A direct adsorption method for the synthesis of Cu2+-doped CdTe quantum dot (QD)-sensitized TiO2 nanotubes (TNTAs) for use as a photoanode is reported in this study. The influences of the molar concentration of Cu2+, the sensitization temperature, the sensitization time, and the loop index on the photovoltaic performance of the CdTe:Cu2+/TNTAswas investigated. Scanning electron microscopy images showed that the CdTe:Cu2+ QDs are well dispersed on the TNTA surface. UV–vis adsorption measurements showed that the visible absorption of the TNTAs was enhanced by the CdTe:Cu2+ QD sensitization. Whereas the power conversion efficiency (PCE) of the bare TNTAs was 0.11%, the maximum PCE of the CdTe:5%Cu2+/TNTAs was 3.70% with a sensitization time of 5.0 h, a sensitization temperature of 60 °C, and a loop index of 2. Therefore, CdTe:5%Cu2+/TNTAs may be employed in quantum-dot-sensitized solar cells.
Graphical abstract The conversion efficiency of the CdTe: 5%Cu2+/TiO2 nanotube arrays can reach a maximum of 3.7%, which is enhanced by 33-fold, on comparison with bare TiO2 nanotube arrays (0.11%).
A porous, hollow, microspherical composite of Li2MnO3 and LiMn1/3Co1/3Ni1/3O2 (composition: Li1.2Mn0.53Ni0.13Co0.13O2) was prepared using hollow MnO2 as the sacrificial template. The resulting composite was found to be mesoporous; its pores were about 20 nm in diameter. It also delivered a reversible discharge capacity value of 220 mAh g?1 at a specific current of 25 mA g?1 with excellent cycling stability and a high rate capability. A discharge capacity of 100 mAh g?1 was obtained for this composite at a specific current of 1000 mA g?1. The high rate capability of this hollow microspherical composite can be attributed to its porous nature.
We obtained Tannin-4-azobenzoic acid (azo dye) by the conventional method of diazotization and coupling of aromatic amines. The properties of the azo dye were characterized via ultraviolet-visible (UV–vis), infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy. Nanocrystalline titanium dioxide (TiO2) thin films were deposited by hydrothermal method onto fluorine-doped tin (IV) oxide (FTO)-coated glass substrate at 353 K for 4 h. The as-deposited and annealed films were characterized for structural, morphological, optical, thickness, and wettability properties. The synthesized metal free azo dye was used to sensitize the prepared TiO2 thin film with thickness of 26 μm. The photoelectrochemical (PEC) performance of TiO2 sensitized with the azo dye was evaluated in polyiodide (0.1 M KI + 0.01 M I2 + 0.1 M KCl) electrolyte at 40 mW cm?2 illumination intensity. The cell yielded a short circuit current of 2.82 mA, open circuit voltage of 314.3 mV, a fill factor of 0.30, and a photovoltaic conversion efficiency value of 0.64%.
Li[Ni1/3Co1/3Mn1/3]O2 (NCM 111) is a promising alternative to LiCoO2, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g?1 is quite low, and cycling at potentials above 4.5 V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO2 (R-3m, M?=?Ni, Co) and a shell of Li2MnO3 (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li+/Ni2+ cation disorder and stronger M*–O (M*?=?Mn, Co, Ni) bonds than NCM 111. The core–shell material Li1.15Na0.5(Ni1/3Co1/3)core(Mn1/3)shellO2 can be cycled to a high upper cutoff potential of 4.7 V, delivers a high discharge capacity of 218 mAh g?1 at 20 mA g?1, and retains 90 % of its discharge capacity at 100 mA g?1 after 90 cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density.
Graphical Abstract Average voltage vs. number of cycles for the core–shell and pristine materials at 20 mA g?1 for 10 cycles followed by 90 cycles at 100 mA g?1
The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide (LVP/N-RGO) composite was prepared by a facile one-pot hydrothermal method and evaluated as cathode material for lithium-ion batteries. It is clearly seen that the novel porous structure of the as-prepared LVP/N-RGO significantly facilitates electron transfer and lithium-ion diffusion, as well as markedly restrains the agglomeration of Li3V2(PO4)3 (LVP) nanoparticles. The introduction of N atom also has positive influence on the conductivity of RGO, which improves the kinetics of electrochemical reaction during the charge and discharge cycles. It can be found that the resultant LVP/N-RGO composite exhibits superior rate properties (92 mA h g?1 at 30 C) and outstanding cycle performance (122 mA h g?1 after 300 cycles at 5 C), indicating that nitrogen-doped RGO could be used to improve the electrochemical properties of LVP cathodes for high-power lithium-ion battery application.
Graphical abstract The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide composite with significantly accelerating electron transfer and lithium-ion diffusion exhibits superior rate property and outstanding cycle performance.
In this work, Bi3.64Mo0.36O6.55 nanoparticles (NPs) were successfully prepared by a facile hydrothermal method and utilized in pseudocapacitor for the first time. Within a redox potential range from ?1.0 to 0 V vs. Hg/HgO in a 1 M aqueous KOH solution by cyclic voltammetry (CV), chronopotentiometry (CP) and AC impendence, the specific capacitance could reach 998 F g?1 at 1 A g?1, which is possibly ascribed to the higher Bi content of Bi3.64Mo0.36O6.55 NPs. Furthermore, the Bi3.64Mo0.36O6.55 NP electrode exhibited good cycle stability maintaining over 85 % after 5000 cycles. These results demonstrated Bi3.64Mo0.36O6.55 NPs might be a promising electrode material for pseudocapacitor.
Graphical abstract The fabrication of uniform Bi3.64Mo0.36O6.55 nanoparticles with a diameter of 100 nm were succefully reported by a facial hydrothermal method, which exhibits a extraordinary electronic performance with 998 F g-1 at 1 A g-1 and cycling stability
The structural and electrochemical effects of electrospun V2O5 with selected redox-inactive dopants (namely Na+, Ba2+ and Al3+) have been studied. The electrospun materials have been characterised via a range of analytical methods including X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface area measurements and scanning and transmission electron microscopy. The incorporation of dopants in V2O5 was further studied with computational modelling. Structural analysis suggested that the dopants had been incorporated into the V2O5 structure with changes in crystal orientation and particle size, and variations in the V4+ concentration. Electrochemical investigations using potentiodynamic, galvanostatic and impedance spectroscopy analysis showed that electrochemical performance might be dependent on V4+ concentration, which influenced electronic conductivity. Na+- or Ba2+-doped V2O5 offered improved conductivities and lithium ion diffusion properties, whilst Al3+ doping was shown to be detrimental to these properties. The energetics of dopant incorporation, calculated using atomistic simulations, indicated that Na+ and Ba2+ occupy interstitial positions in the interlayer space, whilst Al3+ is incorporated in V sites and replaces a vanadyl-like (VO)3+ group. Overall, the mode of incorporation of the dopants affects the concentration of oxygen vacancies and V4+ ions in the compounds, and in turn their electrochemical performance.
Compared to other oxide materials, the sol-gel deposition of an optically transparent LiNbO3 waveguiding film of sufficient thickness (approx. 1?μm) is complicated by the presence of a highly hydrolyzing Nb(V) in the starting solution. Thicker films require more concentrated solutions that are not easily achieved for such ions. This problem may be solved using strong chelating agents such as water-soluble polymers. To prepare a stable Er(III)/Yb(III)/Li(I)/Nb(V)/2-methoxyethanol solution with high metal concentration, we tested three such polymers: polyethylene glycol (PEG), polyacrylic acid (PAA) and polyvinyl alcohol (PVA), and compared them with already used polyvinylpyrrolidone (PVP). The solutions were spin-coated on crystalline sapphire substrates under a multi-step heating-deposition regime. Apart from Er3+/Yb3+ photoluminescence properties, we evaluated the influence of the film microstructure (SEM, AFM) on optical transparency and waveguiding ability in the UV/Vis/NIR region (transmission and m-line spectroscopy). Among the newly tested polymers, only PEG was able to prevent Nb(V) hydrolysis up to a maximum metal concentration of 0.6?mol/L. For PEG and PVP, the crystallization temperature of the deposited films (between 700?°C and 1000?°C) was compared. After further optimization of the heating-deposition process, we were able to prepare a transparent Er3+/Yb3+:LiNbO3 film thick enough to guide an optical signal in the NIR region. Thus, the use of PEG results is one of the very few non-hydrolytic sol-gel methods suitable for the preparation of not only luminescent, but also waveguiding Er3+/Yb3+:LiNbO3 structures.
As a promising Li-ion battery cathode active material, lithium-rich manganese-based layer-structured oxides suffer from inferior cycle performance and poor rate capability. Herein, Nb-doped Li1.2Mn0.54Ni0.13Co0.13O2 is prepared by a sol-gel method, and the effects of Nb doping on its electrochemical performance are investigated. It is concluded that the Nb-doped Li1.2Mn0.54Ni0.13Co0.13O2, has a good layered structure along c-axis independent on the amount of Nb dopant and little cationic mixing. Nb doping for Li1.2Mn0.54Ni0.13Co0.13O2 has no obvious influence on its morphology. It is found that Nb doping can enhance the electrochemical activity of Li1.2Mn0.54Ni0.13Co0.13O2, such as improved rate performance and cycle performance under high rate conditions. Li1.2Mn0.54Ni0.13Co0.13O2 doped with 0.015 Nb shows the best cycle performance under the high rate with the capacity maintenance of 95.4% after 100 cycles under 5 C rate, which is higher than that of the undoped one by 10.5%.
The poor rate performance and low discharge capacity of LiCoO2 limit its applications. Therefore, in this work, we synthesized Li1-xMxCoO2 (M = Na, Zr, Nb) via solid-phase synthesis to improve its properties. X-ray diffraction (XRD) results suggest that the doping elements were successfully doped into LiCoO2. The electrochemical properties showed that the samples doped with the high-valence elements Zr and Nb had a higher capacity, better cycle stability, and better rate performance than those doped with the low-valence element Na. In particular, the capacity retention of LiCoO2, Li0.97Na0.03CoO2, Li0.99Zr0.01CoO2, and Li0.99Nb0.01CoO2 was 68, 42, 85, and 87%, respectively, after 80 cycles at a rate of 10 C at 55 °C. However, doping of Zr and Nb into the Li+ site of LiCoO2 will reduce the content of Li+. And, less Li+ extracted in the cathode material resulting in low discharge capacity under low current density. The larger radius of Na+ is incorporated into the Li slab and enlarged the interlayer spacing of the (003) plane. The larger (003) interplanar spacing can significantly facilitate the lithium diffusion and is also favorable to the rate capability. The differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis results demonstrated that the Zr-doped and Nb-doped LiCoO2 had a higher thermal stability in the charged state than the Na-doped LiCoO2. Additionally, the resistances of the Zr-doped and Nb-doped electrodes were much lower than that of the undoped electrode. Our research results indicate that doping with high-valence elements is a very effective strategy for optimizing the electrochemical performance of LiCoO2 and that this method can also be extended to other cathode materials.
MoS2 thin films with marigold flower-like nanostructures were grown on conductive fluorine-doped tin oxide (FTO) substrates through a one-step hydrothermal synthesis for their application as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). Different MoS2 thin film samples (A–D) were grown on FTO slides using different concentrations of precursors (sodium molybdate and thioacetamide), while keeping the Mo/S molar ratio constant (1:4.6), in all samples. The effect of varying precursor concentrations (3.2–12.6 mM on MoS2 basis) on the structure of the nanostructured thin films and their performance as DSSC-CEs was investigated. Scanning electron microscopy revealed a material with an infolded petal-like morphology. With increasing precursor concentration, the petal-like structures tended to form bunched nanostructures (100–300 nm) resembling marigold flowers. X-ray diffraction analysis, X-ray photoelectron, and Raman spectroscopy studies showed that the thin films were composed of hexagonal MoS2 with good crystallinity. Hall effect measurements revealed MoS2 to be a p-type semiconductor with a carrier mobility of 219.80 cm2 V?1 s?1 at room temperature. The electrochemical properties of the thin films were examined using cyclic voltammetry and electrochemical impedance spectroscopy. The marigold flower-like MoS2 thin films showed excellent electrocatalytic activity towards the I¯/I3¯ reaction and low charge transfer resistance (Rct) values of 14.77 Ω cm?1, which was close to that of Pt electrode (12.30 Ω cm?1). The maximum power conversion efficiency obtained with MoS2 CE-based DSSCs was 6.32%, which was comparable to a Pt CE-based DSSC (6.38%) under one sun illumination. Similarly, the maximum incident photon-to-charge carrier efficiency exhibited by MoS2 CE-based DSSCs was 65.84%, which was also comparable to a Pt CE-based DSSC (68.38%). The study demonstrated that the marigold flower-like nanostructured MoS2 films are a promising alternative to the conventional Pt-based CEs in DSSCs.
Free-standing and flexible NiMoO4 nanorods/reduced graphene oxide (rGO) membrane with a 3D hierarchical structure was successfully synthesized by a general approach including vacuum filtration followed by thermal reduction. NiMoO4 nanorods with about 50–100 nm diameter were embedded homogenously into the 3D rGO sheets and assembled with rGO to form a membrane about 10 μm in thickness. The NiMoO4/rGO membrane could be directly evaluated as anode materials for lithium-ion batteries (LIBs) without using binder. The 3D layer stacked graphene hierarchical architecture can not only offers a continuous conducting framework for efficient diffusion and transport of ion/electron but also accommodates the large volume expansion of NiMoO4 nanorod changes during cycling. Moreover, our results show that the NiMoO4/rGO membrane exhibited excellent electrochemical performance with a high reversible capacity of 945 mAh g?1 at a current density of 0.25 A g?1 as anode materials in LIBs.
A series of Ni0.37Co0.63S2-reduced graphene oxide nanocomposites with different graphene contents (NCS@rGO-x) has been successfully prepared via a facile one-step hydrothermal method and applied as the catalysts for the oxygen evolution reaction (OER) and degradation of organic pollutants. The XRD and FESEM analyses revealed that the phase structure and morphology of NCS nanoparticles were substantially influenced by the graphene contents. The phase structure of NCS nanoparticles gradually transformed from primary NiCo2S4 to Ni0.37Co0.63S2 and the morphology and size of NCS nanoparticles were found to become more regular and homogeneous with the increase of graphene concentration. On the NCS@rGO-x nanocomposites, the NCS@rGO-2 sample demonstrated the best catalytic activity toward the OER, which delivers a stable current density of 10 mA cm?2 at a small overpotential of ～276 mV (vs. RHE) with a Tafel slope as low as 48 mV dec?1. Furthermore, the NCS@rGO-2 sample showed the remarkable photocatalytic activity for degradation of methylene blue (MB), which may be attributed to the increased reaction sites and high separation efficiency of photogenerated charge carries due to the electronic interaction between NCS nanoparticles and rGO. All these impressive performances indicate that the NCS@rGO-2 nanocomposite is a promising catalyst in energy and environmental fields.
Graphical abstract A series of Ni0.37Co0.63S2-reduced graphene oxide nanocomposites with different graphene contents has been successfully prepared and applied as the catalysts for the oxygen evolution reaction (OER) and degradation of organic pollutants. The NCS@rGO-2 catalyst-modified stainless steel wire mesh (SSWM) electrode delivers a stable current density of 10 mA cm?2 at a small overpotential of ～276 mV (vs. RHE) with a Tafel slope as low as 48 mV dec?1. At the same time, the NCS@rGO-2 catalyst is also first investigated as an efficient photocatalyst for degradation of MB.
LiNi1-x-yCoxMnyO2 (NCM) with excessive lithium is known to exhibit high rate capability and charge–discharge cycling durability. However, the practical usage of NCM is difficult, because the positive electrode slurry is unstable and battery cells swell due to the alkaline residual lithium compound generated on the surface of NCM particles. To reduce the residual lithium compound, ammonium metatungstate (AMT) added to NCM is studied, and the effect is investigated by scanning electron microscopy, aberration-corrected scanning transmission electron microscopy, X-ray diffractometry, synchrotron X-ray diffractometry, and several electrochemical measurements. It is found that the AMT modification reduces the amount of alkaline residual lithium compound and improves the rate capability due to the ~1-nm-thick W-rich layer generated on the NCM surface.
The electron transport layer (ETL) plays a crucial role in the rapidly developed perovskite solar cells (PSCs). SnO2 has become one of the most promising alternatives to the TiO2 ETL due to its superior characteristics, such as the wider bandgap and hysteresis-free. However, at this stage, a lot of preparation methods of SnO2 ETL exist in high temperature and long time, those undoubtedly increase the cost and time of preparation. Herein, we report a low-temperature solution-processed SnO2 ETL without high annealing temperature, and a special bromine salt is used to modify SnO2, which leads to a higher transmittance and improved carrier transport ability. Due to the excellent optical and electrical properties, the photoelectric conversion efficiency of the prepared PSC reaches up to 18.8%. Moreover, it can be fabricated using facile solution processing at low temperature, making it particularly attractive for flexible development and low-cost commercialization.
A series of PANI-CNTs/TiO2 nanotubes/Ti electrodes were fabricated via pulse current co-electrodeposition of polyaniline and functionalized carbon nanotubes onto TiO2 nanotubes/Ti electrodes. FT-IR spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy were applied in order to characterize the modified TiO2 nanotubes/Ti electrodes. The morphology studies showed that the PANI-CNTs/TiO2 nanotubes/Ti nanocomposite electrode has many interlaced PANI-CNTs nanorods on the surface of TiO2 nanotubes. The electrochemical measurements of the modified electrodes confirmed that the CNTs in the composite can significantly improve the capacitive behavior as well which have been compared with that of PANI/TiO2 nanotubes/Ti electrodes. The modified electrode exhibited much higher specific capacitance (190 mF cm?2 with 90% retention after 1000 cycles) compared to the PANI/TiO2 nanotubes/Ti (70 mF cm?2 with 77% retention after 1000 cycles) at a current density of 0.85 mA cm?2, indicating its great potential for supercapacitor applications.
Co2(OH)3Cl xerogel interconnected mesoporous structures have been prepared by a facile one pot sol-gel process and heat treated at 200 and 400 °C. All samples are studied for their morphology, structure, and electrochemical stability upon cycling. The specific capacitance of the as-prepared Co2(OH)3Cl from single electrode study is 450 F/g, when the electrodes are cycled in 3 M KOH at a specific current 2 A/g. Interestingly, capacity retention after 500 and 1000 cycles is about 92 and 75 %, respectively. Sample heated at 200 °C exhibits 308 F/g at 2 A/g and that heated at 400 °C shows only 32 F/g at 0.2 A/g. With an increase in preparation temperature, amorphous Co2(OH)3Cl is converted to crystalline Co3O4 phases with lower electrochemical performance. In full cell study, as-prepared Co2(OH)3Cl showed a capacity of about 49 F/g as asymmetric capacitor and 32 F/g as symmetric capacitor at 2 A/g current density. Co2(OH)3Cl being a novel porous material with merits of homogeneous porosity, high surface area, and an interconnected three dimensional (3D) structure exhibits considerably high capacitance. With a significant specific capacity and electrochemical stability, the synthesized material is a novel potential candidate for supercapacitors.
LiMn2O4 is one of the most promising cathode materials due to its high abundance and low cost. However, the practical application of LiMn2O4 is greatly limited owing to its low volumetric energy density. Therefore, increasing its energy density is an urgent problem to be resolved. Herein, using the simple and mass production preferred solid-state reaction, surficial Nb-doped LiMn2O4 composed of the truncated octahedral or spherical-like primary particles are successfully synthesized. Auger electron spectroscopy (AES) and X-ray diffraction (XRD) characterizations confirm that most of Nb5+ enrich in the surficial layer of the particles to form a LiMn2-xNbxO4 phase. This kind of doping can increase the specific discharge capacity of LiMn2O4 materials. Contrast with the pristine LiMn2O4, the discharge capacity of LiMn1.99Nb0.01O4-based 18650R-type battery increases from 1497 to 1705 mAh with the volumetric energy density increasing by ~?13.9%, benefiting from the joint increments of the specific discharge capacity from 119.5 to 123.7 mAh g?1 and the compacted density from 2.81 to 3.10 g cm?3. Furthermore, the capacity retention after 500 cycles at 1 C (1500 mA) is also improved by 17.1%.
The effect of dip time variations on electrochemical performance of polypyrrole (PPy)-copper hydroxide hybrid thin-film electrodes was studied well in depth. Synthesis was carried out using a successive ionic layer adsorption and reaction (SILAR) method via an aqueous route, using 0.1 M pyrrole, 0.1 M Cu(NO3)2, and H2O2. The electrochemical analysis was made by using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) analysis, and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) image of optimized electrode shows nanolamellae-like structures. The characteristic peak observed in Fourier transform infrared (FTIR) analysis at 1558 cm?1 validates the existence of PPy in hybrid electrode material, while the peaks observed at 21.5° and 44.5° in X-ray diffraction (XRD) patterns are evidence for triclinic Cu(OH)2. The observed maximum values of specific capacitance (SC), specific power (SP), specific energy (SE), and coulombic efficiency (η) of the optimized electrode are 56.05 F/g, 10.48 Wh/kg, 11.11 kW/kg, and 46.47%, respectively. For originality and value, the SILAR synthesis of PPy-Cu(OH)2 hybrid thin-film electrodes was carried out for the very first time. Synthesized electrodes showed improved surface structures and electrochemical stability than the pristine PPy electrodes which are necessary for the supercapacitive applications.
Cuprous oxide (Cu2O) thin films have been deposited onto fluorine doped tin oxide (FTO) glass substrates by using electrochemical route. The structural, morphological, and chemical composition of the deposited films have been studied by using X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Energy dispersive x-ray spectroscopy (EDAX) techniques respectively. The optical studies have been carried out by using UV-Vis spectroscopy. The effect of potential, pH and bath temperature onto absorption and band gap of Cu2O thin films have been studied. The highest sensitivity 6.25 mA·mM·cm-2 is observed for the thin films which shows glucose concentration 7 mM in 0.1 M NaOH solution. The results indicates Cu2O is promising material for glucose sensor with high sensitivity, high stability, and repeatability.
Graphical abstract The surface morphology of Cu2O thin films was found to be tip-truncated octahedral. The films were prepared by electrodeposition. The Cu2O thin films were used to construct low cost, highly sensitive and stable glucose sensor.
