A simple synthesis of transparent and highly conducting p-type CuxAl1−xSy nanocomposite thin films as the hole transporting layer for organic solar cells

Inorganic p-type films with high mobility are very important for opto-electronic applications. It is very difficult to synthesize p-type films with a wider, tunable band gap energy and suitable band energy levels. In this research, p-type copper aluminum sulfide (Cu_xAl_1−xS_y) films with tunable optical band gap, carrier density, hole mobility and conductivity were first synthesized using a simple, low cost and low temperature chemical bath deposition method. These in situ fabricated Cu_xAl_1−xS_y films were deposited at 60 °C using an aqueous solution of copper(ii) chloride dihydrate (CuCl₂·2H₂O), aluminium nitrate nonohydrate [Al(NO₃)₃·9H₂O], thiourea [(NH₂)₂CS], and ammonium hydroxide, with citric acid as the complexing agent. Upon varying the ratio of the precursor, the band gap of the Cu_xAl_1−xS_y films can be tuned from 2.63 eV to 4.01 eV. The highest hole mobility obtained was 1.52 cm² V⁻¹ s⁻¹ and the best conductivity obtained was 546 S cm⁻¹. The Cu_xAl_1−xS_y films were used as a hole transporting layer (HTL) in organic solar cells (OSCs), and a good performance of the OSCs was demonstrated using the Cu_xAl_1−xS_y films as the HTL. These results demonstrate the remarkable potential of Cu_xAl_1−xS_y as hole transport material for opto-electronic devices.

Inorganic p-type films with high mobility are very important for opto-electronic applications.     

Stoichiometry–grain size-specific capacitance interrelationships in nickel oxide

Nickel oxide exhibits almost the highest theoretical specific capacitance (C_s), which includes contributions from non-faradaic double layer charging and faradaic OH⁻ adsorption. However, the realistic and tangible C_s is due to the faradaic process, which can be influenced by chemical (i.e. stoichiometry) and structural (i.e. grain size) changes. Hence, it is necessary to investigate the interrelationships among chemical and structural features and charge storage capacity. Here, a non-stoichiometric nickel oxide (Ni_xO) containing Ni²⁺ and Ni³⁺ was synthesized by a sol–gel method at 620, 720 and 920 °C using Ni(NO₃)₂·6H₂O and citric acid. The grain size as estimated from X-ray diffraction increases from 55 to 194 nm with increase in the synthesis temperature. The stoichiometry measured through Ni²⁺ (or Ni³⁺) fraction from X-ray photoelectron spectroscopy also increases from 70.3 to 99.2 atom% with synthesis temperature. The C_s due to faradaic OH⁻ adsorption was estimated from cyclic voltammetry in 2 M KOH within −0.05 to +0.60 V vs. Hg/Hg₂Cl₂/KCl (sat. in water). This C_s increases from 7.5 to 92.4 F g⁻¹ with a decrease in the grain size and stoichiometry (increase in Ni³⁺) due to possibly the increased conductivity and NiOOH formation through OH⁻ adsorption. The deviation from stoichiometry at lower grain size mainly stems from nickel vacancy accommodation, according to the thermodynamic model proposed here. The interrelationships among stoichiometry, grain size and the specific capacitance of nickel oxide are investigated.

Grain size, stoichiometry and specific capacitance in NiO are interrelated.     

Comparison of NiOx thin film deposited by spin-coating or thermal evaporation for application as a hole transport layer of perovskite solar cells

We compared nickel oxide (NiO_x) deposited by thermal evaporation and that deposited by the spin-coating process, for use in the hole transport layers of inverted planar perovskite solar cells (PSCs). Spin-coating deposition for NiO_x HTL has been widely used, owing to its simplicity, low cost, and high efficiency. However, the spin-coating process has a technical limit to depositing a large-area uniformly. In contrast, thermal evaporation fabrication has a low price and is able to produce uniform and reproducible thin film. Hence, the chemical states, energy band alignment, surface morphologies, and microstructures of NiO_x deposited by spin coating and thermal evaporation were analyzed. The PSC with NiO_x HTL deposited by thermal evaporation showed a higher power conversion efficiency of 16.64% with open circuit voltage 1.07 V, short circuit current density of 20.68 mA cm⁻², and a fill factor of 75.51% compared to that of PSC with spin-coated NiO_x. We confirmed that thermal evaporation can deposit NiO_x to give a better performance as a HTL with higher reproducibility than spin-coating.

We compared nickel oxide (NiO_x) deposited by thermal evaporation and that deposited by the spin-coating process, for use in the hole transport layers of inverted planar perovskite solar cells (PSCs).     

Study on the performance of NiO/ZnxZr1−x catalysts for CO2 hydrogenation

The NiO/Zn_xZr_1−x (x represents the molar mass of Zn) catalyst was prepared by the impregnation method and tested in CO₂ methanation. The activity results show that NiO/Zn_0.3Zr_0.7 has a higher CO₂ conversion rate and methane selectivity than NiO/ZnO and NiO/ZnO–ZrO₂. Combined with N₂ adsorption–desorption, H₂-TPR, CO₂-TPD, H₂-TPD, XRD, TEM, XPS and FTIR and other characterization methods, the physical and chemical properties of NiO/ZnO–ZrO₂ were studied. The incorporation of ZnO into NiO/ZrO₂ forms a ZnO–ZrO₂ solid solution, and the combination of the solid solution weakens the interaction between NiO and the oxide support, thereby promoting the reduction and dispersion of NiO. The H₂-TPR experiment results show that, because ZnO–ZrO₂ forms a solid solution, NiO is better dispersed on the surface, resulting in a significant reduction in the reduction temperature of NiO. Using FTIR to conduct CO₂ adsorption and methanation experiments on NiO/Zn_xZr_1−x to determine the adsorbed species and intermediates, the results show that CO₂ methanation follows the formate pathway.

The NiO/Zn_xZr_1−x (x represents the molar mass of Zn) catalyst was prepared by the impregnation method and tested in CO₂ methanation.     

NiO/NixCo3−xO4 porous ultrathin nanosheet/nanowire composite structures as high-performance supercapacitor electrodes

The demand for a new generation of high-safety, long-lifespan, and high-capacity power sources increases rapidly with the growth of energy consumption in the world. Here we report a facile method for preparing architecture materials made of NiO/Ni_xCo_3−xO₄ porous nanosheets coupled with NiO/Ni_xCo_3−xO₄ porous nanowires grown in situ on nickel foams using a hydrothermal method without any binder followed by a heat treatment process. The nanosheet-shaped NiO/Ni_xCo_3−xO₄ species in the nanosheet matrix function well as a scaffold and support for the dispersion of the Ni_xCo_3−xO₄ nanowires, resulting in a relatively loose and open structure within the electrode matrix. Among all composite electrodes prepared, the one annealed in air at 300 °C displays the best electrochemical behavior, achieving a specific capacitance of 270 mF cm⁻² at 5 mA cm⁻² while maintaining excellent stability (retaining ≈ 89% of the max capacitance after 20 000 cycles), demonstrating its potential for practical application in power storage devices.

Porous ultrathin nanosheet/nanowire composite structures are prepared as high-performance supercapacitor electrodes which exhibit excellent stability.     

Facile preparation of porous sheet–sheet hierarchical nanostructure NiO/Ni–Co–Mn–Ox with enhanced specific capacity and cycling stability for high performance supercapacitors

NiO, Ni–Co–Mn–O_x and NiO/Ni–Co–Mn–O_x on nickel foam substrates were prepared via a chemical bath deposition–calcination. The thermodynamic behavior was observed by TG/DTA. The chemical structure and composition, phase structure and microstructures were tested by XPS, XRD, FE-SEM and TEM. The electrochemical performance was measured by CV, GCD and EIS. The mechanism for formation and enhancing electrochemical performance is also discussed. Firstly, the precursors such as NiOOH, CoOOH and MnOOH grow on nickel foam substrates from a homogeneous mixed solution via chemical bath deposition. Thereafter, these precursors are calcined and decomposed into NiO, Co₃O₄ and MnO₂ respectively under different temperatures in a muffle furnace. Notably, NiO/Ni–Co–Mn–O_x on nickel foam substrates reveals a high specific capacity with 1023.50 C g⁻¹ at 1 A g⁻¹ and an excellent capacitance retention with 103.94% at 5 A g⁻¹ after 3000 cycles in 2 M KOH, its outstanding electrochemical performance and cycling stability are mainly attributed to a porous sheet–sheet hierarchical nanostructure and synergistic effects of pseudo-capacitive materials and excellent redox reversibility. Therefore, this research offers a facile synthesis route to transition metal oxides for high performance supercapacitors.

NiO, Ni–Co–Mn–O_x and NiO/Ni–Co–Mn–O_x on nickel foam substrates were prepared via a chemical bath deposition–calcination.     

Structural,optical and electronic properties of Ni1−xCoxO in the complete composition range

Crystallographic and electronic structures of phase pure ternary solid solutions of Ni_1−xCo_xO (x = 0 to 1) have been studied using XRD, EXAFS and XAS measurements. The lattice parameter of the cubic rock-salt (RS) Ni_1−xCo_xO solid solutions increases linearly with increasing Co content and follows Vegard''s law, in the complete composition range. A linear increase in the bond lengths (Ni/Co–O, Ni–Ni and Ni–Co) with “x”, closely following the bond lengths determined from virtual crystal approximation (VCA), is observed, which implies that there is only a minimal local distortion of the lattice in the mixed crystal. The optical gap of the ternary solid solution determined from diffuse reflectivity measurements shows neither a linear variation with Co composition nor bowing, as observed in many ternary semiconductors. This trend in the variation of optical gaps is explained by probing the conduction band using XAS at the O K-edge. We have observed that the variation in the onset energy of the conduction band edge with “x” is very similar to the variation in the optical gap with “x”, thus clearly indicating the dominant role played by the conduction band position in determining the optical gap. The variation in the intensities of the pre-edge peak in the XANES spectra measured at Ni and Co K-edges, and the L_1/2 peak in XAS spectra measured at Ni and Co L-edges, is found to depend on the unoccupied O 2p-metal-(Ni/Co) 3d hybridized states and the bond lengths.

The optical gap of Ni_1−xCo_xO solid solutions neither varies linearly with Co composition nor shows any bowing in the complete composition range. The nature of this variation of the gap is governed by the position of conduction band edge.     

Ni2Mn-layered double oxide electrodes in organic electrolyte based supercapacitors

The development of future mobility (e.g. electric vehicles) requires supercapacitors with high voltage and high energy density. Conventional active carbon-based supercapacitors have almost reached their limit of energy density which is still far below the desired performance. Advanced materials, particularly metal hydroxides/oxides with tailored structure are promising supercapacitor electrodes to push the limit of energy density. To date, research has largely focused on evaluation of these materials in aqueous electrolyte, while this may enable high specific capacitance, it results in low working voltage window and poor cycle stability. Herein, we report the development of Ni₂Mn-layered double oxides (Ni₂Mn-LDOs) as mixed metal oxide-based supercapacitor electrodes for use in an organic electrolyte. Ni₂Mn-LDO obtained by calcination of [Ni_0.66Mn_0.33(OH)₂](CO₃)_0.175·nH₂O at 400 °C produced the best performing Ni₂Mn-LDOs with high working voltage of 2.5 V and a specific capacitance of 44 F g⁻¹ (at 1 A g⁻¹). We believe the performance of the Ni₂Mn-LDOs is related to its unique porous structure, high surface area and the homogeneous mixed metal oxide network. Ni₂Mn-LDO outperforms both the single metal oxides (NiO, MnO₂) and the equivalent physical mixture of the two oxides. We propose this performance boost arises from synergy between NiO and MnO_x due to a more effective homogeneous network of NiO/MnO_x domains in the Ni₂Mn-LDO. This work clearly shows the advantage of an LDO over the single component metal oxides as well as the physical mixture of mixed metal oxides and highlights the possibilities of development of further mixed metal oxides-based supercapacitors in organic electrolyte using LDH precursors.

Ni₂Mn-layered double oxide (LDO) electrode not only expands the working voltage and enhances the specific capacitance of layered double hydroxide (LDH) in the organic electrolyte but also outperforms NiO, MnO₂ and their physical mixture.     

The crystallization kinetics of Co doping on Ni–Mn–Sn magnetic shape memory alloy thin films

Co doping is an effective means to improve the performance of Ni–Mn–Sn alloy bulks and thin films. However, the Co doping effect on the crystallization process of the Ni–Mn–Sn alloy thin films is important but not clear. Therefore, we investigate the influence of Co doping on the crystallization kinetics for Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) magnetic shape memory alloy thin films by DSC analysis. For the non-isothermal process, each DSC curve has a single exothermic peak, which is asymmetrical. The crystallization peak temperatures and the activation energy of thin films both rise gradually with increasing Co content. Then, the activation energy of Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) thin films obtained by the Kissinger equation method is determined as 157.9 kJ mol⁻¹, 198.8 kJ mol⁻¹, 213 kJ mol⁻¹ and 253.6 kJ mol⁻¹, respectively. The local activation energy of thin films with different Co content show the different variation tendency. In the isothermal crystallization, the average of the Avrami exponent n for thin films of each Co content is approximately 1.5, suggesting that the mechanism of crystallization is two-dimensional diffusion-controlled growth for Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) thin films.

Co doping is an effective means to improve the performance of Ni–Mn–Sn alloy bulks and thin films.     

Mn-doped nickeltitanate (Ni1−xMnxTiO3) as a promising support material for PdSn electrocatalysts for methanol oxidation in alkaline media

Nickeltitanate (Ilmenite) has been prepared with stoichiometric variation by substituting Mn in the ‘A’ site, using the sol–gel method in a highly active form. The PdSn electrocatalyst was then impregnated with nickeltitanate by a microwave-assisted polyol method. The physiochemical characterisation of the synthesized electrocatalyst PdSn–Ni_1−xMn_xTiO₃ was done by X-ray diffractometry, UV-visible spectrophotometry, Raman spectroscopy and transmission electron microscopy. The elemental composition was obtained using energy dispersive spectra which confirmed the presence of Ni, Mn, Ti, O, Pd and Sn. Electrochemical characterization using cyclic voltammetry and polarization experiments showed that the synthesized PdSn–Ni_1−xMn_xTiO₃ exhibited an enhanced catalytic activity and better stability in the alkaline medium, compared to conventional PdSn/C catalysts. It was observed that the charge transfers from the support material (Ni_1−xMn_xTiO₃) to the PdSn electrocatalyst boosted the oxidation reaction. By varying the methanol concentration from 0.5 M to 2.0 M, the resulting current density also varied from 129 to 151 mA cm⁻². This result demonstrated that the prepared material PdSn–Ni_1−xMn_xTiO₃/C electrocatalyst is an excellent candidate for the methanol oxidation reaction.

Nickeltitanate (Ilmenite) has been prepared with stoichiometric variation by substituting Mn in the ‘A’ site, using the sol–gel method in a highly active form.     

Pt–Nix alloy nanoparticles: a new strategy for cocatalyst design on a CdS surface for photo-catalytic hydrogen generation

Solar photocatalytic water splitting for the production of hydrogen has been a core aspect for decades. A highly active and durable photocatalyst is crucial for the success of the renewable hydrogen economy. To date, the development of highly effective photocatalysts has been seen by the contemporary research community as a grand challenge. Thus, herein we put forward a sincere attempt to use a Pt–Ni_x alloy nanoparticle (NP) cocatalyst loaded CdS photocatalyst ((Pt–Ni_x)/CdS) for photocatalytic hydrogen production under visible light. The Pt–Ni_x alloy NP cocatalyst was synthesized using a one-pot solvothermal method. The cocatalyst nanoparticles were deposited onto the surface of CdS, forming a Pt–Ni_x/CdS photocatalyst. Photocatalytic hydrogen production was carried out using a 300 W Xe light equipped with a 420 nm cut-off filter. The H₂ evolution rate of the Pt–Ni₃/CdS photocatalyst can reach a value as high as 48.96 mmol h⁻¹ g⁻¹ catalyst, with a quantum efficiency of 44.0% at 420 nm. The experimental results indicate that this Pt–Ni₃/CdS photocatalyst is a prospective candidate for solar hydrogen generation from water-splitting.

In this report, PtNi_x alloy NPs coupled with a CdS photocatalyst for photocatalytic hydrogen generation under visible light have been explored.     

Efficient and stable perovskite solar cells using manganese-doped nickel oxide as the hole transport layer

Organic/inorganic hybrid perovskite solar cells (PSCs) have represented a promising field of renewable energy in recent years due to the compelling advantages of high efficiency, facile fabrication process and low cost. The development of inorganic p-type metal oxide materials plays an important role in the performance and stability of PSCs for commercial purposes. Herein a facile and effective way to improve hole extraction and conductivity of NiO_x films by manganese (Mn) doping is demonstrated in this study. A Mn-doped NiO_x layer was prepared by the sol–gel process and served as the hole transport layer (HTL) in inverted PSCs. The results suggest that Mn-doped NiO_x is helpful for the growth of perovskite layers with larger grains and higher crystallinity compared with the pristine NiO_x. Furthermore, the perovskite films deposited on Mn-doped NiO_x exhibit lower recombination and shorter carrier lifetime. The device based on 0.5 mol% Mn-doped NiO_x as the HTL displayed the best power conversion efficiency (PCE) of 17.35% and a high fill factor (FF) of 81%, which were significantly higher than those of the one using the pristine NiO_x HTL (PCE = 14.71%, FF = 73%). Moreover, the device retained 70% of its initial efficiency after 35 days'' storage under a continuous halogen lamp matrix exposure with an illumination intensity of 1000 W m⁻². Our results widen the development of PSCs for future production.

The device based on a Mn-doped NiO_x HTL retained 70% of its initial efficiency after 35 days’ storage under a continuous halogen lamp matrix exposure.     

The effect of stoichiometry on the structural,thermal and electronic properties of thermally decomposed nickel oxide

A thermal decomposition route with different sintering temperatures was employed to prepare non-stoichiometric nickel oxide (Ni_1−δO) from Ni(NO₃)₂·6H₂O as a precursor. The non-stoichiometry of samples was then studied chemically by iodometric titration, wherein the concentration of Ni³⁺ determined by chemical analysis, which is increasing with increasing excess of oxygen or reducing the sintering temperature from the stoichiometric NiO; it decreases as sintering temperature increases. These results were corroborated by the excess oxygen obtained from the thermo-gravimetric analysis (TGA). X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) techniques indicate the crystalline nature, Ni–O bond vibrations and cubic structural phase of Ni_1−δO. The change in oxidation state of nickel from Ni³⁺ to Ni²⁺ were seen in the X-ray photoelectron spectroscopy (XPS) analysis and found to be completely saturated in Ni²⁺ as the sintering temperature reaches 700 °C. This analysis accounts for the implication of non-stoichiometric on the magnetization data, which indicate a shift in antiferromagnetic ordering temperature (T_N) due to associated increased magnetic disorder. A sharp transition in the specific heat capacity at T_N and a shift towards lower temperature are also evidenced with respect to the non-stoichiometry of the system.

A thermal decomposition route with different sintering temperatures was employed to prepare non-stoichiometric nickel oxide (Ni_1−δO) from Ni(NO₃)₂·6H₂O as a precursor.     

Microstructure and corrosion behavior of Al95−xNixY5 (x = 7,10) glassy ribbons

In this work, we correlate the microstructure and passivation of the Al_95−xNi_xY₅ lightweight glassy ribbons (x = 7 and 10) using various techniques. The overdosed Ni (x = 10) can increase the melt viscosity and then deteriorate its glass-forming ability (GFA), ribbon formability, and Y-depleted extra layer formation. Consequently, the overdosed Ni weakens the passivation stability and corrosion resistance of the as-spun ribbon. The key role of the overdosed Ni can form a strong network and crystalline grain boundary in the amorphous matrix, which can transport Y and O to participate in the oxidation. These results can help us explore a valuable method for designing new Al-based metallic glasses.

The Al_95−xNi_xY₅ ribbon x = 7 has a Y-depleted extra film and has a longer passive zone in the polarization curve and higher corrosion resistance than x = 10.     

Design and synthesis of hierarchical NiO/Ni3V2O8 nanoplatelet arrays with enhanced lithium storage properties

Hierarchical NiO/Ni₃V₂O₈ nanoplatelet arrays (NPAs) grown on Ti foil were prepared as free-standing anodes for Li-ion batteries (LIBs) via a simple one-step hydrothermal approach followed by thermal treatment to enhance Li storage performance. Compared to the bare NiO, the fabricated NiO/Ni₃V₂O₈ NPAs exhibited significantly enhanced electrochemical performances with superior discharge capacity (1169.3 mA h g⁻¹ at 200 mA g⁻¹), excellent cycling stability (570.1 mA h g⁻¹ after 600 cycles at current density of 1000 mA g⁻¹) and remarkable rate capability (427.5 mA h g⁻¹ even at rate of 8000 mA g⁻¹). The excellent electrochemical performances of the NiO/Ni₃V₂O₈ NPAs were mainly attributed to their unique composition and hierarchical structural features, which not only could offer fast Li⁺ diffusion, high surface area and good electrolyte penetration, but also could withstand the volume change. The ex situ XRD analysis revealed that the charge/discharge mechanism of the NiO/Ni₃V₂O₈ NPAs included conversion and intercalation reaction. Such NiO/Ni₃V₂O₈ NPAs manifest great potential as anode materials for LIBs with the advantages of a facile, low-cost approach and outstanding electrochemical performances.

Hierarchical NiO/Ni₃V₂O₈ nanoplatelet arrays (NPAs) grown on Ti foil were prepared as free-standing anodes for Li-ion batteries (LIBs) via a simple one-step hydrothermal approach followed by thermal treatment to enhance Li storage performance.     

Chemical solution deposition of Y1−xGdxBa2Cu3O7−δ–BaHfO3 nanocomposite films: combined influence of nanoparticles and rare-earth mixing on growth conditions and transport properties

Y_1−xGd_xBa₂Cu₃O_7−δ–BaHfO₃ (YGBCO–BHO) nanocomposite films containing 12 mol% BHO nanoparticles and different amounts of Gd were prepared by chemical solution deposition following the trifluoroacetic route on SrTiO₃ single crystals in order to study the influence of the rare earth stoichiometry on structure, morphology and superconducting properties of these films. We optimized the growth process for each of several Gd contents of the 220 nm thick YGBCO–BHO films by varying crystallization temperature and oxygen partial pressure. This optimization process led to the conclusion that mixing the rare earths in YGBCO–BHO films leads to wider growth parameter windows compared to YBCO-BHO and GdBCO-BHO films giving larger freedom for selecting the most convenient processing parameters in order to adapt to different substrates or applications which is very important for the industrial production of coated conductors. The optimized films show a continuous increase of T_c with Gd content x from ∼90 K for the YBCO-BHO films to ∼94 K for the GdBCO-BHO films. Consequently, an increase of the 77 K self-field J_c with Gd content is observed reaching values > 7 MA cm⁻² for Gd contents x > 0.5. The transport properties of these films under applied magnetic fields are significantly improved with respect to the pristine YBCO films. All YGBCO–BHO nanocomposite films grew epitaxially with c-axis orientation and excellent out-of-plane and in-plane texture. The films are dense with a low amount of pores and only superficial indentations.

Superconducting Y_1–xGd_xBa₂Cu₃O_7–δ–BaHfO₃ nanocomposite films were prepared by chemical solution deposition on SrTiO₃ substrates in order to study the influence of the rare earth stoichiometry on their structure, morphology and electrical properties.     

Solution combustion synthesis of Ni-based hybrid metal oxides for oxygen evolution reaction in alkaline medium

Oxygen evolution reaction (OER) has arisen as an outstanding technology for energy generation, conversion, and storage. Herein, we investigated the synthesis of nickel-based hybrid metal oxides (Ni_xM_1−xO_y) and their catalytic performance towards OER. Ni_xM_1−xO_y catalysts were synthesized by solution combustion synthesis (SCS) using the metal nitrates as oxidizer and glycine as fuel. Scanning electron microscope (SEM) micrographs display a porous morphology for the hybrid binary Ni_xM_1−xO_y, the common feature of combusted materials. X-ray diffraction (XRD) of Ni_xM_1−xO_y depicted well-defined diffraction peaks, which confirms the crystalline nature of synthesized catalysts. The particle size of as-synthesized materials ranges between 20 and 30 nm with a mesoporous nature as revealed by N₂-physisorption. The electrocatalytic performance of the as-prepared materials was evaluated towards OER in alkaline medium. Among them, Ni_xCo_1−xO_y showed the best catalytic performance. For instance, it exhibited the lowest overpotential at a current density of 10 mA cm⁻² (404 mV), onset potential (1.605 V), and Tafel slope (52.7 mV dec⁻¹). The enhanced electrocatalytic performance of Ni_xCo_1−xO_y was attributed to the synergism between cobalt and nickel and the alteration of the electronic structure of nickel. Also, Ni_xCo_1−xO_y afforded the highest Ni³⁺/Ni²⁺ when compared to other electrocatalysts. This leads to higher oxidation states of Ni species, which promote and improve the electrocatalytic activity.

Ni-based mixed transition metal oxides (MTMO) (Ni_xM_1−xO_y) were synthesized using the solution combustion synthesis (SCS), and investigated as electrocatalysts towards oxygen evolution reaction (OER) in alkaline medium.     

Reactive adsorption desulfurization of NiO and Ni0 over NiO/ZnO–Al2O3–SiO2 adsorbents: role of hydrogen pretreatment

Reactive adsorption desulfurization (RADS) of Fluidized Catalytically Cracked (FCC) gasoline on reduced and unreduced NiO/ZnO–Al₂O₃–SiO₂ adsorbents was studied. Various characterizations such as powder X-ray diffraction (XRD), H₂-temperature-programmed reduction (H₂-TPR), the H₂/O₂ pulse titration (HOPT), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) are used to evaluate the effects of hydrogen pretreatment of the adsorbents. XRD and HOPT results indicate that NiO is hard to be reduced to Ni⁰ under the conditions of RADS. H₂-TPR shows that NiO might be reduced to Ni⁰ at the temperature of 598 °C, much higher than the temperature of RADS. The Ni 2p_3/2 spectrum of Ni⁰ is not observed for the reduced adsorbent, but the main peak of Ni 2p_3/2 of NiS is found for the spent adsorbent. The unreduced NiO/ZnO–Al₂O₃–SiO₂ adsorbent performs a better desulfurization than the reduced adsorbent at the beginning of desulfurization process. NiO and Ni⁰ are assumed as the main active components and present a good desulfurization ability in RADS. Finally, a change in the RADS mechanism is presented and discussed.

A possible reaction mechanism of desulfurization on NiO/ZnO–Al₂O₃–SiO₂ is discussed.     

Synthesis and enhanced visible light photocatalytic CO2 reduction of BiPO4–BiOBrxI1−x p–n heterojunctions with adjustable energy band

A series of novel BiPO₄–BiOBr_xI_1−x p–n heterojunctions were successfully prepared by a facile solvothermal method. The morphology, structure and optical properties of photocatalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and ultraviolet visible diffuse reflectance spectroscopy. The visible light photocatalytic activities of BiPO₄–BiOBr_xI_1−x heterojunctions were investigated by photocatalytically reducing CO₂. After 4 hours of irradiation, the 5% BiPO₄–BiOBr_0.75I_0.25 heterojunction showed the highest photocatalytic activity with the yields of CO and CH₄ up to 24.9 and 9.4 μmol g_cat⁻¹ respectively. The improved photocatalytic activity may be due to the formation of BiPO₄–BiOBr_xI_1−x p–n heterojunctions which can effectively restrict the recombination rate of the photoexcited charge carriers. Moreover, the energy band structure of BiPO₄–BiOBr_xI_1−x heterojunctions could be easily adjusted by changing the mole ratio of I and Br. The possible mechanism of the enhancement of the photocatalytic performance was also proposed based on experimental and theoretical analysis. The present study may provide a rational strategy to design highly efficient heterojunctions with an adjustable energy band for environmental treatment and energy conversion.

A series of novel BiPO₄–BiOBr_xI_1−x p–n heterojunctions were successfully prepared by a facile solvothermal method.     

All-vacuum deposited perovskite solar cells with glycine modified NiOx hole-transport layers

Organic–inorganic hybrid perovskite solar cells (PSCs) have attracted enormous research attention due to their high efficiency and low cost. However, most of the PSCs with high efficiencies still need expensive organic materials as their hole-transport layer (HTL). Obviously, the highly expensive materials go against the low-cost concept of advanced PSCs. In this regard, inorganic NiO_x was considered as an idea HTL due to its good transmittance in the visible region and outstanding chemical stability. But for most of the PSCs with a NiO_x HTL, the hole-extraction efficiency was limited by the unmatched valence band and too many surface defects of the NiO_x layer, especially for the vacuum-deposited NiO_x and perovskite. Herein, we developed a facile strategy to overcome this issue by using self-assembled glycine molecules to treat the NiO_x surface. With glycine on the surface, the NiO_x exhibited a deeper valence band maximum and a faster charge-extraction at the NiO_x/perovskite interface. What''s more, the vacuum-deposited perovskite showed a better crystallinity on the NiO_x + glycine substrate. As a result, the PSCs with a glycine interfacial layer achieved a champion PCE of 17.96% with negligible hysteresis. This facile approach is expected to be further developed for fabricating high-efficiency PSCs on textured silicon solar cells.

Self-assembled glycine molecules are used to modify E-beam evaporated NiO_x films. The glycine interlayer improved the crystallinity and band alignment of perovskite with NiO_x. The all vacuum-processed PSCs achieved a champion PCE of 17.96% with negligible hysteresis.