mC Cm-2 Research Articles

Morphology Control of Mixed Metallic Organic Framework for High-Performance Hybrid Supercapacitors.

The study presents the binder-free synthesis of mixed metallic organic frameworks (MMOFs) supported on a ternary metal oxide (TMO) core as an innovative three-dimensional (3D)approach to enhance electron transport and mass transfer during the electrochemical charge-discharge process, resulting in high-performance hybrid supercapacitors. The research demonstrates that the choice of organic linkers can be used to tailor the morphology of these MMOFs, thus optimizing their electrochemical efficiency. Specifically, a NiCo-MOF@NiCoO2@Ni electrode, based on terephthalic linkers, exhibits highly ordered porosity and a vast internal surface area, achieving a maximum specific capacity of 2320 mC cm-2, while maintaining excellent rate capability and cycle stability. With these performances, the hybrid supercapacitor (HSC) achieves a maximum specific capacitance of 424.6 mF cm-2 (specific capacity 653.8 mC cm-2) and 30.7 F cm-3 with energy density values of 10.1 mWh cm-3 at 167.4mW cm-3 (139.8 µWh cm-2 at 2310 µW cm-2), which are higher than those of previously reported MMOFs based electrodes. This research introduces a novel approach for metal organic framework based HSCelectrodes, diverging from the traditional emphasis on metal ions, in order to achieve the desired electrochemical performance.

A High Temperature Harvestorer Based on a Photovoltaic Cell and an Oxygen Ion Battery

A High Temperature Harvestorer Based on a Photovoltaic Cell and an Oxygen Ion Battery

Mechanical Exfoliation of Expanded Graphite to Graphene-Based Materials and Modification with Palladium Nanoparticles for Hydrogen Storage.

Hydrogen is a promising green fuel carrier that can replace fossil fuels; however, its storage is still a challenge. Carbon-based materials with metal catalysts have recently been the focus of research for solid-state hydrogen storage due to their efficacy and low cost. Here, we report on the exfoliation of expanded graphite (EG) through high shear mixing and probe tip sonication methods to form graphene-based nanomaterial ShEG and sEG, respectively. The exfoliation processes were optimized based on electrochemical capacitance measurements. The exfoliated EG was further functionalized with palladium nanoparticles (Pd-NP) for solid-state hydrogen storage. The prepared graphene-based nanomaterials (ShEG and sEG) and the nanocomposites (Pd-ShEG and Pd-sEG) were characterized with various traditional techniques (e.g., SEM, TEM, EDX, XPS, Raman, XRD) and the advanced high-resolution pair distribution function (HRPDF) analysis. Electrochemical hydrogen uptake and release (QH) were measured, showing that the sEG decorated with Pd-NP (Pd-sEG, 31.05 mC cm-2) and ShEG with Pd-NP (Pd-ShEG, 24.54 mC cm-2) had a notable improvement over Pd-NP (9.87 mC cm-2) and the composite of Pd-EG (14.7 mC cm-2). QH showed a strong linear relationship with an effective surface area to volume ratio, indicating nanoparticle size as a determining factor for hydrogen uptake and release. This work is a promising step toward the design of the high-performance solid-state hydrogen storage devices through mechanical exfoliation of the substrate EG to control nanoparticle size and dispersion.

Ion-Diode-Like Heterojunction for Improving Electricity Generation from Water Droplets by Capillary Infiltration.

Water-droplet-based electricity generators are emerging hydrovoltaic technologies that harvest energy from water circulation through strong interactions between water and nanomaterials. However, such devices exhibit poor current performance owing to their unclear driving force (evaporation or infiltration) and undesirable reverse diffusion current. Herein, a water-droplet-based hydrovoltaic electricity generator induced by capillary infiltration with an asymmetric structure composed of a diode-like heterojunction formed by negatively and positively charged materials is fabricated. This device can generate current densities of 160 and 450µA cm-2 at room temperature and 65 °C, respectively. The heterojunction achieves a rectification ratio of 12, which effectively suppresses the reverse current caused by concentration differences. This results in an improved charge accumulation of ≈60 mC cm-2 in 1000 s, which is three times the value observed in the control device. When the area of the device is increased to 6 cm2 , the current increases linearly to 1mA, thus demonstrating the scale-up potential of the generator. It has been proven that the streaming potential originates fromcapillary infiltration, and the presence of ion rectification. The proposed method of constructing ion-diode-like structures provides a new strategy for improving generator performance.

Evaluation of Polymer-Coated Carbon Nanotube Flexible Microelectrodes for Biomedical Applications.

The demand for electrically insulated microwires and microfibers in biomedical applications is rapidly increasing. Polymer protective coatings with high electrical resistivity, good chemical resistance, and a long shelf-life are critical to ensure continuous device operation during chronic applications. As soft and flexible electrodes can minimize mechanical mismatch between tissues and electronics, designs based on flexible conductive microfibers, such as carbon nanotube (CNT) fibers, and soft polymer insulation have been proposed. In this study, a continuous dip-coating approach was adopted to insulate meters-long CNT fibers with hydrogenated nitrile butadiene rubber (HNBR), a soft and rubbery insulating polymer. Using this method, 4.8 m long CNT fibers with diameters of 25-66 µm were continuously coated with HNBR without defects or interruptions. The coated CNT fibers were found to be uniform, pinhole free, and biocompatible. Furthermore, the HNBR coating had better high-temperature tolerance than conventional insulating materials. Microelectrodes prepared using the HNBR-coated CNT fibers exhibited stable electrochemical properties, with a specific impedance of 27.0 ± 9.4 MΩ µm2 at 1.0 kHz and a cathodal charge storage capacity of 487.6 ± 49.8 mC cm-2. Thus, the developed electrodes express characteristics that made them suitable for use in implantable medical devices for chronic in vivo applications.

Effect of B-Doping and Manifestation on TiO2-Supported IrO2 for Oxygen Evolution Reaction in Water Electrolysis.

To commercialize hydrogen production by proton exchange membrane (PEM) electrolysis, the amount of rare and precious metal (iridium) required for anodic oxygen evolution reaction (OER) must be greatly reduced. In order to solve the problem, carrier loading is used to reduce the amount of iridium. Unlike the carrier modified by conventional metal element doping, this work doped the carrier with the nonmetallic element and then prepared IrO2/TiBxO2 composite catalyst using the Adams melting method. B-doped TiO2 supports with different doping amounts show the main phase rutile structure. Among them, the conductivity of B-doped carrier shows an increasing trend with the increase of doping amount, because boron can form holes and negative centers after doping, and more carriers improve the conductivity of the support. In addition, since element B is manifested from inside to outside on the support, B can affect the catalytic process. After the manifestation of element B, the carrier loaded with IrO2 exhibited superior electrocatalytic properties. The voltammetric charge per unit mass of 40IrO2/TiB0.3O2#2 (where #2 represents B after manifestation) reaches 1970 mC (cm2 mg)-1, the corresponding overpotential is 273 mV at a current density of 10 mA/cm-2, and the Tafel slope is 61.9 mV/dec Also, the charge transfer resistance is only 15 Ω. Finally, in the stability test, the composite catalyst is also better than pure IrO2 in the 20 000 s operation. Therefore, element B has an unexpectedly positive effect on the catalytic progress on the surface of the support after its manifestation.

Mg-doped NiCoP microflower grown on Ni foam for high-capacity supercapacitor electrode

In this work, a binder-free electrode Mg-doped NiCoP/Ni foam (MNCP-x/NF) was prepared via hydrothermal and phosphorization process, in which echinoid microflower-like MNCP-xwas densely loaded on the NF skeleton. By regulating the Mg2+doping amount, remarkable enhancements in the morphology, mass-loading of MNCP, electrode conductivity and overall electrochemical capacitive properties of MNCP-x/NF have been achieved. Particularly, moderate doped MNCP-0.5/NF exhibits the best energy storage performances with a superior specific capacity (4461 mC cm−2@ 2 mA cm−2), acceptable rate capability (retaining 50.1% @ 50 mA cm−2), and striking cyclability (retaining 83% over 5000 cycles). Moreover, a solid-state asymmetric supercapacitor constructed with MNCP-0.5/NF as cathode, graphene hydrogel/NF (GH/NF) as anode, PVA/KOH gel as electrolyte, outputs the notable energy density of 39.8 Wh kg−1(1.8 mWh cm−3) and power density of 16674 W kg−1(750 mW cm−3), companied by a superior cyclability (retaining 87% over 5000 cycles).

Structural and Magnetic Properties of Electrodeposited Cobalt-Polypyrrole Composite Films

Co particles were electrodeposited at an electrode potential of -2.0 V on ITO/PPy (500 nm) substrates. During Co electrodeposition, charge density was changed from 400 to 5000 mC cm-2 in order to control the Co amount. Current density-time transients showed that the dominant reaction is PPy undoping for the initial times and Co deposition for the later times. Structural characterization was done by a Fourier transformed infrared (FTIR) spectrometer and a scanning electron microscope (SEM). FTIR spectra of the Co-PPy composite films have similar to that of the PPy film but peak intensities decrease as the charge density increases due to the surface covering by Co (by SEM). The chemical composition was detected by an energy dispersive spectrometer. For all films, C and N (belonging to PPy layer), O (due to oxidized character of PPy layer), F (doping anion) and Co peaks were obtained. Magnetic properties were measured by a vibrating sample magnetometer. Some films with Co charge density of 600, 700, 4000 and 5000 mC cm-2 have nearly isotropic magnetic behavior and the others are anisotropic. The isotropic behavior may arise from the very weak texture and preferred orientation of the films.

Eff ects of Film Thickness and Potential on Response and Interference Suppression of Nitrite Biosensor

An amperometric myoglobin-based biosensor was developed for detection of nitrite by entrapping myoglobin (Mb) into an electropolymerized polypyrrole (PPy) fi lm deposited on a platinum (Pt) electrode. In order to optimize the sensor response and minimize the interference caused by a common interfering compound, the effects were investigated of the preparation conditions (fi lm thickness corresponding to an electropolymerization charge of 5–400 mC cm-2) and operating conditions (working potentials of +0.60, +0.65 and +0.70 V) on the response and interference suppression of a nitrite biosensor. The current responses to nitrite and ascorbic acid were examined of the obtained PPy/Mb biosensor. The results showed that as the fi lm thickness increased, the response toward nitrite initially decreased and then slightly increased, while the suppression of interference by ascorbic acid increased. The fi lm thickness substantially affected the interference suppression by ascorbic acid because polypyrrole fi lm possesses a size-exclusion property which can suppress electroactive interferent compounds, such as ascorbic acid, and the size exclusion effect relies considerably on the fi lm thickness. An increase in the diffusion barrier against interference with increased fi lm thickness resulted in the enhanced suppression of ascorbic acid. In addition, the results showed that the working potential had a positive infl uence on the response to nitrite across the range studied. However, all the investigated working potentials had a similar effect on the suppression of ascorbic acid.

Initial Stage of Galvanostatic Li Electrodeposition in PC Electrolyte

Lithium with an atomic number of 3 has a small electrochemical equivalent of 6.9 g per Faraday, and a standard electrode potential of -3.045 V, the lowest among metals. For this reason, batteries using lithium as the anode are lightweight and have a high operating voltage. Li/MnO2 batteries and Li/(CF) n batteries have been commercialized using lithium anode, but they are all primary batteries. Lithium metal anodes are prone to generate dendrite during charging. The key to their practical use as anodes for secondary batteries is whether or not dendrite formation can be suppressed. The success technique of dendrite suppression will be indispensable for not only the realization of liquid electrolyte type battery with high energy density such as Li-S batteries and Li-air batteries but also all solid-state lithium metal battery. Thus, it is urgently required to interdisciplinary accumulate our profound understanding of the lithium metal nucleation and growth phenomena.Since Li metal is conventionally electrodeposited in organic electrolytes because of electrochemical window restriction, Li deposition essentially accompanies the adsorption or decomposition of the organic species on the substrate and deposited Li metal. In galvanostatic or constant current electrolysis, the electrolyte decomposes prior to Li deposition and so-called SEI is formed. Therefore, the nucleation and growth of Li is naturally affected by the existence of SEI layer. Characteristics of SEI strongly influences the charge and/or mass transfer kinetics, which affects the nucleation and growth process followed by the morphological variations. Recent work revealed that Li deposition proceeded underneath SEI(1). Also, TEM observations indicated SEI microstructure(2) and the competitive deposition on tip and root of Li dendrite(3).In this study, constant current electrodeposition of Li was carried out in common organic electrolyte instead of ionic liquid(4) to focus on the effect of current density in the initial stage of the electrodeposition. The electrolyte composed of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and PC. A typical three electrode cell was used in Ar glove box (dew point < -90 ℃), varying current density, salt concentration and temperature. The working electrode was Ni wire 500 μm in diameter (Nilaco Corp.). It was coated with FEP fluoroplastic tube as a sleeve so that the portion in contact with the electrolyte was 10 mm in depth. A lithium foil (200 μm in thickness, Honjo Metal Co., Ltd.) was used as the counter electrode and the reference electrode. The cell was mounted in the temperature-controlled aluminum block. The working electrode was immersed in dimethyl carbonate to rinse the surface and dried in vacuum after electrochemical measurements, followed by XPS and UPS analysis, and SEM observation of deposits.Fig. 1 shows the potential behavior for 0 – 10 mC cm-2 immediately after starting at 0.04 - 60 mA cm-2. In all the current densities, the potential did not immediately jump into the equilibrium potential of Li. The coulomb quantity passing before Li precipitation decreases from 8 to 4 mC cm-2 as the current density increases under the lower current densities of 0.04 - 4 mA cm-2. On the other hand, under the higher current densities of 4 - 60 mA cm-2, it is about 4 mC cm-2 which does not change much with the current density. It is deduced that the SEI formed prior to Li precipitation under constant current conditions shows differences depending on the current density and there may be a transition point around 4 mA cm-2.The typical SEM images of the electrode surface after the electrolysis of 100 mC cm-2 at 0.2 and 8 mA cm-2 are demonstrated in Fig. 2. The appearance is quite different between lower and higher current densities. At 0.2 mA cm-2, both whiskers with several micrometers in length and granular precipitates of 300 - 400 nm in size can be seen. On the other hand, at 8 mA cm-2, no granular shapes are noticed and substantially only whiskers of around 500 nm in length are homogeneously distributed.Li nucleation and growth behaviors will be further examined to focus the effect of not only current density but also salt concentration and temperature. Nucleation & growth behavior of Li electrodeposited in PC electrolyte may be compared with conventional metal electrodeposition researches in aqueous solution system in order to find out any similarity or dissimilarity between both systems.References Jana, R. E. García, Nano Energy, 41, 552–565 (2017).Li, Y. Cui et al., Joule, 2, 2167−2177 (2018).Li, Y. Yu et al., Science, 358, 506–510 (2017).Nishida, K. Nishikawa, M. Rosso and Y. Fukunaka, Electrochim. Acta, 100, 333-341 (2013). Figure 1

A High-Performance Electrode Based on van der Waals Heterostructure for Neural Recording.

Neural electrodes have been widely used to monitor neurological disorders and have a major impact on neuroscience, whereas traditional electrodes are limited to their inherent high impedance, which makes them insensitive to weak signals during recording neural signals. Herein, we developed a neural electrode based on the graphene/Ag van der Waals heterostructure for improving the detection sensitivity and signal-to-noise ratio (SNR). The impedance of the graphene/Ag electrode is reduced to 161.4 ± 13.4 MΩ μm2, while the cathode charge-storage capacity (CSCc) reaches 24.2 ± 1.9 mC cm-2, which is 6.3 and 48.4 times higher than those of the commercial Ag electrodes, respectively. Density functional theory (DFT) results find that the Ag-graphene interface has more doped electronic states, providing faster electron transfer and enhanced interfacial transport. In vivo detection sensitivity and SNR of graphene/Ag electrodes are significantly improved. The current work provides a feasible solution for designing brain electrodes to monitor neural signals more sensitively and accurately.

Transparent, Low-Impedance Inkjet-Printed PEDOT:PSS Microelectrodes for Multi-modal Neuroscience.

Transparent microelectrodes that facilitate simultaneous optical and electrophysiological interfacing are desirable tools for neuroscience. Electrodes made from transparent conductors such as graphene and indium tin oxide (ITO) show promise but are often limited by poor interfacial charge-transfer properties. Here, microelectrodes are demonstrated that take advantage of the transparency and volumetric capacitance of the mixed ion-electron conductor Poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). Ring-shaped microelectrodes are fabricated by inkjet-printing PEDOT:PSS, encapsulating with Parylene-C, and then exposing a contact site that is much smaller than the microelectrode outer diameter. This unique structure allows the encapsulated portion of the microelectrode volume surrounding the contact site to participate in signal transduction, which reduces impedance and enhances charge storage capacity. While using the same 100 μm diameter contact site, increasing the outer diameter of the encapsulated electrode from 300 to 550 μm reduces the impedance from 294±21 to 98±2 kΩ, respectively, at 1 Hz. Similarly, the charge storage capacity is enhanced from 6 to 21 mC cm-2. The PEDOT:PSS microelectrodes provide a low-haze, high-transmittance optical interface, demonstrating their suitability for optical neuroscience applications. They remain functional after a million 1 V stimulation cycles, up to 600 μA of stimulation current, and more than 1000 mechanical bending cycles.

Solvent dielectric effect on electrochemical properties of 3,4-propylenedioxythiophene

The present study is focused on the electrochemical properties of poly(3,4-propylene­dioxy­thiophene) (Poly(ProDOT)), electrocoated on the single carbon-fiber microelectrode (SCFME) in different electrolytic media, with different solvent dielectric constants (35.9, 41.7, 47.5, 53.3, 59.1 and 64.9). The highest deposition charge density of 24.49 mC cm-2 and the highest specific capacitance of 23.17 mF cm-2 were obtained for Poly(ProDOT) synthesized in a medium with the lowest solvent dielectric constant (e = 35.9). Electrochemical impedance spectroscopy (EIS) results of Poly(ProDOT) coated SCFME measured at open circuit potential showed continuously increased impedance magnitudes as ε was increased from 35.9 to 59.1. For all films, almost capacitive impedance responses at lower frequencies at least were obtained. The highest capacitance was observed for the polymer film synthesized in the medium of e = 35.9. The impedance of this film was also measured in different solvent mixtures with different dielectric constants at open circuit potential.

Urchin-like porous NiCo2O4 nanostructure: Morphology control using porous reduced graphene oxide nanosheets for high performance flexible transparent energy storage devices

In this work, the incorporation of porous reduced graphene oxide (RGO) as support for nickel cobaltite and its strong influence on a structural directing agent is studied. It was found in experimental results that the RGO nanosheets, especially the porous carbon network would be favorable to serve as the nucleation sites for the growth of NiCo2O4 nanorods. Importantly, the epoxy groups present in the porous RGO attract an aggregated NiCo2O4 nanoparticle to form aggregated nanorod-like morphology through dangling bonds. The specific capacity of the NiCo2O4/RGO hybrid (606.6 C g-1 at 1 A g-1) is two times superior than that of NiCo2O4 (282.6 C g-1) and the high-rate performance for NiCo2O4/RGO hybrid is 3.5 times better than that of NiCo2O4. An asymmetric supercapacitor constructed with NiCo2O4/RGO (positive electrode) and activate carbon (negative electrode) delivered a maximum energy density of 49.6 W h kg-1 and long cycle life. In addition, a flexible transparent supercapacitor device assembled with the NiCo2O4/RGO hybrid electrode achieved a large areal capacity (5.27 mC cm-2 at 75.5% transparency), high energy density (1.17 mW h cm-2) and outstanding mechanical flexibility.

Molybdenum doping effect on sol-gel Nb2O5:Li+ thin films: Investigation of structural, optical and electrochromic properties

Niobium pentoxide (Nb2O5) has attracted interest in the field of electrochromic devices because of its thermodynamic and chemical stability. However, its performance can be improved by doping with other transition metals or lithium salts, which leads to a change in its crystalline structure and properties. This work describes a study of the influence of molybdenum (Mo) doping on thin films of Nb2O5:Li+ properties. It was observed that the Mo dopant enhanced the cycling stability and reversibility of Nb2O5:Li+ films. The X-ray diffraction (XRD) pointed that the incorporation of the dopant leads to the mixture of the crystalline phases, monoclinic LiNb3O8 and orthorhombic T-Nb2O5. The addition of 7.5 mol% of Mo increased the charge density to 24.5 mC cm-2, ionic conductivity to 1.95 × 10-7 S cm-1, and the reversibility to 95% after 50 color/bleaching cycles. The color change at 500 nm was from 84 to 34%, and the scanning electronic microscopy (SEM) revealed homogeneous and mostly flat surface. The atomic force microscopy (AFM) showed the samples’ surface roughness rising from 0.49 for undoped to 1.15 nm for 7.5 mol% Mo doped film. All collected results suggest that doping improved the performance of Nb2O5:Li+ thin films over cycles, an important property for application in electrochromic devices.

Constructing a hierarchically structured KNi0.67Co0.33PO4·H2O-graphene hydrogel/Ni foam electrode for superior all-solid-state supercapacitor.

A monolithic supercapacitor electrode of a KNi0.67Co0.33PO4·H2O-graphene composite hydrogel supported on Ni foam (KNCP-GH/NF) is first prepared by a one-step hydrothermal method, which achieves notable improvements in the electrode surface area and mass-loading of active materials. The KNCP-GH/NF electrode enjoys a hierarchical open-porous structure, where the KNCP-GH composite hydrogel fills in the voids in NF and the porous graphene hydrogel (GH) simultaneously provides a large support surface for growing active KNCP nanoflowers. Accordingly, the KNCP-GH/NF electrode exhibits a strikingly high capacity of 3240 mC cm-2 (876 C g-1) at 2 mA cm-2 and a satisfactory rate performance with 78.3% retention at 100 mA cm-2. Further, an all-solid-state asymmetric supercapacitor, constituted by using KNCP-GH/NF and Fe2P/GH/NF as the cathode and anode, respectively, and PVA-KOH as the solid-state gel electrolyte, delivers a high energy density of 69.2 W h kg-1 (3.9 mW h cm-3) and a power density of 13 229 W kg-1 (720 mW h cm-3) as well as notable cyclability with 81.2% capacity retention after 10 000 charge/discharge cycles. These attractive performances suggest a promising potential for a hierarchically structured KNCP-GH/NF electrode for the high-performance energy storage application.

Synergistic Interface-Assisted Electrode-Electrolyte Coupling Toward Advanced Charge Storage.

Owing to the limited charge storage capability of transitional metal oxides in aqueous electrolytes, the use of redox electrolytes (RE) represents a promising strategy to further increase the energy density of aqueous batteries or pseudocapacitors. The usual coupling of an electrode and an RE possesses weak electrode/RE interaction and weak adsorption of redox moieties on the electrode, resulting in a low capacity contribution and fast self-discharge. In this work, Fe(CN)6 4- groups are grafted on the surface of Co3 O4 electrode via formation of CoN bonds, creating a synergistic interface between the electrode and the RE. With such an interface, the coupled Co3 O4 -RE system exhibits greatly enhanced charge storage from both Co3 O4 and RE, delivering a large reversible capacity of ≈1000 mC cm-2 together with greatly reduced self-discharge. The significantly improved electrochemical activity of Co3 O4 can be attributed to the tuned work function via charge injection from Fe(CN)6 4- , while the greatly enhanced adsorption of K3 Fe(CN)6 molecules is achieved by the interface induced dipole-dipole interaction on the liquid side. Furthermore, this enhanced electrode-electrolyte coupling is also applicable in the NiO-RE system, demonstrating that the synergistic interface design can be a general strategy to integrate electrode and electrolyte for high-performance energy storage devices.

Sputtered ruthenium oxide coatings for neural stimulation and recording electrodes.

We have investigated the deposition and electrochemical properties of sputtered ruthenium oxide coatings for neural stimulation and recording electrodes. A combination of oxygen and water vapor was used as a reactive gas mixture during DC magnetron sputtering from a ruthenium metal target. The sputtering plasma was monitored by optical emission spectroscopy to determine the reactive species present and confirm the control of plasma chemistry by reactive gas flow rates into the deposition chamber. The effect of the O2 :H2 O gas ratio on the microstructure and electrochemical properties of the ruthenium oxide were studied in detail. We employed a combination of surface characterization techniques, including scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy, to understand the relationship between plasma chemistry and the microstructure of the films produced under different gas flow conditions. Electrochemical characterization included cyclic voltammetry, electrochemical impedance spectroscopy, and voltage transient measurements, performed on planar ruthenium oxide electrodes with a geometric surface area of 1960 μm2 . At an O2 :H2 O gas flow rate ratio of 1:3, a cathodal charge-storage capacity per unit film thickness of 228.7 mC cm-2 μm-1 (median, Q1 = 134.5, Q3 = 236.6, n = 15) and a charge-injection capacity (0.6 V anodal interpulse bias) of 7.4 mC cm-2 (median, Q1 = 6.9, Q3 = 8.3, n = 15) were obtained in phosphate buffered saline. The charge-injection capacity of ruthenium oxide sputtered with water vapor in the reactive plasma is comparable with sputtered iridium oxide (SIROF) and higher than reported values for porous TiN, a commonly employed high-surface area stimulation electrode coating.

Redox-Active Vertically Aligned Mesoporous Silica Thin Films as Transparent Surfaces for Energy Storage Applications.

Organic-inorganic hybrid membranes, made of a high density of redox active moieties covalently bonded to the internal surfaces of vertically aligned mesoporous silica thin films, are relevant for applications in transparent energy storage devices. This is demonstrated here on the basis of functionalized transparent mesoporous silica thin films prepared on the indium-tin oxide electrode from the combination of an electrochemically induced self-assembly method (to generate azide-functionalized silica) and a copper-catalyzed azide-alkyne click reaction (to derivatize the material with electroactive groups). The very small thickness (105 nm) and the uniformly distributed vertical mesochannels with ultranarrow diameter (2 nm) make the hybrid film a promising substrate that not only achieves a transparency of 82% but also provides large surface area to accommodate a high density of redox active species such as ferrocene. In such rigid and insulating porous membranes, the charge transfer reactions take place through a pure electron-hopping mechanism between adjacent redox sites, which are favored by the ordered and oriented mesostructure containing large amounts of uniformly distributed ferrocene functions in the mesochannels. Their performance results from both high charge transfer rates (electron hopping) and easy mass transport (fast diffusion of counter ions). The most effective system is the ferrocene-functionalized silica film prepared from 40% organosilane, which is able to deliver a capacity of 105 C cm-3 (1.10 mC cm-2) at a current density of 0.4 A cm-3 (with up to 48% capacity retention achieved at a charging time as short as 2.8 s). Such an electrode can be associated to an electrodeposited graphene anode in a solid-state battery-capacitor hybrid device, which can deliver 0.74 mC cm-2 at a potential scan rate of 20 mV s-1. The azide-functionalized mesoporous silica film is actually a versatile platform that can be functionalized with different redox molecules, as shown here for cobaltocenium moieties, which may broaden its application field.

Fast Polymerization of Polydopamine Based on Titanium Dioxide for High-Performance Flexible Electrodes.

Dopamine (DA) and its derivatives are promising for the fabrication of functional films and devices with excellent conductivity and long-term stability; nevertheless its polymerization process is typically prolonged. We have proposed the accelerated deposition process using ultraviolet (UV) irradiation with the existence of nanotitanium dioxide (nano-TiO2) in order to realize the rapid and stable synthesis of polydopamine (PDA) films. The in situ deposition process of nanostructured coatings such as platinum nanowire (PtNW) was also proposed by reducing the time of polymerization process to less than 1 h. It also increased the platinum (Pt) chelating rate with PDA, which was about 12 times faster than the traditional photo-oxidation method. Compared with the electrodes of the same size based on Ti/Pt sputtering, the impedance of the proposed PDA/TiO2/PtNW coated electrode was as low as 0.0968 ± 0.0054 kΩ at 1 kHz (reduction of 99.74%). An extremely high cathodic charge storage capacity (CSCc) up to 234.4 ± 3.16 mC cm-2 was also observed, which was about 106.5 and 1.6 times higher than that of Ti/Pt and PDA/PtNW electrodes, respectively. In addition to that, significant photocurrent polarization responses were presented for PDA/TiO2/PtNW electrodes with a stable current of -136.1 μA, exhibiting excellent charge transfer and UV absorption capacities. This co-deposition method has demonstrated great potential to speed up the polymerization process and enhance the electrical performance for flexible electrodes.