Defective NiO Research Articles

Hierarchical crystalline/defective NiO nanoarrays with (111) crystal orientation for effective electrochromic energy storage

Developing high performance electrochromic materials with energy storage function is essential for next generation smart display devices. Here, a double-layer NiO film (NiO-dl) was prepared by compositing the defective NiO (d-NiO) with the crystalline NiO (c-NiO), with a unique prismatic nanosheet array structure. The synergistic effect as well as the large active area with defect sites and valence modulation brought about by the (111) crystal plane-oriented growth of the sputtering process can promote the intercalation and extraction of OH− and Li+, which greatly enhances the electrochemical properties. Specifically, the NiO-dl film achieves a prominent optical modulation covering visible region (89.5 % in KOH and 64.8 % in Li+ electrolyte at 550 nm) and near-infrared region (54.5 % in KOH and 37.2 % in Li+ electrolyte at 1000 nm), a high transparent bleached state (92.7 %), a superior coloring efficiency (44.7 cm2 C−1) and robust stability (95.1 % retention after 1000 cycles). A high area capacitance of 99.5 mF cm−2 at 0.14 mA cm−2 with the promising cycling performance exhibits the supercapacitor characteristics. The comprehensive evaluation of the NiO-dl film demonstrated its exploitative potential application in electrochromic energy storage fields.

Sulfate anchored on the defective NiO by ion irradiation realizes enhanced oxygen evolution reaction

NiO has attracted wide attention in the past decade as a cost-effective electrochemical catalyst for OER. However, its relatively poor performance and conductivity limit its commercial applications. Here, we highlight a unique ion irradiation method to enhance the catalytic activity of NiO. Benefiting from sulfate anchoring and the introduction of oxygen vacancies by He+ ion irradiation, the optimal catalyst (ir-S-NiO) exhibits an outstanding OER performance with a low overpotential of 269 mV at 10 mA cm−2. Moreover, the fabricated Anion exchange membrane water electrolyzer (AEMWE) constructed by the ir-S-NiO is demonstrated to need a cell voltage of 1.72 V to reach a current density of 0.1 A cm−2 and shows remarkably long-term stability for 200 h without obvious attenuation at the current density of 0.5 A cm−2. This work provides a new method for the development of high-performance and stable OER electrocatalysts.

Efficient photothermal catalytic CO2 reduction over in situ construction ZnIn2S4@Ni(OH)2/NiO Z-scheme heterojunction

Photocatalytic reduction of CO2 into valuable chemicals has been considered as a sustainable and environmentally friendly technology, which can simultaneously alleviate the energy crisis and environmental problems that have puzzled people for a long time. Herein, we successfully synthesize defective ZnIn2S4@Ni(OH)2/NiO (ZIS@NOH/NiO) Z-scheme heterojunction photocatalysts through solvothermal and low-temperature calcination strategies. The loading of Ni(OH)2 nanosheets can increase the specific surface area of photocatalyst, and form Z-scheme heterojunction with ZIS to improve the utilization of photogenerated electrons. It is worth noting that during the low-temperature calcination process, Ni(OH)2 is partially converted into NiO, and a large number of metal defects are formed, which reduces the bandgap of Ni(OH)2 and shows visible light response. In addition, the generated black defective NiO with full spectrum response and good photothermal effects can accelerate the migration of photogenerated carriers and reduce the catalytic reaction barrier of CO2. Consequently, the prepared ZIS@NOH/NiO exhibits a high yield (133.74 μmol g−1) and selectivity (86.2 %) for CO2 to CH4, which almost is 3.2 and 11.1 times than those of ZnIn2S4@Ni(OH)2 and ZnIn2S4, respectively. Furthermore, in-situ Fourier transform infrared spectroscopy (FTIR) analysis reveal the effective adsorption of CO2 on the ZnIn2S4@Ni(OH)2/NiO surface and the high selectivity of CH4. This work will provide meaningful prospects for designing a carbon dioxide reduction photocatalyst with high conversion and selective.

Modification of the Ni-NiO-oxidant system by thermo-chemical oxidation with accelerated growth of the p-type dielectric oxide layer, by the action of substituted V2O5 on the system

Nickel is covered with very thin oxide film and is stable against corrosion under normal conditions. Nickel, as Ni-NiO-oxidant system, can make much thicker (even a thousand times) and more corrosion unstable oxides. With certain new oxidation process parameters, nickel can undergo so-called accelerated oxidation. The subject and goal of this work is to find the most favorable conditions for performing of accelerated - catastrophic Ni oxidation process, when substitution of V2O5 is carried out into NiO (2V (Ni)), with significant electron concentration increase and oxygen surplus. Unlimited main and secondary charge carriers transfer is significantly facilitated if oxide film with non-stoichiometric composition and defects is formed. The aim is to avoid compact oxide film formation by chemical-thermal treatments and to obtain porous and defective NiO. By using oxidized system Ni - NiO - oxidant in glass, ceramics and evaporated metal technology, extraordinary usable value of this work is ensured.

Defective NiO as a Stabilizer for Au Single-Atom Catalysts

Defective NiO as a Stabilizer for Au Single-Atom Catalysts

Insights into Syngas Combustion on a Defective NiO Surface for Chemical Looping Combustion: Oxygen Migration and Vacancy Effects

A thorough theoretical analysis of vacancy effects on syngas combustion was conducted for the chemical looping combustion (CLC) process using NiO as an oxygen carrier (OC). A density functional the...

Facile preparation and characterization of NiO/Ni2O3-decorated nanoballs and mixed phase CdS nano rods (CdS&NiO/Ni2O3) for effective photocatalytic decomposition of Congo red under visible light irradiation

This study reports the preparation of a new CdS&NiO/Ni2O3 photocatalyst having efficient and stable photocatalytic performance. The aim was to block the photocorrosion of CdS with maintaining photocatalytic activity. The prepared CdS and NiO/Ni2O3 particles were in the form of nanorods and nanoballs, respectively. Diffuse reflectance spectra (DRS), X-ray diffraction (XRD), ultraviolet-visible light (UV–vis), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Raman analysis, electrochemical impedance and photoluminescence analysis were performed to evaluate structural, morphological and optical properties and their effect on photocatalytic activity. CdS&NiO/Ni2O3 catalysts absorbed visible light and enhanced charge separation than that of CdS and NiO/Ni2O3. The catalytic performance of the samples was tested on Congo red. The optimal content of CdS&NiO/Ni2O3 was observed in CN3 sample. XPS results of defective NiO with different oxygen species showed powerful photocatalytic activities. These prepared photocatalysts need to be explored further in the decomposition of various environmental pollutants.

Effect of hot-casted NiO hole transport layer on the performance of perovskite solar cells

NiO is extensively studied as a hole transport layer in perovskite solar cells but syntheses of NiO precursor involves toxic chemicals and time-consuming processes. Moreover, the synthesized NiO contains surface defects acting as trapping sites at the NiO/perovskite interfaces, resulting in poor charge extraction, hysteresis and light soaking. In this manuscript, we developed a non-toxic methodology for NiO precursor solution by using a simple mixture of NiO powder and HCl in an air environment. In addition, a new hot-casting technique was developed to successfully fabricate densely-packed, less defective NiO films. Interestingly, the hot-casting temperature was found to significantly affect morphology, film coverage and surface defects of NiO films. When a hot-casting temperature was below 100 °C, non-uniform NiO films were sparsely formed on the FTO surface and were characterized by defects in the form of hydroxyl groups and water on the surface. Such defective NiO films resulted in severe hysteresis and light soaking effect due to the trapped charges at the defective NiO/perovskite interface of perovskite solar cells. In contrast, when the hot-casting temperature was 120 °C, the NiO film formed densely-packed morphologies, covering the FTO surface. Furthermore, this film exhibited an ordered chemistry with strong Ni-O octahedral bonding and facilitated charge extraction at NiO/perovskite interface, resulting in a negligible hysteresis and light soaking. Finally, this non-toxic and simple method of fabricating NiO film will assist further development of perovskite solar cells.

Electronic properties of doped and defective NiO: A quantum Monte Carlo study

NiO is a canonical Mott (or charge-transfer) insulator and, as such, is notoriously difficult to describe using density functional theory (DFT)--based electronic structure methods. Doped Mott insulators such as NiO are of interest for various applications but rigorous theoretical descriptions are lacking. Here, we use quantum Monte Carlo methods, which very accurately include electron-electron interactions, to examine energetics, charge structures, and spin structures of NiO with various point defects, such as vacancies and substitutional doping with potassium. The formation energy of a potassium dopant is significantly lower than that of a Ni vacancy, making potassium an attractive monovalent dopant for NiO. We compare our results with DFT results that include an on-site Hubbard $U$ ($\mathrm{DFT}\phantom{\rule{0.28em}{0ex}}+\phantom{\rule{0.28em}{0ex}}U$) to account for correlations and find relatively large discrepancies for defect formation energies as well as for charge and spin redistributions in the presence of point defects. Beyond fitting to a single property, it is unlikely that single-parameter tuning of the $\mathrm{DFT}\phantom{\rule{0.28em}{0ex}}+\phantom{\rule{0.28em}{0ex}}U$ will be able to obtain accurate accounts of complex properties in these materials. Responses that depend in subtle and complex ways on ground-state properties, such as charge and spin densities, are likely to contain quantitative and qualitative errors.

Adsorption properties of transition metal atoms on strongly correlated NiO(001) surfaces with surface oxygen vacancies

Using first-principles density functional theory combined with on-site Coulomb repulsion U, we have systematically studied the adsorption properties of transition metal (TM) atoms on strongly correlated NiO(001) surfaces with Fs centers (surface O vacancies). For the TM atoms, the adsorption on Fs centers is 1.26–3.18 eV more stable compared to positions near the surface O sites of defect-free NiO(001) surfaces. This indicates that Fs centers play an important role in the binding of TM atoms on O-defective NiO(001) surfaces. An analysis of the electronic structures and the charge redistribution for the adsorption of TM atoms on defective NiO(001) has been performed. The TM atoms are negatively charged, with charges ranging from −0.29 to −0.73 |e|. The TM-related states caused by interactions between TMs and surface defect states are found in the gap region of NiO. These results provide important information about controlling and understanding the adsorption properties of TM atoms on metal-supported ultrathin NiO films with surface defects like Fs centers.

Study of the growth of ultrathin films of NiO on Cu(111)

We have studied the early stages of growth of the layers formed by Ni evaporation in an oxygen atmosphere at room temperature on a Cu(111) single crystal. The layers have been analysed by XPS and x-ray absorption spectroscopy as a function of the deposition time. A background analysis of the XPS spectra has also been performed. We have found a Stranski-Krastanov way of growth, i.e. the formation of a metallic Ni monolayer followed by the formation of defective NiO islands. Further deposition leads to the formation of stoichiometric NiO.

Surface Defect Characterization in Oxygen-Dosed Nickel Surfaces and in NiO Thin Films by CO Adsorption−Desorption Experiments

Oxygen-covered Ni(110) as well as thin NiO films grown by oxidation of that surface were characterized under ultrahigh vacuum by using low-energy electron diffraction (LEED), X-ray photoelectron (XPS), Auger (AES), and ion scattering (ISS) spectroscopies together with CO temperature-programmed desorption (TPD) titrations. Results from NiO(100) films with surface defects induced via Ar+ ion irradiation at room temperature were compared with those from partially oxidized ordered Ni(110) surfaces. CO TPD proved to be a useful local probe for the investigation of defective NiO surfaces, since its adsorption energy varies by over 20 kcal/mol in going from a metallic Ni(110) clean surface to NiO. The CO-probing experiments also revealed that Ar+ bombardment of thin NiO films leads to the formation of Ni−O phases similar to those found during the early oxidation stages of the Ni metal surface.

Thermal annealing of defects in highly defective NiO nanoparticles studied by X-ray and electron spectroscopies

We studied the electronic structure of highly defective NiO nanoparticles using X-ray and electron spectroscopies. The spectra of NiO nanoparticles exhibit splittings which are not present in the spectra of bulk NiO. These extra splittings are attributed to changes in the crystal field caused by both adsorbates and defects. Thermal annealing of the nanoparticles reduces the splittings observed in the spectra. The changes observed in the spectra up to 300°C are attributed mostly to the desorption of various adsorbates. The changes observed above 300°C are attributed to the annealing out of defects. The spectra annealed at higher temperatures approach the spectra of bulk NiO. We suggest that the defects are unsaturated NiO bonds at the surface of the nanoparticles.

Reaction of SO2 with stoichiometric and defective NiO(100) surfaces.

The interaction of ${\mathrm{SO}}_{2}$ with both stoichiometric and defective NiO(100) surfaces has been studied by x-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, Auger-electron spectroscopy, and low-energy electron diffraction. Surface defects are found to play an important role in chemisorption. ${\mathrm{SO}}_{2}$ interacts only weakly with the stoichiometric NiO(100) surface at room temperature. The adsorption that does occur yields adsorbates having direct S-O bonds (i.e., the S 2p core-level binding energy is 167 eV); the species is presumably associatively adsorbed ${\mathrm{SO}}_{2}$. Subsequent heating of the ${\mathrm{SO}}_{2}$-exposed surface to 570 K results in desorption of the adsorbate without any changes in the S 2p binding energy. In contrast, the interaction of ${\mathrm{SO}}_{2}$ with the defective, reduced NiO(100) surface is much stronger. At 111 K only associatively adsorbed ${\mathrm{SO}}_{2}$ is present. Upon heating to about 260 K, in addition to the original adsorbates with direct S-O bonds, adsorbates having a S 2p binding energy of 162 eV are observed; these correspond to sulfide bonds to surface metal cations, which indicates that some of the ${\mathrm{SO}}_{2}$ has completely dissociated. By comparing the results from stoichiometric and defective NiO(100) surfaces, active adsorption sites that involve oxygen vacancies and steps are suggested as an explanation for the dissociation at room temperature, and a thermally activated dissociation mechanism is proposed that involves adsorption at oxygen-vacancy sites only.

Surface photovoltage and XPS studies of electronic structure in defective nickel oxide powders

Surface photovoltage measurements of polycrystalline powder samples of nickel oxide have revealed differences in band bending ( V s) related to the defect concentrations of the oxide. The powders prepared at 700°C and 1450°C in air consist of small single crystals with low concentrations ( <10 9 cm −2) of extended defects, but considerably different nickel vacancy concentrations. The defective NiO (700°C) gave V s = 760 mV and the equilibrated NiO (1450°C) V s = 230 mV under UV illumination, possibly due to Fermi level pinning of the Ni 3d 8 band near V′ Ni and V″ Ni, respectively. These results are consistent with values of V s (i.e. 630 and 240 mV, respectively) for these two samples obtained previously from XPS measurements of the dependence of surface charging on temperature. A visible transition at ≈ 2.5 eV, giving Δφ = 135 mV, is also found in the equilibrated NiO (1450°C) sample but not in the defective NiO (700°C) sample. The results are discussed in relation to other work on the electronic band structure and surface states of nickel oxide.

Surface photovoltage and XPS studies of electronic structure in defective nickel oxide powders

Surface photovoltage measurements of polycrystalline powder samples of nickel oxide have revealed differences in band bending ( V s) related to the defect concentrations of the oxide. The powders prepared at 700°C and 1450°C in air consist of small single crystals with low concentrations (<10 9 cm -2) of extended defects, but considerably different nickel vacancy concentrations. The defective NiO (700°C,) gave V s =760 mV and the equilibrated NiO (1450°C) V s =230 mV under UV illumination, possibly due to Fermi level pinning of the Ni 3d 8 band near V′ Ni and V″ Ni, respectively. These results are consistent with values of V s (i.e. 630 and 240 mV, respectively) for these two samples obtained previously from XPS measurements of the dependence of surface charging on temperature. A visible transition at ≈2.5 eV, giving Δ∮=135 mV, is also found in the equilibrated NiO (1450°C) sample but not in the defective NiO (700°C) sample. The results are discussed in relation to other work on the electronic band structure and surface states of nickel oxide.

Studies of the thermal decomposition of βNiO(OH) and nickel peroxide by X-ray photoelectron spectroscopy

The thermal decomposition of both βNiO(OH) and ‘nickel peroxide’ have been studied by combining X-ray photoelectron spectroscopic (X.p.s.) studies of the solid with mass-spectrometric analysis of the gas phase. Through monitoring the O(1s) and Ni(2p) spectra of the as-prepared solids during decomposition, with simultaneous analysis of the gas phase, it has been established that ‘nickel peroxide’ behaves in an identical fashion to βNiO(OH). We conclude that the two solids are chemically identical; on the other hand previous studies of ‘nickel peroxide’ have suggested it to be a hydrated defective oxide Ni2O3. Central to our argument is the observation that both solids exhibit initially a single O(1s) peak at 530.5 eV, but during decomposition this peak splits into two components, one at 529.7 eV and the other at 531.4 eV. It is suggested that intercalated water within the βNiO(OH) structure results in the equivalence (by X.p.s.) of the ‘oxygen species’ through the stabilisation of ‘OHO’ groups. Water and molecular oxygen are the predominant gaseous decomposition products, the solid, at 773 K, being converted into defective NiO.