Nanoporous Nickel Oxide Research Articles

Controlled Synthesis of Nanoporous Nickel Oxide with Two‐Dimensional Shapes through Thermal Decomposition of Metal–Cyanide Hybrid Coordination Polymers

AbstractInvited for the cover of this issue is the group of Yusuke Yamauchi at the National Institute for Materials Science (NIMS), Japan. The image depicts the formation of metal–cyanide hybrid coordination polymers—the rate of formation is slow as the reactant appears to be fairly stable, leading to a preferential growth. Read the full text of the article at 10.1002/chem.201404895.

Electrochemical Characterization of Nanoporous Nickel Oxide Thin Films Spray-Deposited onto Indium-Doped Tin Oxide for Solar Conversion Scopes

Nonstoichiometric nickel oxide (NiOx) has been deposited as thin film utilizing indium-doped tin oxide as transparent and electrically conductive substrate. Spray deposition of a suspension ofNiOxnanoparticles in alcoholic medium allowed the preparation of uniformNiOxcoatings. Sintering of the coatings was conducted at temperatures below 500°C for few minutes. This scalable procedure allowed the attainment ofNiOxfilms with mesoporous morphology and reticulated structure. The electrochemical characterization showed thatNiOxelectrodes possess large surface area (about 1000 times larger than their geometrical area). Due to the openness of theNiOxmorphology, the underlying conductive substrate can be contacted by the electrolyte and undergo redox processes within the potential range in whichNiOxis electroactive. This requires careful control of the conditions of polarization in order to prevent the simultaneous occurrence of reduction/oxidation processes in both components of the multilayered electrode. The combination of the open structure with optical transparency and elevated electroactivity in organic electrolytes motivated us to analyze the potential of the spray-depositedNiOxfilms as semiconducting cathodes of dye-sensitized solar cells of p-type when erythrosine B was the sensitizer.

Layer-by-layer motif hybridization: nanoporous nickel oxide flakes wrapped into graphene oxide sheets toward enhanced oxygen reduction reaction.

Herein we report a novel strategy involving the hybridization of nanoporous NiO flakes with graphene oxide (GO) sheets. The as-prepared flake-like nickel cyano-bridged coordination polymers (NiCNNi) are hybridized with GO sheets and thermally treated in air, so the organic materials can be removed without affecting the integrity of the parent GO sheets. Thus, the layer-by-layer construction followed by a thermal treatment can produce a new hybrid nanoporous material consisting of NiO and GO. The obtained hybrid material exhibits an efficient catalytic activity and stability for the oxygen reduction reaction (ORR).

Efficient Elimination of Lithium Carbonate/Carboxylates By NiO for Rechargeable Li–O2 Battery

The non-aqueous lithium–oxygen (Li–O2) battery has been extensively investigated by virtue of its remarkably high theoretical energy density. However, the Li–O2 cell has suffered from parasitic side reactions due to superoxide (O2 •−) attack and lithium peroxide (Li2O2) activity to non-aqueous electrolytes and carbon cathodes, which form lithium carbonates (Li2CO3) and carboxylates (RCO2Li, R = H or alkyl). These poor-conducting side products deposited on the cathode increase the recharge potential, which triggers the parasitic side reactions further. Some efforts to employ superoxide-tolerant electrolytes, carbon-free cathodes and cycling with limited depth of discharge have alleviated the side reactions whereas the lithium carbonates/carboxylates inevitably formed are overwhelmingly deposited on the cathode for cycling thus terminating the Li–O2 cell operation rapidly. Here, we present new approach to promote elimination of lithium carbonate/carboxylates using nanoporous nickel oxide (NiO), which enhances cycling performance and round trip efficiency of Li–O2 battery for cycling. The crystalline nanoporous NiO plates that were homogeneously distributed on the entangled carbon nanotubes (CNT) network via hydrothermal synthesis (NiO/CNT) exhibit striking capacity retention of over 70 cycles at a limited discharge capacity of 1000 mAh gCNT −1 with a stable recharge potential of 4.1 V vs. Li/Li+ in tetraglyme electrolyte. The role of nanoporous NiO is investigated under the cycling at deep depth of discharge. Unlike the first cycle providing predominant Li2O2, the increasing extent of lithium carbonates/carboxylates for cycling are observed by 1H NMR and FTIR spectroscopies. In particular, the lithium carbonates become a main side product over 10 cycles. Interestingly, the NiO/CNT cathodes reveal disappearance of these side products after every recharge and high capacity retention, which are different from NiO-free CNT cathodes providing the accumulated side products and swift capacity fading. Further analysis using anodic potential sweeps of side products in three-electrode cell demonstrate ~300 mV lower oxidation potential on the NiO/CNT than the NiO-free CNT while negligible influence on the electrolyte oxidation, which implies a promoter of nanoporous NiO to eliminate lithium carbonates/carboxylates. TEM images display that the side products seem to transport along the CNT and make a lump close to the NiO, where the decomposition of side products can be carried out actively. The nanoporous NiO has been very stable during deep cycling, where either chemical or structural change is not observed, which indicates that the NiO can contribute toward stable long-term cycling performance of Li–O2 cell.

Fabrication of nanoporous nickel oxide by de-zincification of Zn–Ni/(TiO2-nanotubes) for use in electrochemical supercapacitors

NiO–ZnO/TiO2NTs electrodes were synthesized by the electrodeposition of Zn–Ni onto TiO2 nanotubes, dealloying in a concentrated alkaline solution and finally calcination of the resulting Zn(OH)2–Ni(OH)2/TiO2NTs at 300°C. Morphology of the electrodeposited nanostructures was studied using scanning electron microscopy (SEM) while their electrochemical characterizations were carried out using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge procedures. The SEM analysis revealed the nanoporous/cracked structures of the NiO–ZnO/TiO2NTs obtained at the electroplating time of 20min. The EIS studies showed that nanoporous/cracked structures of prepared electrodes can significantly improve the parameters effectively influencing the capacitive behavior such as ohmic resistance (Rs), charge transfer resistance (Rct) and constant phase element (CPE). The electrochemical investigations showed that the specific capacitance of these electrodes were around 130mFcm−2 (325Fg−1) in 1.0M NaOH electrolyte as measured at a current density of 0.45mAcm−2 (1.1Ag−1). The modified electrodes also showed high stability and maintained 92% of initial capacity in 1.0M NaOH electrolyte after ten days of being used in electrochemical experiments.

Dendritic nanoporous nickel oxides for a supercapacitor prepared by a galvanic displacement reaction with chlorine ions as an accelerator

Dendritic nanoporous nickel oxide and tube-like nickel–tin oxide electrodes were prepared by a galvanic displacement reaction in an aqueous electrolyte containing chlorine ions which dramatically accelerated the reaction. The nanoporous nickel oxide showed a capacitance of 1242 F g−1, 97.4% of which was retained even after 5000 charge–discharge cycles.

Formation of nanoporous nickel oxides for supercapacitors prepared by electrodeposition with hydrogen evolution reaction and electrochemical dealloying

Highly nanoporous nickel oxide electrodes were obtained by electrodeposition accompanied by hydrogen evolution reaction and the selective electrochemical dealloying of copper from Ni-(Cu) porous foam. The nanoporous nickel oxide electrodes consequently have numerous dendritic morphologies composed of nanopores with 20–30 nm diameters. The specific capacitances were 428 F g−1 for as-deposited Ni-(Cu) foam electrode and 1,305 F g−1 for nanoporous nickel-oxide electrode after dealloying process, respectively. This indicates increased surface area by dealloying process leads to innovative increase of specific capacitance.

Nanoporous nickel oxide thin films and its improved electrochromic performance: Effect of thickness

Electrochromic properties of chemically bath deposited nanoporous NiO thin films were investigated as a function of film thickness using Ni sulphate precursor, aqueous ammonia and potassium persulphate as complexing and oxidizing agents respectively. The films were characterized for their structural, morphological, optical and electrochromic properties using X-ray diffraction, scanning electron microscopy, FT-IR spectroscopy, cyclic voltammetry, chronoamperometry and optical transmittance studies. X-ray diffraction patterns show that the films are polycrystalline, consisting of NiO cubic phase. Infrared spectroscopy results show the presence of free hydroxyl ion and water in NiO thin films. SEM micrographs revealed nanoporous nature composed of interconnected nanoporous network, forming well defined 3D nano envelopes. The optical band gap energy was found to be decreased from 3.22 to 2.80eV with increasing film thickness. The electrochromic properties of all the films were investigated in aqueous (KOH) and non aqueous (LiClO4-PC) electrolyte by means of cyclic voltammetry (CV), chronocoulometry (CC) and optical studies. The transmittance modulations or optical density differences during the coloring/bleaching process were found to be increased with the film thickness. This increment in optical differences led to an increase in coloration efficiency (CE) to about 95cm2/C, which is two times more than that observed in KOH and response time of 2.9s for bleaching (reduction) and 3.5s for coloration (oxidation) observed for the film deposited at 60min with excellent electrochemical stability up to 3000 c/b cycles in LiClO4-PC electrolyte.

Pine-cone morphology and pseudocapacitive behavior of nanoporous nickel oxide

Nanoporous pine-cone structured NiO powder was prepared by hydrothermally heated homogeneous precipitation method using cetyltrimethylammonium bromide surfactant (CTAB) as a template and urea as hydrolysis controlling agent. The NiO powder sample was characterized by thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), Brunauer–Emmet–Teller (BET) isotherm, scanning electron microscopy (SEM) and electrochemical measurements. The prepared NiO was found to be crystalline and highly porous in nature with high specific surface area and pore volume. The pseudocapacitance behavior of this material was investigated using cyclic voltammetry, chronopotentiometry and impedance spectroscopic studies employing a three-electrode system in the single cell mode. The SEM analysis reveals hierarchically porous pine-cone morphology for NiO which shows good specific capacitance (∼337 F g −1) measured by cyclic voltammetry. The galvanostatic charge–discharge cycles obtained in chronopotentiometric measurements indicate that the NiO sample exhibits good electrochemical stability. The columbic efficiency of NiO was found to be about 99% after 100 galvanostatic charge–discharge cycles. The impedance spectroscopic studies confirmed that the pseudocapacitance behavior of the porous NiO was a result of OH − ion diffusion processes in the system. In this study, a correlation has been made between the specific capacitance values and physicochemical properties as well as the unique surface morphology of NiO.

Morphological and structural studies of nanoporous nickel oxide films fabricated by anodic electrochemical deposition techniques

Porous nickel oxide films are directly deposited onto conducting indium tin oxide coated glass substrates by cyclic voltammetric (CV), galvanostatic, and potentiostatic strategies in a plating bath of sodium acetate, nickel sulfate, and sodium sulfate. By tuning the deposition parameters, it is possible to prepare nickel oxide films with various morphologies and structures. Film formation relies on the oxidation of dissolved Ni 2+ to Ni 3+, which further reacts with the available hydroxide ions from a slightly alkaline electrolyte to form insoluble nickel oxide/hydroxide deposits on the substrate. A compact film with particularly small pores is obtained by CV deposition in a potential range of 0.7–1.1 V. A galvanostatically deposited film is structurally denser near the surface of the substrate, and becomes less dense further away from the surface. Interestingly, a potentiostatically deposited film has pores distributed uniformly throughout the entire film. Therefore, for obtaining a uniform film with suitable pore size for electrolyte penetration, potentiostatic deposition technique is suggested. In addition, except for CV deposition, the deposited films resemble closely to cubic NiO when the annealing temperature exceeds 200 °C.

Electrodeposition of nanoporous nickel oxide film for electrochemical capacitors

Nanoporous nickel oxide film is electrochemically anodic deposited onto a stainless steel substrate by a plating bath of sodium acetate, nickel sulfate, and sodium sulfate mixture at room temperature without any template or catalyst. The deposited film is highly porous and composed of interconnected nanoflakes of thickness 12–16 nm after 300 ∘ C annealing. Specific capacitance of the deposited film depends on the applied potential window significantly in 1 M KOH solution. Specific capacitance is much increased by increasing the upper limit potential due to the contribution of redox reaction of nickel oxide to the measured capacitance. The deposited film shows a superior performance in high-rate charge/discharge capability. Specific capacitance of the deposited electrode is 167.3 Fg - 1 at 1 Ag - 1 charge/discharge, and 156.6 Fg - 1 at 16.5 Ag - 1 . The film also shows a stable capacitance during cycling. After 5000 test cycles at current density of 4 Ag - 1 , specific capacitance of the film is 140 Fg - 1 , approximately 87.5% of its maximum capacitance ( 160 Fg - 1 ) .

Novel Synthesis of Nanoporous Nickel Oxide and Nickel Nanoparticles/Amorphous Carbon Composites Using Soluble Starch as the Template

Abstract A simple and green synthetic route based on the use of soluble starch as the template has been utilized to prepare novel Ni(OH)2/starch precursors. Nanoporous nickel oxide (NiO) and nickel nanoparticles/amorphous carbon (Ni/C) composites have been successfully prepared by thermal decomposition of the novel Ni(OH)2/starch precursors in air and in nitrogen, respectively. N2 adsorption–desorption measurements show the two final products having nanoporous structures. The electrochemical measurements indicate that the nanoporous NiO sample has a favorable faradaic pseudocapacitance behavior.

A High Voltage Dye-sensitized Solar Cell using a Nanoporous NiO Photocathode

Abstract An np tandem dye-sensitized solar cell (np-DSC) comprising a titanium dioxide (TiO2) anode and a nickel oxide (NiO) cathode prepared as porous nanostructured films by a sol–gel method using a triblock copolymer template (P123, HO(OCH2CH2)20(OCH(CH3)CH2)70(OCH2CH2)20OH))CH2 exhibited a high open circuit voltage (Voc) of 0.92 V that surpassed the long time champion data, ≈0.8 V for conventional DSC.

SYNTHESIS OF WORMLIKE NANOPOROUS NICKEL OXIDE WITH NANOCRYSTALLINE FRAMEWORK FOR ELECTROCHEMICAL ENERGY STORAGE

In this work, nanoporous nickel oxide was synthesized using anionic surfactant assembly method. Structure characterizations show that this nickel oxide possesses partly-ordered mesoporous structure with nanocrystalline pore wall. The formation mechanism of wormlike nanoporous structure is ascribed to the quasi-reverse micelle system formed by ternary phases of SDS (sodium dodecyl sulfate)/urea/water. Cyclic voltammetry shows that these nickel oxide samples possess both good capacitive behavior due to its unique nanoporous structure and very high specific capacitance due to its high surface area with electrochemical activity.