The growth mechanism and supercapacitor study of anodically deposited amorphous ruthenium oxide films

In the present study, ruthenium oxide (RuO₂) thin films were deposited on the stainless steel (s.s.) substrates by anodic deposition. The nucleation and growth mechanism of electrodeposited RuO₂ film has been studied by cyclic voltammetry (CV) and chronoamperometry (CA). The deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive analysis by X-rays (EDAX) for structural, morphological, and compositional studies. The electrochemical supercapacitor study of ruthenium oxide thin films have been carried out for different film thicknesses in 0.5 M H₂SO₄ electrolyte. The highest specific capacitance was found to be 1190 F/g for 0.376 mg/cm² film thickness.     

Chemical synthesis of nano-porous ruthenium oxide (RuO2) thin films for supercapacitor application

Ruthenium oxide (RuO₂) thin films have been prepared using single step chemical method containing Ru(III) Cl₃ solution in an aqueous medium at low temperature. The structural, morphological and optical properties have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and optical absorption technique. The XRD study revealed the formation of amorphous RuO₂ thin film. The surface examination by SEM showed formation of nano-porous material on the substrate. The TEM study revealed the formation of nanostructured material. The optical absorption studies showed the presence of direct band transition with band gap equal to 2.2 eV. The RuO₂ has proved its applicability in supercapacitor showing 50 F/g specific capacitance in 0.5 M H₂SO₄ at 20 mV/s scan rate.     

Effects of annealing holding time on capacitance performance of RuO2–IrO2–graphene/Ti electrodes

The thermal decomposition method was used to prepare composite electrodes of the Ruthenium oxide–Iridium oxide–Graphene (RuO₂–IrO₂–G). Scanning Electron Microscopy (SEM), X–ray diffraction analysis (XRD), and electrochemical tests were used to study the influence of different annealing holding time on the surface morphology, phase composition, and capacitive performance of the coatings. The results showed that more and more RuO₂, IrO₂ nanoparticles were observed on the surface and cracks of the coating as the annealing holding time increasing. The RuO₂–IrO₂–G/Ti electrode was obtained by annealing for 5 h. The coating of the electrode consists of a certain amount of amorphous phase and nano–crystalline phase, and it had good electronic conductivity and ionic conductivity. At the same time, the electrode was prepared at 5 h had the largest specific capacitance of 778.46 F/g, which increased by 430.89 F/g than the electrode was prepared at 1 h. In addition, the electrode also had superior capacitance performance, capacitance retention and power characteristics.     

Electrodeposition of mesoporous ruthenium oxide using an aqueous mixture of CTAB and SDS as a templating agent

Mesoporous RuO₂ films were electrochemically fabricated on ITO-coated glass substrate from aqueous ruthenium chloride (RuCl₃·nH₂O) solution. To achieve highly stable mesoporous structure, an aqueous mixture of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) was used as a templating agent.The mesoporous structure was confirmed by small angle X-ray diffraction (SAXRD) and transmission electron microscopy (TEM). The addition of small amount (10wt%) of CTAB significantly improved the stability of porous structure. The crystallinity of synthesized RuO₂ thin film was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Specific capacitance of the synthesized films was evaluated by measuring cyclic voltammetry (CV) and charge-discharge curves in 0.5 M H₂SO₄. Compared with non-porous electrode, mesoporous RuO₂ showed higher supercapacitor performance.     

Supercapacitive properties of electrodeposited RuO2 electrode in acrylic gel polymer electrolytes

Hydrous ruthenium oxide (RuO₂) is prepared by electrodeposition on a platinum substrate and its supercapacitive properties are characterized adopting acrylic gel polymer electrolytes, such as poly(acrylic acid) (PAA), potassium polyacrylate (PAAK), and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS). The electrodeposited hydrous RuO₂ exhibits an amorphous compact stratified morphology with a higher loading (0.15 mg cm^?2) than that of a previous report, and shows broad redox peaks on both cathodic and anodic scans in the cyclic voltammetry. In particular, the RuO₂ electrode for supercapacitor adopting the PAMPS electrolyte shows the highest specific capacitance of 642 F g^?1 at 20 mV s^?1. This is due to the efficient utilization of active RuO₂ species and greater proton accommodation toward the negative oxygen sites of PAMPS's side chain. In addition, it is possible to improve sustainability against high-rate current with the RuO₂ electrode with the PAMPS electrolyte, due to the crosslinks of the gel electrolyte, which support the mechanical strength.     

Electrodeposited ruthenium oxide thin films for supercapacitor: Effect of surface treatments

Amorphous and porous ruthenium oxide thin films have been deposited from aqueous Ru(III)Cl₃ solution on stainless steel substrates using electrodeposition method. Cyclic voltammetry study of a film showed a maximum specific capacitance of 650 F g⁻¹ in 0.5 M H₂SO₄ electrolyte. The surface treatments such as air annealing, anodization and ultrasonic weltering affected surface morphology. The supercapacitance of ruthenium oxide electrode is found to be dependent on the surface morphology.     

Superior capacitive characteristics of RuO2 nanorods grown on carbon nanotubes

Carbon nanotubes (CNTs) were used as the electric double layer capacitor (EDLC) material and were synthesized by using thermal chemical vapor deposition (TCVD). To enhance the EDLC capacity, the ruthenium dioxide (RuO₂) nanorods were grown on CNTs by using metal organic chemical vapor deposition (MOCVD). The synthesized CNTs were the principal part and template, and the RuO₂ nanorods were grown outwardly from CNTs. The increase of effective specific area between electrode and electrolyte played an important role in enhancing the capacitance. Different concentrations of KOH were used as electrolyte to measure the capacitance to find the variation of capacitance. Moreover, the RuO₂/CNT composites demonstrated a stable cycle life. The results showed that the RuO₂/CNT composites were a promising supercapacitor device material.     

Electrochemical supercapacitors of electrodeposited PANI/H-RuO2 hybrid nanostructure

Electrodeposited mixed nanostructures composed of conducting polyaniline (PANI) and hydrous ruthenium oxide (H-RuO₂) referred as a hybrid nanostructure was synthesized. The surface morphology was investigated from the field-emission scanning electron microscopy digital photoimages. Fibrous network of PANI and spheres of H-RuO₂ were obtained. PANI embedded H-RuO₂ was confirmed from the Raman spectroscopy analysis. Cyclic-voltammetry, used to characterize the electrochemical capacitive properties of hybrid PANI/H-RuO₂ (RP 30) nanostructure, showed a specific capacitance as high as 322 F/g in 0.5 M H₂SO₄ electrolyte. The electrochemical impedance spectroscopy measurement revealed the low equivalent series resistance.     

Preparation of cobalt oxide thin films and its use in supercapacitor application

Present work explored a room temperature, simple and low cost chemical route for the cobalt oxide film onto copper substrate from cobalt chloride (CoCl₂·6H₂O) precursor and characterization for its structural and electrochemical properties for supercapacitor application. The morphology and crystal structure of the film were investigated by scanning electron microscopy and X-ray diffraction techniques, respectively. The electrochemical supercapacitive properties of cobalt oxide film were evaluated using cyclic voltammetry and galvanostatic charge-discharge methods. The film showed maximum specific capacitance of (165 F/g) in 1.0 M aqueous KOH electrolyte at scan rate 10 mV/s.     

Thickness dependent supercapacitor behaviour of sol-gel spin coated nanostructured vanadium pentoxide thin films

Vanadium pentoxide thin films of various thicknesses have been prepared by sol-gel spin coating method on glass and conducting substrates. X-ray diffraction analysis reveals crystalline nature for the 6–12 layered films (170–310?nm). The crystalline films indicate a preferential orientation of the crystallites along the (200) plane. FTIR studies of the V₂O₅ xerogel show the presence of V–O–V and V=?O bond confirming the formation of V₂O_5. The scanning electron microscope images reveal formation of nanostructures in the 6–12 layered films. Optical absorption studies indicate a band gap of 2.2–2.5?eV. Pseudocapacitance behaviour of the V₂O₅ films was studied using cyclic voltammetric technique and impedance analysis. V₂O₅ films of thickness 202?nm (8 layers) exhibit a specific capacitance of 346?F/g at a scan rate of 5?mV/s.     

Synthesis and characterization of ZnCo2O4 nanomaterial for symmetric supercapacitor applications

ZnCo₂O₄ nanomaterial was prepared by co-precipitation method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), and galvanostatic charge–discharge tests at various current densities. It is shown that the crystal structure and surface morphology play an important role in the enhancement of the specific capacitance. The TEM results clearly indicate that the prepared material shows aggregated particles. The particle size powder was about 50 nm, and SEM pictures indicate a porous morphology. The electrochemical behavior of ZnCo₂O₄ was characterized by mixing equal proportion of carbon nanofoam (CNF). From CV, it is concluded that the combination of redox and pseudo-capacitance increases the specific capacitance up to 77 F g⁻¹ at 5 mV s⁻¹ scan rate. The ZnCo₂O₄-based supercapacitor cell has good cyclic stability and high coulombic efficiency.     

Electrochemical synthesis and performance of PANI electrode material for electrochemical capacitor

Polyaniline (PANI) electrode materials doped with sulfuric acid (H₂SO₄) were prepared by cyclic voltammetry (CV) method in different reaction conditions. The structure and morphology of PANI samples were characterized by Fourier transform infrared spectroscopy and scanning electron microscope. The electrochemical properties of PANI samples were studied by CV, galvanostatic charge/discharge, and electrochemical impedance spectroscopy tests. Additionally, the effects of reaction conditions including aniline concentration, voltammetry scan rate, and deposition time on the morphology and properties of PANI samples were investigated in detail. The results showed that the PANI synthesized under the optimal conditions of 0.2 mol?L^?1 aniline, scan rate 20 mV?s^?1, and deposition time 50 min is in the form of nanorods with a cross-linked network structure. It exhibits an outstanding capacitive performance with good cycle stability and high rate performance. Besides, the specific capacitance of PANI is as high as 757 F?g^?1.     

Charge storage performance of lithiated iron phosphate/activated carbon composite as symmetrical electrode for electrochemical capacitor

In this study, a symmetric electrochemical capacitor was fabricated by adopting a lithium iron phosphate (LiFePO₄)-activated carbon (AC) composite as the core electrode material in 1.0 M Na₂SO₃ and 1.0 M Li₂SO₄ aqueous electrolyte solutions. The composite electrodes were prepared via a facile mechanical mixing process. The structural properties of the nanocomposite electrodes were characterised by scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) analysis. The electrochemical performances of the prepared composite electrode were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (CD) and electrochemical impedance spectroscopy (EIS). The experimental results reveal that a maximum specific capacitance of 112.41 F/g was obtained a 40 wt% LiFePO₄ loading on an AC electrode compared with that of a pure AC electrode (76.24 F/g) in 1 M Na₂SO₃. The improvement in the capacitive performance of the 40 wt% LiFePO₄–AC composite electrode is believed to be attributed to the contribution of the synergistic effect of the electric double layer capacitance (EDLC) of the AC electrode and pseudocapacitance via the intercalation/extraction of H⁺, OH⁻, Na⁺ and SO₃²⁻ and Li⁺ ions in LiFePO₄ lattices. In contrast, it appears that the incorporation of LiFePO₄ into AC electrodes does not increase the charge storage capability when Li₂SO₄ is used as the electrolyte. This behaviour can be explained by the fact that the electrolyte system containing SO₄²⁻ only exhibits EDLC in the Fe-based electrodes. Additionally, Li⁺ ions that have lower conductivity and mobility may lead to poorer charge storage capability compared to Na⁺ ions. Overall, the results reveal that the AC composite electrodes with 40 wt% LiFePO₄ loading on a Na₂SO₃ neutral electrolyte exhibit high cycling stability and reversibility and thus display great potential for electrochemical capacitor applications.     

Effect of nanosize titanium oxide on electrochemical characteristics of activated carbon electrodes

Energy-storage composite electrodes were prepared by mixing activated carbons (ACs) modified with nanosize titanium oxide (TiO₂) through ultrasonic vibration in ethanol solution for 30 min. We examined the cyclic voltammetry of the composite electrodes in an aqueous electrolyte, 1 M H₂SO₄. It was found that the specific capacitance of the composite electrodes measured in a range of 0–0.8 V was increased from 100 to 155 F/g compared electrodes comprised of ACs only. This was attributed to a reduction of polarization of the ACs modified by nanosized TiO₂.     

Electrochemical aspects of sol-gel synthesized MgCoO2 for aqueous supercapacitor and alkaline HER electrocatalyst applications

We report here the cost-effective synthesis of Magnesium Cobalt Oxide (MgCoO₂) sample by the sol-gel synthesis route labeled as MCO - 3. In presence of aqueous 1 M Lithium Sulphate (Li₂SO₄) electrolyte, we obtained a capacitance of 56 F/g, an energy density of 38 Wh/kg and a capacitance retention of 92.53 % (at 5 A/g) after undergoing 1000 charge-discharge cycles. For the aqueous 1 M Sodium Perchlorate (NaClO₄) electrolyte system, we found the capacitance, energy density and capacitance retention of 47 F/g, 31 Wh/kg and 91.41% (at 3.5 A/g for 1000 charge-discharge cycles), respectively. These results establish MgCoO₂ as suitable electrode material in aqueous lithium-ion and sodium-ion supercapacitor devices. Further, MCO - 3 in the presence of aqueous 1 M Potassium Hydroxide (KOH) electrolyte showed an overpotential of 400 mV and a Tafel slope of 174 mV/dec, making it a suitable candidate for alkaline Hydrogen Evolution Reaction (HER) electrocatalyst.     

A nanogravimmetric investigation of the charging processes on ruthenium oxide thin films and their effect on methanol oxidation

The charging processes and methanol oxidation that occur during the oxidation-reduction cycles in a ruthenium oxide thin film electrode (deposited by the sol-gel method on Pt covered quartz crystals) were investigated by using cyclic voltammetry, chronoamperometry and electrochemical quartz crystal nanobalance techniques. The ruthenium oxide rutile phase structure was determined by X-ray diffraction analysis. The results obtained during the charging of rutile ruthenium oxide films indicate that in the anodic sweep the transition from Ru(II) to Ru(VI) occurs followed by proton de-intercalation. In the cathodic sweep, electron injection occurs followed by proton intercalation, leading to Ru(II). The proton intercalation/de-intercalation processes can be inferred from the mass/charge relationship which gives a slope close to 1 g mol⁻¹ (multiplied by the Faraday constant) corresponding to the molar mass of hydrogen. From the chronoamperometric measurements, charge and mass saturation of the RuO₂ thin films was observed (440 ng cm⁻²) during the charging processes, which is related to the total number of active sites in these films. Using the electrochemical quartz crystal nanobalance technique to study the methanol oxidation reaction at these films was possible to demonstrate that bulk oxidation occurs without the formation of strongly adsorbed intermediates such as CO_ads, demonstrating that Pt electrodes modified by ruthenium oxide particles can be promising catalysts for the methanol oxidation as already shown in the literature.     

Electrochemical performance of CeO<Subscript>2</Subscript> nanoparticle-decorated graphene oxide as an electrode material for supercapacitor

Cerium oxide nanoparticles and cerium oxide nanoparticle-decorated graphene oxide (GO) are synthesized via a facile chemical coprecipitation method in the presence of hexadecyltrimethylammonium bromide (CTAB). Nanostructure studies and electrochemical performances of the as-prepared samples were systematically investigated. The crystalline structure and morphology of the nanocomposites were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM), Raman spectrum, and X-ray photoelectron spectroscopy (XPS). Electrochemical properties of the CeO₂ electrode, the GO electrode, and the nanocomposites electrodes were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. The CeO₂ nanoparticle-decorated GO (at the mole ratio of CeO₂/GO = 1:4) electrode exhibited excellent supercapacitive behavior with a high specific capacitance of 382.94 F/g at the current density of 3.0 A/g. These superior electrochemical features demonstrate that the CeO₂ nanoparticle-decorated GO is a promising material for next-generation supercapacitor systems.     

Behavior of Ru surfaces after ozonated water treatment

In order for the development of cleaning technology of extreme ultra violet lithography photomask, the behavior of Ru surfaces after treatment with ozonated deionized water (DIO₃) solution was studied using Ru and ruthenium oxide particles and 2 nm-thick Ru capping layers. No significant changes in crystalline structures or chemical states of the Ru surfaces, nor any similarities with the structures or states of ruthenium oxide, were observed after DIO₃ treatment. Oxidation of ruthenium to form RuO₂ or RuO₃ was not observed. Adsorption of H₂O molecules on the Ru layer increased the surface roughness, but the desorption of H₂O molecules recovered it. Local chemisorption of H₂O molecules on the Ru surface may be the reason why rougher Ru surfaces were observed after DIO₃ cleaning.     

Preparation and characterization of metal-doped carbon aerogel for supercapacitor

Carbon aerogel was prepared by polycondensation of resorcinol and formaldehyde using sodium carbonate as a catalyst with a resorcinol to catalyst ratio of 500. Co-doped carbon aerogels were then prepared by an impregnation method with a variation of cobalt content (1, 3, 5, 7, 10, and 15 wt.%), and their performance for supercapacitor electrode was investigated by measurement of specific capacitance in 1 M H₂SO₄ electrolyte at a scan rate of 10 mV/s. Among the samples prepared, 7 wt.% Co-doped carbon aerogel showed the highest capacitance (100 F/g) and stable cyclability. The enhanced capacitance of Co-doped carbon aerogel was attributed to the faradaic redox reactions of cobalt oxide. On the basis of this result, 7 wt.% Cu-, Fe-, Mn-, and Zn-doped carbon aerogels were also prepared by an impregnation method for use as a supercapacitor electrode. Among the metal-doped carbon aerogels, Mn-doped carbon aerogel showed the highest capacitance (107 F/g) while Cu- and Fe-doped carbon aerogels exhibited the most stable cyclability.     

Li4Mn5O12 prepared using l-lysine as additive and its electrochemical performance

l-Lysine was employed as additive to prepare face-centered cubic spinel Li₄Mn₅O₁₂. During the process, l-lysine played important roles such as complexing agent as well as combusting agent and adjusting the pH values of solution. The physical characteristics of Li₄Mn₅O₁₂ were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical capacitance performance of Li₄Mn₅O₁₂ electrode was characterized by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. These analyses indicated that Li₄Mn₅O₁₂ was able to deliver 168 F?g^?1 within the potential range of 0–1.4 V at a scan rate of 5 mV?s^?1 in 1 mol?L^?1 Li₂SO₄. Nine hundred cycles later, the capacitance faded to 165 F?g^?1 with cutting down by 0.003 F?g^?1 per cycling period and also can remain 98.2 % of original value, displaying a good cycling performance.