On the performances of CuxO-TiO2 (x = 1, 2) nanomaterials as innovative anodes for thin film lithium batteries

Hydrogen Gas Sensing Properties of Mixed Copper-Titanium Oxide Thin Films

Hydrogen is an efficient source of clean and environmentally friendly energy. However, because it is explosive at concentrations higher than 4%, safety issues are a great concern. As its applications are extended, the need for the production of reliable monitoring systems is urgent. In this work, mixed copper-titanium oxide ((CuTi)Ox) thin films with various copper concentrations (0-100 at.%), deposited by magnetron sputtering and annealed at 473 K, were investigated as a prospective hydrogen gas sensing material. Scanning electron microscopy was applied to determine the morphology of the thin films. Their structure and chemical composition were investigated by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The prepared films were nanocrystalline mixtures of metallic copper, cuprous oxide, and titanium anatase in the bulk, whereas at the surface only cupric oxide was found. In comparison to the literature, the (CuTi)Ox thin films already showed a sensor response to hydrogen at a relatively low operating temperature of 473 K without using any extra catalyst. The best sensor response and sensitivity to hydrogen gas were found in the mixed copper-titanium oxides containing similar atomic concentrations of both metals, i.e., 41/59 and 56/44 of Cu/Ti. Most probably, this effect is related to their similar morphology and to the simultaneous presence of Cu and Cu₂O crystals in these mixed oxide films. In particular, the studies of surface oxidation state revealed that it was the same for all annealed films and consisted only of CuO. However, in view of their crystalline structure, they consisted of Cu and Cu₂O nanocrystals in the thin film volume.

High-performance Ti-doped ZnS thin film anode for lithium-ion batteries

Thin film microbattery is urgently needed to provide a long-term stable on-chip power for various kinds of microdevices or microsystems. Anode is a core component in thin film lithium ion microbattery, however, previous researches mostly focused on metal oxide or Si-based thin film anodes, and the reports of metal sulfide thin film anodes are limited. Herein, we present a new type of Ti-doped ZnS thin film fabricated by radio frequency (RF) magnetron co-sputtering. The Ti doping is designed to enhance the overall electrical conductivity of the ZnS thin film, since the insulation of ZnS is one of the major barriers to deliver its lithium storage performance. As an anode applied in lithium ion battery, the Ti-doped ZnS thin film exhibits good cycling stability up to 500 cycles at a current density of 1.0 A·g^-1, and remains a higher specific capacity of 463.1 mAh·g^-1than that of the pure ZnS thin film, showing its better electrochemical reaction reversibility. The rate capability and EIS measurements manifest the more favorable electrochemical reaction kinetics of the Ti-doped ZnS thin film, moreover, the CV tests at various scan rates indicate the improved Li⁺diffusion kinetics in the electrode after Ti doping.

Chemiresistors Based on Li-Doped CuO–TiO2 Films

Chemiresistors based on thin films of the Li-doped CuO–TiO2 heterojunctions were synthesized by a 2-step method: (i) repeated ion beam sputtering of the building elements (on the Si substrates and multisensor platforms); and (ii) thermal annealing in flowing air. The structure and composition of the films were analyzed by several methods: Rutherford Backscattering (RBS), Neutron Depth Profiling (NDP), Secondary Ion Mass Spectrometry (SIMS), and Atomic Force Microscopy (AFM), and their sensitivity to gaseous analytes was evaluated using a specific lab-made device operating in a continuous gas flow mode. The obtained results showed that the Li doping significantly increased the sensitivity of the sensors to oxidizing gases, such as NO2, O3, and Cl2, but not to reducing H2. The sensing response of the CuO–TiO2–Li chemiresistors improved with increasing Li content. For the best sensors with about 15% Li atoms, the detection limits were as follows: NO2 → 0.5 ppm, O3 → 10 ppb, and Cl2 → 0.1 ppm. The Li-doped sensors showed excellent sensing performance at a lower operating temperature (200 °C); however, even though their response time was only a few minutes, their recovery was slow (up to a few hours) and incomplete.

Heterostructure Cu2O/(001)TiO2 Effected on Photocatalytic Degradation of Ammonia of Livestock Houses

In this paper, a heterogeneous composite catalyst Cu2O/(001)TiO2 was prepared by the impregnation-reduction method. The crystal form, highly active facet content, morphology, optical properties, and the photogenerated electron-hole recombination rate of the as-prepared catalysts were investigated. The performance of Cu2O/(001)TiO2 was appraised by photocatalytic degradation of ammonia under sunlight and was compared with lone P25, Cu2O, and (001)TiO2 at the same reaction conditions. The results showed that 80% of the ammonia concentration (120 ± 3 ppm) was removed by Cu2O/(001)TiO2, which was a higher degradation rate than that of pure P25 (12%), Cu2O (12%), and (001)TiO2 (15%) during 120 min of reaction time. The reason may be due to the compound’s (Cu2O/(001)TiO2) highly active (001) facets content that increased by 8.2% and the band gap width decreasing by 1.02 eV. It was also found that the air flow impacts the photocatalytic degradation of ammonia. Therefore, learning how to maintain the degradation effect of Cu2O/(001)TiO2 with ammonia will be important in future practical applications.

Rapid design of a core–shell-like metal hydroxide/oxide composite and activated carbon from biomass for high-performance supercapattery applications

Core–shell-like 2D Ni(OH)₂ on a Cu₂O custard apple-like composite and biomass-derived activated carbon materials were used for the construction of a supercapattery device.

Atomic layer deposition of Cu(i) oxide films using Cu(ii) bis(dimethylamino-2-propoxide) and water

To grow films of Cu₂O, bis-(dimethylamino-2-propoxide)Cu(ii), or Cu(dmap), is used as an atomic layer deposition precursor using only water vapor as a co-reactant. Between 110 and 175 °C, a growth rate of 0.12 ± 0.02 Å per cycle was measured using an in situ quartz crystal microbalance (QCM). X-ray photoelectron spectroscopy (XPS) confirms the growth of metal-oxide films featuring Cu(i).

Enhanced photoelectrochemical and photocatalytic activity by Cu2O/SrTiO3 p–n heterojunction via a facile deposition–precipitation technique

In our study, a new visible-light-driven photocatalyst Cu₂O/SrTiO₃ (C/S) heterojunction was firstly prepared by a simple, facile and effective deposition–precipitation technique.

Evaluation of undoped and M-doped TiO2, where M = Sn, Fe, Ni/Nb, Zr, V, and Mn, for lithium-ion battery applications prepared by the molten-salt method

Bare and Fe, Zr, Sn, Mn, V and Ni/Nb doped TiO₂ prepared by the molten salt method, amongst these the Zr-doped sample exhibited a stable reversible capacity.

Influence of Mn incorporation on the supercapacitive properties of hybrid CuO/Cu(OH)2 electrodes

Variation of specific capacitance of undoped and Mn doped CuO/Cu(OH)₂ hybrid electrodes with corresponding SEM.

Decoration of size-tunable CuO nanodots on TiO2 nanocrystals for noble metal-free photocatalytic H2 production

We report a simple yet effective approach for the decoration of the TiO2 nanocrystal surface with size-tunable CuO nanodots for high-performance noble metal-free photocatalytic H2 production. Modification with polyacrylic acid enables the surface of TiO2 nanocrystals to be selectively deposited with Cu(OH)2 nanodots, which can be subsequently converted to CuO through dehydration without changing their morphologies. UV irradiation of the nanocomposite solution in the presence of a hole scavenger produces photogenerated electrons which reduce CuO to metallic Cu nanodots, making them effective co-catalysts in a role similar to Pt for promoting photocatalytic H2 production. Due to the considerably high work function of Cu, the formation of a metal-semiconductor Schottky junction induces efficient charge separation and transfer. As a result, the TiO2 nanocrystals decorated with an optimal amount of CuO nanodots (1.7 wt%) could reach ∼50% of the photocatalytic activity achievable by the Pt-TiO2 counterparts (1 wt%), clearly demonstrating the great potential of such composite catalysts for efficient noble metal-free photocatalytic H2 production.

MnO2 prepared by hydrothermal method and electrochemical performance as anode for lithium-ion battery

Two α-MnO2 crystals with caddice-clew-like and urchin-like morphologies are prepared by the hydrothermal method, and their structure and electrochemical performance are characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), galvanostatic cell cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The morphology of the MnO2 prepared under acidic condition is urchin-like, while the one prepared under neutral condition is caddice-clew-like. The identical crystalline phase of MnO2 crystals is essential to evaluate the relationship between electrochemical performances and morphologies for lithium-ion battery application. In this study, urchin-like α-MnO2 crystals with compact structure have better electrochemical performance due to the higher specific capacity and lower impedance. We find that the relationship between electrochemical performance and morphology is different when MnO2 material used as electrochemical supercapacitor or as anode of lithium-ion battery. For lithium-ion battery application, urchin-like MnO2 material has better electrochemical performance.

Thorough characterization of sputtered CuO thin films used as conversion material electrodes for lithium batteries

CuO thin films were prepared by radio frequency magnetron sputtering using a copper target in a (Ar + O2) reactive mixture. Different sputtering parameters were varied including oxygen flow rate, total pressure, target-substrate distance, substrate temperature and target orientation. As expected, the thin film chemical composition is strongly dependent on the oxygen flow rate. CuO thin films having a good electronic conductivity (9.3 × 10(-1) S·cm(-1)) were obtained with an oxygen concentration of 12%. The texture and the columnar growth are amplified when the target is tilted. Preliminary electrochemical results highlight that CuO thin film performances in lithium systems are tightly related to their morphology and structure.

Sol–gel deposited Cu2O and CuO thin films for photocatalytic water splitting

Cu₂O and CuO thin films deposited by a sol–gel spin-coating process show promise for photocatalytic water splitting.

Integrated solid/nanoporous copper/oxide hybrid bulk electrodes for high-performance lithium-ion batteries

Nanoarchitectured electroactive materials can boost rates of Li insertion/extraction, showing genuine potential to increase power output of Li-ion batteries. However, electrodes assembled with low-dimensional nanostructured transition metal oxides by conventional approach suffer from dramatic reductions in energy capacities owing to sluggish ion and electron transport kinetics. Here we report that flexible bulk electrodes, made of three-dimensional bicontinuous nanoporous Cu/MnO2 hybrid and seamlessly integrated with Cu solid current collector, substantially optimizes Li storage behavior of the constituent MnO2. As a result of the unique integration of solid/nanoporous hybrid architecture that simultaneously enhances the electron transport of MnO2, facilitates fast ion diffusion and accommodates large volume changes on Li insertion/extraction of MnO2, the supported MnO2 exhibits a stable capacity of as high as ~1100 mA h g(-1) for 1000 cycles, and ultrahigh charge/discharge rates. It makes the environmentally friendly and low-cost electrode as a promising anode for high-performance Li-ion battery applications.

Diffusion-controlled evolution of core-shell nanowire arrays into integrated hybrid nanotube arrays for Li-ion batteries

Controlled integration of multiple semiconducting oxides into each single unit of ordered nanotube arrays is highly desired in scientific research for the realization of more attractive applications. We herein report a diffusion-controlled solid-solid route to evolve simplex Co(CO3)0.5(OH)0.11H2O@TiO2 core-shell nanowire arrays (NWs) into CoO-CoTiO3 integrated hybrid nanotube arrays (NTs) with preserved morphology. During the evolution procedure, the decomposition of Co(CO3)0.5(OH)0.11H2O NWs into chains of CoCO3 nanoparticles initiates the diffusion process and promotes the interfacial solid-solid diffusion reaction even at a low temperature of 450 °C. The resulting CoO-CoTiO3 NTs possess well-defined sealed tubular geometries and a special "inner-outer" hybrid nature, which is suitable for application in Li-ion batteries (LIBs). As a proof-of-concept demonstration of the functions of such hybrid NTs in LIBs, CoO-CoTiO3 NTs are directly tested as LIB anodes, exhibiting both a high capacity (~600 mA h g(-1) still remaining after 250 continuous cycles) and a much better cycling performance (no capacity fading within 250 total cycles) than CoO NWs. Our work presents not only a diffusion route for the formation of integrated hybrid NTs but also a new concept that can be employed as a general strategy to fabricate other oxide-based hybrid NTs for energy storage devices.

Li-cycling properties of molten salt method prepared nano/submicrometer and micrometer-sized CuO for lithium batteries

We report the synthesis of CuO material by molten salt method at a temperature range, 280 to 950 °C for 3 h in air. This report includes studies on the effect of morphology, crystal structure and electrochemical properties of CuO prepared at different temperatures. Obtained CuO was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area methods. Samples prepared at ≥410 °C showed a single-phase material with a lattice parameter value of a = 4.69 Å, b = 3.43 Å, c = 5.13 Å and surface area values are in the range 1.0-17.0 m(2) g(-1). Electrochemical properties were evaluated via cyclic voltammetry (CV) and galvanostatic cycling studies. CV studies showed a minor difference in the peak potentials depending on preparation temperature and all compounds exhibit a main anodic peak at ~2.45 V and cathodic peaks at ~0.85 V and ~1.25 V vs Li. CuO prepared at 750 °C showed high and stable capacity of ~620 mA h g(-1) at the end of 40th cycle.

CuO/Cu2O composite hollow polyhedrons fabricated from metal-organic framework templates for lithium-ion battery anodes with a long cycling life

Novel CuO/Cu2O hollow polyhedrons with porous shells were fabricated by thermal decomposition of coordination compound [Cu3(btc)2]n (btc = benzene-1,3,5-tricarboxylate) polyhedrons at 350 °C. When tested as anode materials for lithium-ion batteries, these hollow polyhedrons exhibited a reversible lithium storage capacity as high as 740 mA h g(-1) at 100 mA g(-1) after 250 cycles even if the charge-discharge process is stopped for one week during the test time.

Colloidal synthesis of cuprite (Cu2O) octahedral nanocrystals and their electrochemical lithiation

We report a facile colloidal route to prepare octahedral-shaped cuprite (Cu2O) nanocrystals (NCs) of ∼40 nm in size that exploits a new reduction pathway, i.e., the controlled reduction of a cupric ion by acetylacetonate directly to cuprite. Detailed structural, morphological, and chemical analyses were carried on the cuprite NCs. We also tested their electrochemical lithiation, using a combination of techniques (cyclic voltammetry, galvanostatic, and impedance spectroscopy), in view of their potential application as anodes for Li ion batteries. Along with these characterizations, the morphological, structural, and chemical analyses (via high-resolution electron microscopy, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy) of the cycled Cu2O NCs (in the lithiated stage, after ∼50 cycles) demonstrate their partial conversion upon cycling. At this stage, most of the NCs had lost their octahedral shape and had evolved into multidomain particles and were eventually fragmented. Overall, the shape changes (upon cycling) did not appear to be concerted for all the NCs in the sample, suggesting that different subsets of NCs were characterized by different lithiation kinetics. We emphasize that a profound understanding of the lithiation reaction with NCs defined by a specific crystal habit is still essential to optimize nanoscale conversion reactions.