NiO System Research Articles

Optimum Band Gap Energy of ((Ag),Cu)(InGa)Se2 Materials for Combination with NiMo–NiO Catalysts for Thermally Integrated Solar-Driven Water Splitting Applications

Solar-driven water splitting is considered one of the promising future routes to generate fuel in a sustainable way. A carbon-free solar fuel, molecular hydrogen, can here be produced along two different but intimately related routes, photoelectrochemical (PEC) water splitting or photovoltaic electrolysis (PV-electrolysis), where the latter builds on well-established solar cell and electrolysis materials with high efficiency. The PV-electrolysis approach is also possible to construct from an integrated PEC/PV-system avoiding dc–dc converters and enabling heat exchange between the PV and electrolyzer part, to a conventionally wired PV-electrolysis system. In either case, the operating voltage at a certain current needs to be matched with the catalyst system in the electrolysis part. Here, we investigate ((Ag),Cu)(In,Ga)Se2 ((A)CIGS)-materials with varying Ga-content modules for combination with NiMo–NiO catalysts in alkaline water splitting. The use of (A)CIGS is attractive because of the low cost-to-performance ratio and the possibility to optimize the performance of the system by tuning the band gap of (A)CIGS in contrast to Si technology. The band gap tuning is possible by changing the Ga/(Ga + In) ratio. Optoelectronic properties of the (A)CIGS materials with Ga/(Ga + In) ratios between 0.23 and 0.47 and the voltage and power output from the resulting water splitting modules are reported. Electrolysis is quantified at temperatures between 25 and 60 °C, an interval obtainable by varying the thermal heat exchange form a 1-sun illuminated PV module and an electrolyte system. The band gaps of the (A)CIGS thin films were between 1.08 to 1.25 eV and the three-cell module power conversion efficiencies (PCE) ranged from 16.44% with 1.08 eV band gap and 19.04% with 1.17 eV band gap. The highest solar-to-hydrogen (STH) efficiency was 13.33% for the (A)CIGS–NiMo–NiO system with 17.97% module efficiency and electrolysis at 60 °C compared to a STH efficiency of 12.98% at 25 °C. The increase in STH efficiency with increasing temperature was more notable for lower band gaps as these are closer to the overpotential threshold for performing efficient solar-driven catalysis, while only a modest improvement can be obtained by utilizing thermal exchange for a band gap matched PV-catalysts system. The results show that usage of cost-effective and stable thin film PV materials and earth abundant catalysts can provide STH efficiencies beyond 13% even with PV modules with modest efficiency.

Composition-dependent hardness and Young’s modulus in fcc Ni–X (X = Rh, Ta, W, Re, Os, and Ir) alloys: Experimental measurements and CALPHAD modeling

Abstract

Синтез и физико-химическое исследование нанокерамики в системе La2O3 – Mn2O3 – NiO для катодных электродов топливных элементов

Синтез и физико-химическое исследование нанокерамики в системе La2O3 – Mn2O3 – NiO для катодных электродов топливных элементов

A Computational Study on the Variation of Bandgap Due to Native Defects in Non-Stoichiometric NiO and Pd, Pt Doping in Stoichiometric NiO

This paper presents a computational study of non-stoichiometric nickel oxide in a 64-cell NiO system to model and validate localized heating effects due to nanosecond laser irradiation. Variation in the Bandgap of NiO is studied as a function of varying concentrations of native defects, ranging from 0 to 25%. It is observed that there is a slight increase in the bandgap from 3.80eV for stoichiometric NiO to 3.86eV for Ni-rich NiO and to 3.95eV for O-rich NiO. It is hence deduced that the experimental laser irradiation leads to simultaneous reduction of Ni2+ ions and the oxidation of NiO as the number of laser pulses increase. As well, a detailed study on the effects of doping nickel family elements, i.e., palladium (Pd) and platinum (Pt), in stoichiometric NiO is presented. A bandgap decrease from 3.8eV for pure NiO to 2.5eV for Pd-doping and 2.0eV for Pt-doping for varying doping concentrations ranging from 0–25% Pd, Pt, respectively,is observed.

A full potential all-electron calculation on electronic structure of NiO

We perform a first principle calculation on NiO system, a prototypical correlated electronic system due to partial filled 3d electronic shell, using various density functional theory (DFT) and hybrid functional methods inclusion of spin polarization (SP), on-site Coulomb repulsion U and spin–orbit coupling (SOC) effects. It is shown that localized spin density approximation (LSDA) plus U (LSDA + U) correctly reproduce experimental lattice parameter, while spin polarization generalized gradient approximation (SP + GGA + U) obviously overestimates lattice parameter. LSDA + U/SP + GGA + U band gaps and magnetic moments are in agreement with experimental data, and correctly predict NiO to be an insulator. NiO undergoes a Mott–Hubbard metal–insulator transition (MIT) by addition of Coulomb interaction U. Our LSDA + SOC calculation shows that SOC further splitting of Ni d eg and t2g orbitals into dz2, dxy, dx2y2 and dxz + dyz orbitals, and SP nearly cancels out SOC effect, giving rise to symmetry of density of states (DOS) for spin-up and spin-down states, hence appearance of zero net magnetic moment. For LSDA + U + SOC calculation, combination effect of SP, U and SOC results in non-occupying of spin-up conduction band and a negligible density of states for spin-down states.

Nanostructured semiconducting materials for efficient hydrogen generation

Massive production of hydrogen by water decomposition triggered by a solar light active photocatalyst is a major objective in chemistry and a promising avenue to overcome the global energy crisis. The development of efficient, stable, economically viable and eco-friendly photocatalysts for hydrogen production is a challenging task. This article reviews the use of nanocomposite in three combinations: metal oxide–metal oxide semiconductor, metal–metal oxide semiconductor and metal chalcogenide–metal oxide core–shell nanostructures. These core–shell structures occur in two forms: a simple form where the photocatalyst is either in the core or the shell or in a more complex system where the core–shell structure comprises a co-catalyst deposited on a semiconducting material. We discuss the design, synthesis and development of semiconductor-based nanocomposite photocatalysts for hydrogen production. The major points are the role of catalytic active sites, the chemical nature of sacrificial agents, the effect of light sources, the variable light intensity and the energy efficiency calculation. For TiO2-based nanocomposites, the metal oxide or metal co-catalyst loading of 1.0–3.0 wt% was optimal. TiO2 nanotube–CuO hybrid nanocomposites produce 1,14,000 µmol h−1 $${\text{g}}^{ - 1}_{\text{cat}}$$ , whereas TiO2/Au nanocomposites display 1,60,000 µmol h−1 $${\text{g}}^{ - 1}_{\text{cat}}$$ . For core–shell catalysts, a shell thickness of 2–20 nm was found for the best activity, and its performance is as follows: (a) CdS–NiO system produces around 19,949 µmol h−1 $${\text{g}}^{ - 1}_{\text{cat}}$$ and (b) CuO–Cr2O3 as co-catalyst immobilized on TiO2 system produces around 82,390 µmol h−1 $${\text{g}}^{ - 1}_{\text{cat}}$$ .

Glass-forming region and optical properties of the TeO2 – ZnO – NiO system

The glass-forming region of the ternary TeO2 – ZnO – NiO system has been determined using a conventional melt-quenching method under controlled condition. The stable samples containing up to 35mol% NiO were prepared by the rapid cooling technique while a low cooling rate was allowed to obtain glasses containing 15mol% NiO. The formation of tellurium, zinc and nickel complex oxides (e.g. NiTe2O5, Zn3Te2O8) crystalline phases in a powder batches during the glass synthesis at different temperatures were studied. Investigations of the crystallization processes in glasses showed the formation of the same complex oxides phases as in the batch. The basic thermal properties of ternary glasses were determined by DSC and an increase of glass temperature with increase in the concentration of NiO in the glass matrix was shown. The optical absorbance spectrum of the glasses exhibited three broad bands with four maxima located at about 430, 720, 810 and 1320nm corresponding to the d-d transitions of Ni2+ ion in octahedral coordination. The ligand field, splitting and Racah parameters were calculated and its dependence on the concentration of NiO was established.

Electrically insulating oxide coatings working in wide temperature range

Chemical compositions of electrically insulating coatings based on the Cr2O3–SiO2–CaO–NiO system were developed. The coatings effectively protect modern devices in a wide range of positive and negative temperatures (from –60 to +250°C).

LSDA+U study on the electronic and anti-ferromagnetic properties of Ni-doped CuO and Cu-doped NiO

Doping is an effective way to improve the activity of photocatalysts. The effect of doping on the magnetic properties of some photocatalysts that are easily recycled was studied using the local spin density approximation (LSDA)+U method on typical divalent metal oxide semiconductors CuO, NiO, Ni-doped CuO, and Cu-doped NiO. It is found that the influence of Ni doping on the spatial structure of CuO and that of Cu doping on the spatial structure of NiO are negligible because of the similar radii of Ni2+ and Cu2+. The valence band and conduction band for Ni-doped CuO are clearly spin-split, corresponding to a net effective magnetic moment of µeff = 1.66 µB. This may improve the photocatalytic efficiency and raise the recycle rate of photocatalysts. In the Cu-doped NiO system, the presence of Cu 3d states near to the Fermi level increases the width of the valence band and narrows the band gap with respect to that in pure NiO. Beyond the Cu 3d states, within the band gap, appear two energy levels around the Fermi level, which may effectively separate the electron-hole pair and also lead to enhanced absorption of visible light and infrared light. It can be concluded that the observed changes in the band structure may be helpful for improving the activity of photocatalysts and the doped systems have net magnetic moments, meaning that they are easily recycled and can be reused.

FPGA-Based HD Camera System for the Micropositioning of Biomedical Micro-Objects Using a Contactless Micro-Conveyor

With recent advancements, micro-object contactless conveyers are becoming an essential part of the biomedical sector. They help avoid any infection and damage that can occur due to external contact. In this context, a smart micro-conveyor is devised. It is a Field Programmable Gate Array (FPGA)-based system that employs a smart surface for conveyance along with an OmniVision complementary metal-oxide-semiconductor (CMOS) HD camera for micro-object position detection and tracking. A specific FPGA-based hardware design and VHSIC (Very High Speed Integrated Circuit) Hardware Description Language (VHDL) implementation are realized. It is done without employing any Nios processor or System on a Programmable Chip (SOPC) builder based Central Processing Unit (CPU) core. It keeps the system efficient in terms of resource utilization and power consumption. The micro-object positioning status is captured with an embedded FPGA-based camera driver and it is communicated to the Image Processing, Decision Making and Command (IPDC) module. The IPDC is programmed in C++ and can run on a Personal Computer (PC) or on any appropriate embedded system. The IPDC decisions are sent back to the FPGA, which pilots the smart surface accordingly. In this way, an automated closed-loop system is employed to convey the micro-object towards a desired location. The devised system architecture and implementation principle is described. Its functionality is also verified. Results have confirmed the proper functionality of the developed system, along with its outperformance compared to other solutions.

Chemical equilibrium analysis of hydrogen production from shale gas using sorption enhanced chemical looping steam reforming

Detailed chemical equilibrium analysis based on minimisation of Gibbs Energy is conducted to illustrate the benefits of integrating sorption enhancement (SE) and chemical looping (CL) together with the conventional catalytic steam reforming (C-SR) process for hydrogen production from a typical shale gas feedstock. CaO(S) was chosen as the CO2 sorbent and Ni/NiO is the oxygen transfer material (OTM) doubling as steam reforming catalyst. Up to 49% and 52% rise in H2 yield and purity respectively were achieved with SE-CLSR with a lower enthalpy change compared to C-SR at S:C 3 and 800K. A minimum energy of 159kJ was required to produce 1mol of H2 at S:C 3 and 800K in C-SR process, this significantly dropped to 34kJ/mol of produced H2 in the CaO(S)/NiO system at same operating condition without regeneration of the sorbent, when the energy of regenerating the sorbent at 1170K was included, the enthalpy rose to 92kJ/mol H2, i.e., significantly lower than the Ca-free system. The presence of inert bed materials in the reactor bed such as catalyst support or degraded CO2 sorbent introduced a very substantial heating burden to bring these materials from reforming temperature to sorbent regeneration temperature or to Ni oxidation temperature. The choice of S:C ratio in conditions of excess steam represents a compromise between the higher H2 yield and purity and lower risk of coking, balanced by the increased enthalpy cost of raising excess steam.

Structural, electronic, magnetic and optical properties of Zn1-xNixO from first-principles

The spin-polarized first-principles calculation is performed to investigate the structural, electronic, magnetic and optical properties of the Zn1-xNixO systems with x=0.00, 0.25, 0.50, 0.75, 1.00. Except for Zn0.5Ni0.5O with a tetragonal structure, the other Zn1-xNixO systems are cubic structure. Although pure ZnO is a nonmagnetic semiconductor with a band gap of 1.43eV, the Zn0.75Ni0.25O, Zn0.5Ni0.5O, Zn0.25Ni0.75O and NiO systems are completely half metal and thus usable in spintronic devices. The tetrahedral crystal field of the surrounding four O anions splits Ni-3d states into triply degenerate t2g(dxy,dyz,dzx) states with higher energy and doubly degenerate eg(dz2,dx2-y2) states with lower energy. The magnetic moments of the Zn1-xNixO systems are mainly contributed by Ni atom with the small parallel contributions of O and Zn atoms. With increasing Ni concentration, the atomic magnetic moments μ¯Ni, μ¯O, and μ¯Zn, total magnetic moment μtot, conduction band (CB) and valence band (VB) edge spin splittings ΔEC and ΔEV, spin polarized crystal field splittings ΔE↑ and ΔE↓, spin exchange splitting Δx(d), static dielectric constant ε1(0) and refractive index n(0), new appeared small absorption peak at 0–4eV increase, while the exchange constants N0α and N0β, original huge narrow absorption peak around 45eV decrease.

Oxygen Contents in Molten Ni in Equilibrium with Slag of CaO–SiO<sub>2</sub>–MgO–NiO System

A study has been carried out to measure the oxygen contents in molten Ni in equilibrium with NiO in the top slag, contained in a magnesia crucible, in the temperature range higher than 1500°C. The slag was composed of CaO–SiO2–MgO satd.-NiO system with (mass% CaO)/(mass% SiO2) = 1 and 8 mass% NiO. Firstly, it was found that oxygen content rapidly increased after adding the slag of CaO–SiO2–MgO–NiO system into molten Ni and that it took 30 minutes to attain equilibrium. The measured oxygen contents were lower than those in equilibrium with pure solid NiO and increased with an increase in temperature. Thermodynamic analysis was made on the basis of the above results. It was found that activity of NiO in the present slag of CaO–SiO2–MgO satd.-NiO system was positively deviated from ideal solution. In addition, Henry constant of NiO in this oxide system was obtained as the following relation under the assumption that Henry’s law is available:

Exchange bias effect in CoCr 2 O 4 /NiO system prepared by two-step method

Abstract CoCr 2 O 4 /NiO has been successfully synthesized through two-step method. X-ray diffraction results present the coexistence of CoCr 2 O 4 and NiO with pure formation. Micrographs measured with scanning electron microscope and transmission electron microscope display the homogeneous and dense morphology with two kinds of nanoparticles. Exchange bias effect is observed in the sample. The exchange bias field is about 872 Oe at 10 K. As measuring temperature increases, exchange bias effect is weakened with decreasing coercive field. In addition, exchange bias field and the shift of magnetization show the linear relationship with increasing cooling field. The exchange bias behavior can be attributed to the exchange coupling at the disordered interfaces in the sample.

Stability of vacancy-oxygen complexes in bulk nickel: Atomistic and ab initio calculations

This work is concerned with the interactions of multiple oxygen atoms with vacancy clusters Vm of size m in bulk nickel. The calculations were carried out using molecular statics, employing a reactive potential developed recently for the NiO system containing vacancies. In particular, segregation of oxygen inside a mono- and a divacancy are considered for the first time, to complete earlier work on the subject. Overall, we find strong attractive interactions between the oxygen atoms and the vacancy clusters. We argue that this leads to increasing dramatically the solubility of oxygen in nickel. Regarding the complexes VmO1, the results indicate that atomic oxygen inside the vacancy clusters is more stable than at the conventional interstitial sites of the perfect Ni system. This stability is further enhanced as the size of the cavity increases. We have found that a monovacancy (V1) and a divacancy (V2) can trap up to 14 and 22 oxygen atoms, respectively. We have also carried out ab initio calculations, for the purposes of both comparison and validation of the potential used in the current work. We find a very good qualitative agreement between the ab initio results and the predictions obtained from the reactive potential. Both agree well with the experimentally observed facts establishing the influence of point defects on the oxidation processes observed in nickel and its alloys.

Characterization of new compound and phase equilibria up to solidus line in the system InVO4–NiO

A new compound of the formula Ni2InVO6, belonging to the family M2AVO6 (where: M→metal(II), A→metal(III) has been obtained by the solid state reaction method. The compound was synthesized by heating in air the stoichiometric mixtures of InVO4 with NiO as well as V2O5 and In2O3 with precursor of NiO. It was characterized by powder XRD, DTA–TGA, IR, UV–Vis-DR and SEM/EDX techniques. According to the results, the new compound crystallizes in the orthorhombic system. Its unit cell parameters have been calculated. Ni2InVO6 is stable in air up to ∼1330°C. The band gap of Ni2InVO6 is ∼1.92eV as estimated from UV–Vis-DR spectrum. A phase diagram of the pseudobinary InVO4–NiO system, in which the new compound forms, up to the solidus line has been constructed.

The X-ray photoelectron spectroscopy and high-temperature structural studies of Zn1−xNixO/NiO two-phase composites

Detailed investigation of the chemical states and local atomic environment of Ni and Zn in the two-phase composites of Zn1-xNixO/NiO was reported. The X-ray photoelectron spectra of both Ni-2p and Zn-2p revealed the existence of a doublet with spin-orbit splitting approximate to 17.9 and 23.2eV, respectively confirming the divalent oxidation state of both Ni and Zn. However, the samples fabricated under oxygen-rich conditions exhibit significant difference in the binding energy approximate to 18.75eV between the 2p3/2 and 2p1/2 states of Ni. The shift in the satellite peaks of Ni-2p with increasing the Ni composition x within the Zn1-xNixO/NiO matrix signifies the attenuation of nonlocal screening because of reduced site occupancy of two adjacent Zn ions. The temperature dependence of X-ray diffraction analysis reveals a large distortion in the axial-rhombohedral angle for oxygen-rich NiO. Conversely, no significant distortion was noticed in the NiO system present as a secondary phase within Zn1-xNixO. Nevertheless, the unit-cell volume of both wurtzite h.c.p. Zn1-xNixO and f.c.c. NiO exhibits an anomalous behavior between 150 and 300 degrees C. The origin of such unusual change in the unit-cell volume was discussed in terms of oxygen stoichiometry.

Structure Property Relationship in BaTiO3–Na0.5Bi0.5TiO3–Nb2O5–NiO X8R System

A novel BaTiO3–Na0.5Bi0.5TiO3–Nb2O5–NiO (BT‐NBT‐Nb‐Ni) system that meets the X8R specification (−55°C–150°C, ΔC/C≤±15%) of multilayer ceramic capacitors (MLCCs) was fabricated, with a maximum dielectric constant of 2350 at room temperature (25°C). Core–shell microstructure was observed by transmission electron microscopy (TEM), accounting for the good dielectric temperature stability. The role of Ni on the formation of core–shell structure and phase structure, and the subsequent relationship between structure and dielectric/ionic conduction properties were investigated. It was observed that the addition of Ni could adjust the ratio of core/shell, and significantly reduces the dielectric loss over the studied temperature range. A new Ba11(Ni, Ti)28O66+x phase with a 10‐layer close‐packed structure was identified by X‐ray diffraction (XRD), serving as a source of oxygen vacancies for ionic conduction in addition to Ba(Ni,Ti)O3. Furthermore, the impedance spectroscopy measurements demonstrated the remarkable impact of these Ni‐induced oxygen vacancies on both the grain and grain‐boundary conductivities.

Spatially Confined Functionalization of Transparent NiO Thin Films with a Luminescent (1,10‐Phenanthroline)tris(2‐thenoyltrifluoroacetonato)europium Monolayer

AbstractTransparent MOCVD‐grown NiO films have been functionalized with the luminescent (1,10‐phenanthroline)tris(2‐thenoyltrifluoroacetonato)europium(III) complex [Eu(TTA)3phen] by combining sputter activation with a solution synthetic route. To introduce the Eu complex only on selected regions, some areas of the NiO surface were activated by Ar+ ion sputtering and then functionalized with 3‐phosphonopropionic acid (CPPA) followed by the anchoring of Eu(TTA)3phen through a ligand‐exchange reaction between β‐diketonato ligands and the carboxylic groups of CPPA. The functionalized material was characterized by X‐ray photoelectron, UV/Vis and luminescence spectroscopy. XPS measurements indicated that CPPA prefunctionalization and, in turn, the Eu(TTA)3phen anchoring occurs only on the sputter‐activated region, while no anchoring takes place on the unactivated surface. The optical properties of the Eu(TTA)3phen–NiO system were evaluated by UV/Vis and luminescence spectroscopy.

Mechanism study of reaction between CO and NiO(0 0 1) surface during chemical-looping combustion: Role of oxygen

First-principle calculations based on density function theory (DFT) were used to clarify the reactivity mechanism of CO with NiO(0 0 1) surface, including the effect of the oxygen species during the Ni-based oxygen carrier reduction process in chemical-looping combustion. The results indicate that the SGGA (spin-polarized generalized gradient approximation) + U (a Hubbard-type on-site Coulomb repulsion) method could give an accurate description of the reaction in the CO–NiO(0 0 1) system by comparing with experimentally determined parameters. A systematic investigation of the adsorption of CO on the NiO(0 0 1) perfect and defective surfaces was performed. It was found that CO could be only adsorbed on both surfaces, but no oxidation reactions were observed. The role of O species for the reaction between CO and NiO(0 0 1) surface was studied in detail. Our calculations clearly reveal that the oxygen vacancy exhibits a high surface reactivity toward the dissociation of O2 to O atoms and a reaction between oxygen adsorbed on the surface of NiO(0 0 1) and CO is the major reaction pathway in forming CO2.