Composite Thin Film Electrodes Research Articles

N-doping SrTiO3@SrCO3 heterostructure electrode: Synthesis, electrochemical characterization, and varistor application

Abstract Optical traditional techniques, such as diffusive reflectance spectroscopy, are used to confirm absorption behavior modification after anion doping process. However, the doping process in some materials as a SrTiO 3 semiconductor was not clearly proved in different anions doping cases through traditional techniques. In this case, supporting technique as electrochemical measurements could prove a great help in elucidating the doping process modifications in the semiconductor material. In this paper, the electrochemical characterization was applied to analyze changes in energy bands produced by N-doping in SrTiO 3 @SrCO 3 composite thin film electrodes. SrTiO 3 @SrCO 3 and N-doped SrTiO 3 @SrCO 3 nanoparticles were first characterized by X-ray diffraction to confirm a perovskite crystalline structure in both materials, whereas diffusive reflectance spectroscopy was used to demonstrate that no modification in the absorption spectrum is evident after doping. The thin films were observed by FESEM/SEM, and its deposition parameters were electrochemically evaluated. The electrochemical profiles of SrTiO 3 @SrCO 3 and N doped SrTiO 3 @SrCO 3 thin film electrodes were compared in dark and under UV-C light to determine the photocurrent. These measurements presented distinct results for the undoped and the doped materials, such as modification in photocurrent under UV-C illumination. SrTiO 3 @SrCO 3 composite electrodes show important characteristics which could be classified as a potential candidate in varistor uses, especially in the low-voltage protection system. The presented results confirm that electrochemical methods are useful to analyze the synthesis efficiency to produce N-doped structures.

Porous NiO/graphene composite thin films as high performance anodes for lithium-ion batteries

Porous NiO and NiO/graphene (NiOG) thin film electrodes were prepared by electrostatic spray deposition (ESD) technique and investigated as anodes for lithium ion batteries. The porous NiO structure was designed to better buffer the mechanical stress induced by the volume change of NiO as well as inhibit the aggregation of nanoparticles during conversion reaction. Aiming to facilitate better reaction kinetics compared to pure NiO electrode, graphene nanoplates were added to form NiOG composite film where additional graphene could be helpful for the electron transfer as conductive medium. As a result, porous NiOG composite thin film electrode exhibits high rate capability (759, 774, 614, 447, 243 and 104mAhg−1 at 0.1, 0.2, 0.5, 1, 2, and 5Ag−1, respectively) and excellent cycling performance (no capacity decrease for 500 cycles at 0.5Ag−1). From analyzing cyclic voltammetry (CV) curves, rate and cyclical performance, and electrochemical impedance spectroscopy (EIS), it was concluded that NiOG composite electrodes exhibited enhanced electrochemical performance compared to NiO electrodes.

Free-standing silver/carbon nanotube metal matrix composite thin films

Advanced metal matrix composite (MMC) thin-film electrodes were fabricated utilizing single-wall carbon nanotubes (SWCNTs) as a reinforcement material. The MMCs were embedded with SWCNT thin films of 10, 20, and 50 nm thicknesses between thermally evaporated 1.5 µm Ag layers. A method has been developed to release the MMCs as free-standing films, and tensile testing was performed to evaluate the mechanical properties. The MMC containing a 20-nm SWCNT layer achieved a ~30 % increase in ultimate tensile strength, and a ~100 % increase in strain-to-failure, resulting in a ~150 % increase in toughness compared to Ag control samples. Scanning electron microscopy (SEM) analysis of the MMC microstructure revealed a decrease in Ag grain size with increased SWCNT loading, which correlated with the mechanical performance to identify the critical range of SWCNT layer thicknesses to achieve reinforcement. SEM also revealed SWCNTs protruding more than 1 μm from the fracture edges, indicating the potential of the MMCs to bridge micro-cracks in electrodes. The collective results show promise for SWCNT MMCs as an advanced electrode material capable of bridging micro-cracks in solar cells and flexible electronics.

Enhanced specific capacitance and supercapacitive properties of polyaniline–iron oxide (PANI–Fe2O3) composite electrode material

In the present work we report ferric oxide (α-Fe2O3) and conducting polyaniline–ferric oxide (PANI–Fe2O3) composite thin films prepared using simple electrodeposition technique. The structural and morphological analysis was carried out by X-ray diffraction and scanning electron microscopy. The supercapacitive properties of these films were examined using cyclic voltammetry, charge–discharge studies, and electrochemical impedance spectroscopy in 0.5 M Na2SO4 electrolyte. It is observed that the PANI–Fe2O3 composite electrode delivered higher specific capacitance than individual α-Fe2O3. Also the composite thin film electrode exhibits excellent specific capacitance retention of about 87 % over 1000 CV scan cycles as compared to α-Fe2O3 electrode, which exhibits only 84 % retention capacity.

SILAR deposited porous polyaniline-titanium oxide composite thin film for supercapacitor application

The present investigation shows the facile preparation of porous polyaniline-titanium oxide composite nanofibers using a successive ionic layer adsorption and reaction (SILAR) method. The result of X-ray diffraction indicates the amorphous nature of polyaniline-titanium oxide (PANI-TiO2) composite nanofibers. Fourier transform infrared (FT-IR) and FT-Raman spectroscopy studies reveal the formation of composite material. The morphology of PANI-TiO2 composite observed using scanning electron microscope (SEM) shows the spherical TiO2 nanoparticles grown on the PANI nanofibers. The electrochemical measurement shows PANI-TiO2 composite electrode yields specific capacitance of 776Fg−1 and gives higher capacitance retention (83%) over 5000 cycles. The superior electrochemical properties attributed to the porous structure of PANI-TiO2 composite nanfibers as well as the synergistic effect between conducting PANI nanofiber and TiO2 nanoparticles. This specifies that this method may provide a promising strategy for preparation of PANI-based transition metal oxide composite thin film electrodes for better performance of supercapcitor.

Pulsed Laser Deposited Sns-Snse Composite Thin Film As a New Anode Material for Lithium Storage

In recent years tin-based materials has been subjected as promising anode materials due to a high theoretical capacity of Li4.4Sn (994mAh g-1). However, tin-based materials is still far away from practical use since it suffers from significant volume change. It has been demonstrated that nano-thin film have its unique characteristics than bulk materials. In this work, SnS-SnSe composite thin films are synthesized by plused laser deposition. Its first discharge capacity was 1225.8 mAh g-1 and capacity after three cycles maintained about 650 mAh g-1. SnS-SnSe composite thin film firstly reacted with Li during discharge to form Li2SALi2Se and Sn, then Sn reacted with Li to form LixSn alloy. During the charge, LixSn firstly decomposed to form elementary Sn, then Sn catalyzed Li2S and Li2Se to decompose to rebuild SnS-SnSe composite thin film. Li2S and Li2Se produced during discharge can suffer a certain amount of volume change which enhanced the cycle performance. SnS-SnSe composite thin film had more grain boundary than SnS or SnSe thin film which could effectively enhance electrochemical activity and increase capacity. Fig.1 The first three CVs of SnS-SnSe composite thin film Fig.2 Galvanostatic charge-discharge curve of SnS-SnSe composite thin film electrodes Fig.3 Cycling performance of SnS-SnSe, SnS and SnSe thin films with 20 cycles Acknowledgements The authors appreciate the financial support of LPMT, CAEP (ZZ13007), Project 2013A030214 supported by CAEP. Figure 1

Preparation of TiO2-based nanotubes/nanoparticles composite thin film electrodes for their electron transport properties

The composite thin film electrodes were prepared with one-dimensional (1D) TiO2-B nanotubes (NTs) and zero-dimensional TiO2 nanoparticles (NPs) based on different weight ratios. The electron transport properties of the NTs/NPs composite thin film electrodes applied for dye-sensitized solar cells had been investigated systematically. The results indicated that although the amount of dye adsorption decreased slightly, the devices with the NTs/NPs composite thin film electrodes could obtain higher open-circuit voltage and overall conversion efficiency compared to devices with pure TiO2 NPs electrodes by rational tuning the weight ratio of TiO2-B NTs and TiO2 NPs. When the weight ratio of TiO2-B NTs in the NTs/NPs composite thin film electrodes increased, the density of states and recombination rate decreased. The 1D structure of TiO2-B NTs can provide direct paths for electron transport, resulting in higher electron lifetime, electron diffusion coefficient and electron diffusion length. The composite thin film electrodes possess the merits of the rapid electron transport of TiO2-B NTs and the high surface area of TiO2 NPs, which has great applied potential in the field of photovoltaic devices.

Nitrite ion sensing properties of ZnTiO3–TiO2 composite thin films deposited from a zinc–titanium molecular complex

ZnTiO3–TiO2 composite thin film electrode has been fabricated by AACVD method and tested for electrochemical nitrite ion detection.

Platinum–zirconium composite thin film electrodes for high-temperature micro-chemical sensor applications

Stable metal interconnect thin films are critical in the development of various micro-machined devices that may operate continuously at elevated temperatures. The main objective of this work was to investigate the microstructural and electrical stability of a functionally gradient platinum (Pt)–zirconium (Zr) composite thin film electrode designed for resistive-type chemical sensors. Thin film electrodes were fabricated using a DC magnetron sputtering process. Zirconium was used as both the conventional adhesion promoter and the Pt grain modifier within the bulk electrode microstructure. The thin film deposition was completed on highly polished alumina substrates at 200°C. The various composite Pt thin films were further annealed at 1200°C after deposition for 1–24h for rapid evaluation of the microstructure stability. This temperature was chosen since the electrodes are expected to operate beyond 1000°C for high-temperature MEMS applications. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were conducted to characterize the alterations in chemistry, microstructure and distribution of the constituent elements through the film thickness. The electrical resistivity of the as-deposited and thermally processed Pt thin films was measured by utilizing a van der Pauw's four-point probe technique. The work identified a Zr/Zr+Pt/Pt composite thin film with the 525nm total film thickness that demonstrated resistivity <5.08×10−7Ωm after being processed to 1200°C for 15h. A lift-off technique was finally used to produce a micro-electrode patterns with the optimized film structure for high-temperature applications.

Tunable Optical Properties of Carbon Nanotube Composite Thin Films

Novel transparent composite thin film electrodes with embedded multi-walled carbon nanotubes (MWCNTs) were fabricated in this study. Their optical properties were explored for applications as cathodes in optoelectronic devices, such as solar cells. The optical properties of the MWCNTs composite thin film were measured in the UV-Vis and IR regions. The films fabricated had tunable transparency from 85% to 80% at 550nm. In the IR region the absorption maxima were at 1151nm, 1203nm, 1223nm, and 1630nm. The band-gap of the films was 3.82 and complementary to the band-gaps of common conjugated polymers for organic solar cells.

Polyaniline nanofibers–graphene oxide nanoplatelets composite thin film electrodes for electrochemical capacitors

A facile electrochemical method was applied to synthesize graphene oxide nanoplatelets and polyaniline nanofiber composite thin film electrodes for supercapacitors.

Charge storage properties of a α-MoO3/carboxyl-functionalized single-walled carbon nanotube composite electrode in a Li ion electrolyte

A facile, cost-effective and scaleable method is presented for the fabrication of thin film α-MoO3/SWCNT-COOH composite electrodes with a high charge storage capacity in LiClO4/propylene carbonate in a 1.5–3.5V (versus Li/Li+) working electrochemical window. α-MoO3 nanobelts were synthesized using an established hydrothermal method and composite thin film electrodes incorporating interwoven single walled carbon nanotubes as an electrical conductive additive within a network of α-MoO3 nanobelts were manufactured by spray deposition. The composite electrode showed a maximum charge storage/capacitance of 697.7Cg−1 (193.8mAhg−1)/ 348.7Fg−1 at 0.1mVs−1 (per unit mass of composite electrode) with a contribution to charge storage from capacitive and diffusion controlled processes of 443Cg−1 and 463.2Cg−1 (per unit mass of α-MoO3), respectively, which is comparable to charge storage attained by electrodes manufactured by more costly and non-scaleable templating methods previously reported. Cyclic voltammetry showed capacitances of 167Fg−1 and 75Fg−1 at 10mVs−1 and 50mVs−1, respectively, suggesting a potential application as electrochemical capacitor electrodes of moderate power densities. On the other hand, a charge storage of 697.7Cg−1 (193.8mAhg−1) attained at 0.1mVs−1, and a capacity of 596.8mAhg−1 achieved at 10mAg−1 in galvanostatic charge–discharge experiments supports a potential application of α-MoO3 as a Li-ion battery cathode.

Surface characteristics and photoelectrocatalytic capabilities of nanoporous titanium dioxide/tin indium oxide composite thin film electrodes

This study applied a prolonged DC magnetron sputtering technique to prepare two nanoporous columnar and well-crystallized titanium dioxide/tin indium oxide (TiO2/ITO) composite thin film electrodes for photoelectrocatalytic reactions. The visible light enabled TiO2/ITO electrode was obtained by carbon doping while sputtering thin-film TiO2 onto the proposed ITO substrate. Both photoelectrocatalytic hydrogen generation and dimethyl sulfoxides (DMSO) degradation experiments were conducted for evaluating the photoelectrocatalytic capabilities of the prepared samples. The contribution of ITO co-doping on photocatalytic activities of hetero-structured photocatalysts was investigated in the study. The experimental results show both samples primarily in anatase TiO2 crystallization phase. Due to a higher sputtering power is applied for carbon-doped TiO2/ITO (CTI) film preparation, the tin ions of ITO permeate into TiO2 film to form a crystalline Ti1−xSnxO2 interfacial layer, which results in CTI film with a higher photocatalytic oxidation rate of than the simple TiO2/ITO (STI). The dimethyl sulfoxides (DMSO) degradation rate by CTI is about 2.83-fold higher than by STI. Conversely, the STI, prepared at a lower sputtering power, produced much higher photocurrent density (∼230μAcm−2) and hydrogen yield rate (∼15.67μmolcm−2h−1) than the CTI owing to forming a higher Schottky barrier at the TiO2/ITO interface of STI film. These findings suggest that the interfacial characteristics of the TiO2/ITO film importantly affect their photocatalytic activities. This study also demonstrates that the prolonged DC magnetron sputtering technique can be applied to prepare thin-film photocatalysts with selective application purposes if suitable sputtering conditions can be carefully selected.

Dual role of carbon in the catalytic layers of perovskite/carbon composites for the electrocatalytic oxygen reduction reaction

Perovskite oxides are promising materials for the ORR in alkaline media. However, catalytic layers prepared from perovskite powders suffer from high Ohmic losses and low catalyst utilization. An addition of carbon to the catalytic layers greatly improves the performance of the electrodes in the ORR. In this work composite thin film electrodes comprised of a perovskite oxide (either LaCoO3 or La0.8Sr0.2MnO3) and pyrolytic carbon of the Sibunit family were investigated in aqueous 1M NaOH electrolyte using cyclic voltammetry and rotating disc electrode (RDE) method with the objective to unveil the influence of carbon on the catalyst utilization and on the ORR electrocatalysis. By systematically varying the oxide to carbon ratio we arrive to the conclusion on the dual role of carbon in composite electrodes. On the one hand, it is required to improve the electrical contact between perovskite particles and the current collector, and to ensure maximum utilization of the perovskite surface. On the other hand, carbon plays an active role in the ORR by catalyzing the O2 reduction to H2O2. Composite electrodes catalyze the 4e− ORR in contrast to carbon which is only capable of catalyzing the 2e− reduction. For LaCoO3 composite electrodes, carbon is responsible for the catalysis of the first steps of the ORR, the role of LaCoO3 being largely limited to the hydrogen peroxide decomposition and/or reduction. For La0.8Sr0.2MnO3 composite electrodes, along with the catalysis of the chemical decomposition and/or reduction of H2O2 produced on carbon, the perovskite also significantly contributes to the first steps of the ORR. The results of this work suggest that the ORR on the carbon and the oxide components of composite cathodes must be considered as coupled reactions whose contributions cannot be always separated, and that neglecting the contribution of carbon to the ORR electrocatalysis may lead to erroneous values of the catalytic activity of perovskite materials.

Microsized Sn supported by NiTi alloy as a high-performance film anode for Li-ion batteries

A novel Sn–NiTi composite thin film has been prepared by directly co-sputtering a mixture of pure Sn and NiTi shape memory alloy and has been used as an anode for an Li-ion battery for the first time. The thin film has a unique microstructure of microsized Sn particles and microsized Sn grooves uniformly dispersed in an amorphous NiTi (a-NiTi) matrix. The a-NiTi matrix covers the Sn phase and effectively accommodates the volume change resulting from Li–Sn reactions. It also protects the surface of the Sn particles, thus ensuring good cycle performance of the Sn–NiTi composite thin film electrode, with excellent high-rate capability and a low initial irreversible capacity. It delivered a stable capacity of 503 mAh g−1 at 1 C and a high value of 372 mAh g−1 at 15 C, thus demonstrating a significant improvement of the anode performance through the protection of the Sn by the NiTi alloy matrix.

Implementing Realistic Geometry and Measured Diffusion Coefficients into Single Particle Electrode Modeling Based on Experiments with Single LiMn2O4 Spinel Particles

Realistic geometry and diffusion coefficients were measured from a single particle LiMn2O4 electrode and implemented into a three-dimensional multiphysics simulation of a single particle, in order to demonstrate a novel approach to electrode material study. Dispersed particles were used, and electrochemical techniques and atomic force microscopy were performed on isolated single particles. Diffusion coefficients measured from both cyclic voltammetry and the potentiostatic intermittent titration technique ranged between 3.2 × 10−12 and 1.2 × 10−11 cm2/s, which was similar to values measured from thin film LiMn2O4 electrodes. The trend of diffusivity change over potential (versus lithium counter electrode) was similar to those observed from both composite cells and thin film electrodes. The measured diffusion coefficients were then used in simulation of discharge of the irregular particle, by importing the particle morphology into a finite element simulation, in order to simulate intercalation-induced stress generation. Simulation results showed a higher maximum stress generation due to altering diffusivity around the peak current potentials and high local stress concentration on the sharply indented surface area, suggesting that particle irregularities are important in studying both electrochemical performance and local failure mechanisms in cathode materials.

Transparent and flexible electrodes and supercapacitors using polyaniline/single-walled carbon nanotube composite thin films

Large-scale transparent and flexible electronic devices have been pursued for potential applications such as those in touch sensors and display technologies. These applications require that the power source of these devices must also comply with transparent and flexible features. Here we present transparent and flexible supercapacitors assembled from polyaniline (PANI)/single-walled carbon nanotube (SWNT) composite thin film electrodes. The ultrathin, optically homogeneous and transparent, electrically conducting films of the PANI/SWNT composite show a large specific capacitance due to combined double-layer capacitance and pseudo-capacitance mechanisms. A supercapacitor assembled using electrodes with a SWNT density of 10.0 µg cm(-2) and 59 wt% PANI gives a specific capacitance of 55.0 F g(-1) at a current density of 2.6 A g(-1), showing its possibility for transparent and flexible energy storage.

Preparation and Visible Light Photoelectrochemical Response of TiO&lt;sub&gt;2&lt;/sub&gt;-MoO&lt;sub&gt;3&lt;/sub&gt; Composite Nanotube Thin Films

TiO2-MoO3 composite nanotube thin films were obtained by the thermal treatment of titanium dioxide nanotube thin films in the presence of MoO3. Titanium dioxide nanotubes (TiO2 NTs) thin films were prepared by the anodic oxidation of titanium foil. The resultant thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis, and photoelectrochemical methods. The XRD patterns showed that an anatase type TiO2 was present in the thin films. Nanotube structures for the thin films were observed by SEM. MoO3 was dispersed on the TiO2 NT top surface. Elemental analysis by XPS showed that MoO3 recombined with the TiO2 NTs to form TiO2-MoO3 composite nanotube thin films. The influence of time and temperature of thermal treatment on the photoelectrochemical response for the TiO2-MoO3 composite nanotube thin film electrodes were investigated. The photoelectrochemical response of the TiO2-MoO3 composite nanotube thin film increased under visible light illumination compared with the pristine TiO2 NTs. The highest photoelectrochemical response was observed for the TiO2-MoO3 composite nanotube thin film obtained by thermal treatment at 450 °C for 60 min.

Zinc oxide–potassium ferricyanide composite thin film matrix for biosensing applications

Thin film of zinc oxide–potassium ferricyanide (ZnO–KFCN) composite has been deposited on indium tin oxide (ITO) coated corning glass using pulsed laser deposition (PLD). The composite thin film electrode has been exploited for amperometric biosensing in a mediator-free electrolyte. The composite matrix has the advantages of high iso-electric point of ZnO along with enhanced electron communication due to the presence of a redox species in the matrix itself. Glucose oxidase (GOx) has been chosen as the model enzyme for studying the application of the developed matrix to biosensing. The sensing response of the bio-electrode, GOx/ZnO–KFCN/ITO/glass, towards glucose was studied using cylic voltammetry (CV) and photometric assay. The bio-electrode exhibits good linearity from 2.78 mM to 11.11 mM glucose concentration. The low value of Michaelis–Menten constant (1.69 mM) indicates an enhanced affinity of the immobilized enzyme towards its substrate. A quassireversible system is obtained with the composite matrix. The results confirm promising application of the ZnO–KFCN composite matrix for amperometric biosensing applications in a mediator-less electrolyte that could lead to the realization of an integrated lab-on-chip device.

Foam-like, microstructural SnO2–carbon composite thin films synthesized via a polyol-assisted thermal decomposition method

Foam-like, microstructural SnO2-carbon composite thin films were synthesized by refluxing SnCl2.2H2O in ethylene glycol (EG) at 195 degrees C for 4 h under vigorous stirring in air followed by thermal decomposition of the as-synthesized precursor solution, whereby the products were deposited onto stainless steel (SS) substrates. Subsequently, the decomposed product, which now consists only of the microstructural SnO2-carbon composite thin film, without the addition of any binder and carbon black conductive agent, was directly applied as an anode material for use in a Li-ion rechargeable battery. Physical and electrochemical characterizations of the as-synthesized thin films were carried out. The foam-like, microstructural SnO2-carbon composite thin films that undergo thermal decomposition in air at 300 degrees C demonstrated the best cyclability, delivering a specific discharge capacity of approximately 496 mAh g(-1) beyond 100 cycles. We believe that the presence of a uniform, SnO2-carbon network throughout the foam-like thin film, acts not only as an improved conducting network but also buffered the volume expansion upon Li-Sn alloying, resulting in a much improved cycling of the composite thin film electrode.