/Ni0.5Co0.5Fe2O4 (GNC), carbon nanotube (CNT)/Ni0.5Co0.5Fe2O4 (CNC) and carbon nanotube/reduced graphene oxide/Ni0.5Co0.5Fe2O4 (CGNC). Among all, PGNC exhibits an excellent specific capacitance of 1286 Fg−1 with a capacitance retention of 95% over 6000 cycles at a current density of 0.5 Ag−1. The synergetic effects between rGO, Ni0.5Co0.5Fe2O4 and the PEDOT:PSS polymer result in an increase in the specific surface area and the pore volume, making PGNC an excellent hybrid supercapacitor for energy storage. The enhancement in the specific capacitance of the PGNC nanocomposite is further validated through first-principles density functional theory calculations, which predict an increment in the density of states at the Fermi level of the GNC and CNC nanocomposites compared to the isolated Ni0.5Co0.5Fe2O4 material. The supercapacitance performance of the PGNC nanocomposite is reported for different electrolytes, different stoichiometric ratios of Ni and Co in NixCo1-xFe2O4 and on different substrates

Highly active methanol oxidation electrocatalyst based on 2D NiO porous nanosheets:a combined computational and experimental study

Two-dimensional (2D) nanostructures are attractive candidates for electrocatalytic applications owing to their excellent mechanical flexibility and large exposed surfaces. In this work, we present ultra-thin 2D NiO porous nanosheets prepared by a simple, economical and green experimental method (hydrothermal, freeze-drying, and sintering) as efficient electrocatalysts for direct methanol fuel cell (DMFC) application. Benefiting from the ultra-thin 2D framework and porous nanostructure, the 550-NiO catalyst (annealed at 550 °C) exhibit higher current density (12.54mA cm−2) and faster charge transfer in the catalytic process, due to its abundant solid state redox couples (Ni2+/Ni3+= 0.991), suitable oxygen defects and surface coverage of redox species (2.90 × 10−7mol cm−2). First-principles density functional theory calculations were employed to provide mechanistic insights into the methanol oxidation reaction over the NiO catalyst via methanol dehydrogenation to CO involving O–H and C–H bond scissions, and subsequently, CHO oxidation with OH. The most plausible reaction pathway of methanol oxidation on NiO (100) is predicted to be CH3OH → CH3O → CH2O → CHO → CHOOH → COOH → CO2. The reported facile, simple, low-cost and method provides an avenue for the rational design and synthesis of 2D NiO porous nanostructured electrode materials for DMFC and beyond