High Electroactive Area Research Articles

A simple process for the deposition of TiO2 onto BDD by electrophoresis and its application to the photoelectrocatalysis of Acid Blue 80 dye

A 4cm2 BDD/TiO2 electrode has been synthesized by a novel method in which nano-particulated TiO2 (P25, Degussa) was electrophoretically deposited onto a boron-doped diamond (BDD) substrate, followed by sintering at 450°C. Its surface characteristics were analyzed by SEM-EDX. The electrocatalytic behavior of the BDD/TiO2 electrode was clarified from the cyclic voltammetry of a 0.50M K4[Fe(CN)₆] solution. The much higher electroactive area of the nano-structured TiO2 deposit over the hybrid electrode gave much higher currents of the Fe(CN)63–/Fe(CN)64– pair than using the raw BDD electrode. When BDD/TiO2 was used in the anodic oxidation of 50mgL−1 Acid Blue 80 solution at pH3.0 and 5.0 at 22.5mAcm−2 in the dark, it decolorized much more rapidly the dye solution compared to anodic oxidation with BDD. This was related to the production of greater amounts of hydroxyl radical at the high electroactive area of the nano-structured TiO2. Quicker color removal was obtained by photoelectrocatalysis by irradiating the BDD/TiO2 anode with a 75mWcm−2 UVA light (λmax=365nm). The dye concentration decay was always much faster than decolorization due to the formation of more recalcitrant colored products from the attack of oxidizing species. In 60min, photoelectrocatalysis removed 96% of Acid Blue 80. The use of nano-structured TiO2 deposited onto BDD as anode in photoelectrocatalysis then exceeds the efficiency of anodic oxidation with the best anode known of BDD.

Chemically versus electrochemically reduced graphene oxide: Improved amperometric and voltammetric sensors of phenolic compounds on higher roughness surfaces

The electrochemistry of hydroquinone (HQ), catechol (CT), and dopamine (DP) on a glassy-carbon electrode (GCE) modified with chemically (CRGO) and electrochemically reduced graphene oxide (ERGO) was investigated and compared for the development of amperometric and voltammetric sensors. Cyclic voltammetric measurements showed higher current on the CRGO-modified GCE, which can be explained by the higher number of sheets compared with ERGO-modified as revealed by SEM images as well as higher roughness surface monitored by AFM, indicating a higher electroactive area. Electrochemical impedance spectroscopy (EIS) revealed that both modified surfaces presented a very similar behavior (Nyquist plots) and lower resistance to electron transfer in comparison with the unmodified GCE. Considering both modified electrodes for sensing purposes, differential-pulse voltammetry (DPV) in unstirred solutions and amperometry under hydrodynamic solutions showed higher sensitivity and lower limit of detection (LOD) values for HQ, CT and DP on the CRGO-modified GCE. These results indicate that the effect of surface rugosity and electroactive area of RGO modified electrodes contribute to the improvement of sensing characteristics of phenolic compounds using either DPV or amperometric detection under flow conditions. DPV and amperometry provided LOD values between 1 and 5nmolL−1 and 12 and 55nmolL−1, respectively, while the latter offers much faster responses resulting in theoretical analytical frequency higher than 1000h−1.

Gold nanoparticles supported on multi-walled carbon nanotubes produced by biphasic modified method and dopamine sensing application

The present work describes the synthesis of a nanocomposite between carbon nanotubes and gold nanoparticles through modified Brust-Schiffin route. Observations by XRD, TEM and TGA techniques showed an uniform, well-distributed and non-agglomerated dispersion of gold nanoparticles (7±4nm of average size) completely loaded onto MWCNTs surface. After further structural characterizations, the nanocomposite was casted onto a glassy carbon electrode and characterized by cyclic voltammetry. A seven-fold density current enhancement was observed, provided by the high superficial electroactive area of the active material. Sensing properties of so-synthesized nanocomposite were tested for dopamine detection in presence of ascorbic and uric acid by square wave voltammetry. After analytical parameters optimization, the dopamine-sensor presented linear range of 4.8×10−7–5.7×10−6molL−1 with detection and quantification limits of 7.1×10−8 and 2.4×10−7molL−1 respectively and high sensitivity. The proposed method was applied in synthetic cerebrospinal fluids samples and the detection of DA in presence of potentially interferences in real samples was performed with satisfactory results.

CuO nanostructures for highly sensitive shape dependent electrocatalytic oxidation of N-acetyl-l-cysteine

The study describes the application of CuO nanostructures as an effective electrode modifying material for the direct electrocatalytic oxidation of N-acetyl-l-cysteine (NAC). The CuO nanostructures were synthesized using hydrothermal growth method with the assistance of NAC, adipic acid (AS) and citric acid (CA) utilized as effective growth modifiers. The morphological characterization of the as-synthesized nanostructures reveled formation of highly distinct and attractive structural features signifying the efficient growth controlling and directing capabilities of the used modifiers. Although, all the fabricated nanostructures were known to possess electrocatalytic potential for the oxidation of NAC. However, the CA modified CuO nanostructures were noted to demonstrate greater sensitivity compared to its other competitors. The developed sensor system relies on the relatively high electro-active area and charged moieties associated with the surface of CA assisted CuO, thus creating a favorable environment for the faster diffusion of analyte towards catalyst surface. The developed sensor exhibited excellent working linearity in the selected concentration range of 0.1 to 5.0μM with estimated LOD value of 0.01μM.

Stable Lithium Metal Anodes for Rechargeable Lithium Metal Batteries

Li metal is an ideal anode material for next-generation energy storage devices due to its extremely high theoretical specific capacity and the lowest negative electrochemical potential [1,2]. However, uncontrolled Li dendrite growth and the side reaction between Li metal and electrolytes have prevented its practical application in rechargeable Li metal batteries. In our contributions, artificial solid electrolyte interphase (SEI) layer and 3D current collector have been developed to address these issues [3,4]. In this presentation, we will introduce an artificial Li3PO4 SEI layer [3] fabricated by in situ reaction of polyphosphoric acid (PPA) with Li metal and its native film (Li2CO3, LiOH, and Li2O). The partial dissolution of the Li native film and formation of the SEI layer lead to a porous structure of the Li surface, thereby promoting Li dendrite formation and growth. In the ingenious design, the native film of Li metal is replaced by the stable and uniform Li3PO4 SEI layer. The artificial Li3PO4 SEI layer with thickness of 50 nm exhibits a smooth surface and a high Young’s modulus (10-11 GPa). Furthermore, the artificial Li3PO4 SEI layer is demonstrated to be stable in the electrolyte and during cycling in a Li|LiFePO4 battery system. The Li-conducting Li3PO4SEI layer can achieve uniform Li deposition, and reduce the side reaction between the Li metal and the electrolyte. Thus, the artificial SEI strategy we described is a promising route to tackle the intrinsic problems of Li metal anodes and other metal based anodes. Furthermore, we will show that Li metal anode can be accommodated in the reserved pores of the 3D current collector [4] with a submicron skeleton and high surface area, thereby suppressing the Li dendrite growth and solving the associated problems of Li metal anodes. Because of the high electroactive area of the submicron 3D structure, the 3D current collector can improve the Li plating/stripping efficiency and reduce the resistance of the Li metal anode. The utilization of the 3D architecture to accommodate the Li metal anode will highlight the importance of rational design of current collectors and reveal a new avenue for developing Li metal anodes with a long lifespan. References Y.-X. Yin, S. Xin, Y.-G. Guo, L.-J. Wan, Angew. Chem. Int. Ed. 2013, 52, 13186.W. Xu, J. L. Wang, F. Ding, X. L. Chen, E. Nasybutin, Y. H. Zhang, J. G. Zhang, Energ. Environ. Sci. 2014, 7, 513.N.-W. Li, Y.-X. Yin, C.-P. Yang, Y.-G. Guo, Adv. Mater. 2015, DOI: 10.1002/adma.201504526.C.-P. Yang, Y.-X. Yin, S.-F. Zhang, N.-W. Li, Y.-G. Guo, Nat. Commun. 2015, 6, 8058

Carbon Supported Noble Metal (Pd and Au) Catalysts Synthesized by an Oxide Route with High Performance for Oxygen Reduction in Acidic Media

Carbon supported palladium (C/Pd) and gold (C/Au) catalysts were synthesized through a synthesis route involving oxide precipitation and partial reduction, and their performance for the oxygen reduction reaction (ORR) in acidic media was studied. Scanning electrochemical microscopy (SECM) ORR screening and tip-generation/substrate collection performed on glassy carbon supported metal spots showed a strong effect of the reactant ratio (precursor salt/precipitant/reducing agent) on the performance of the resulting catalysts for oxygen reduction and hydrogen peroxide production. These SECM results were further confirmed using a rotating ring-disk electrode with Nafion-embedded Vulcan carbon supported dispersed metal nanoparticles, and characterization with XRD and TGA. A significant enhancement in the overall activity for the ORR was observed on both C/Pd and C/Au catalysts under conditions involving metal oxide reduction, compared to those catalysts that were synthesized by direct metal salt reduction. For C/Pd, this enhanced overall activity with concomitant low peroxide yield is due to the different ways in which the metal and unreduced metal oxide in the catalysts interact with the hydrogen peroxide pathway. For C/Au, a highly dispersed metal with high electroactive area is obtained that shifts the potentials for the reduction of oxygen to hydrogen peroxide to near-reversible conditions.

Modified multiwalled carbon nanotube/epoxy amperometric nanocomposite sensors with CuO nanoparticles for electrocatalytic detection of free chlorine

The benefit of using copper (II) oxide nanoparticles (CuO-NPs), which have catalytic activity for the decomposition of hypochlorite solutions, for the amperometric detection of free chlorine is reported. Cyclic voltammetry and electrochemical impedance spectroscopy have been applied for the electrochemical characterization of nanocomposite materials. If the amperometric detection of free chlorine was determined previously using multiwall carbon nanotube (MWCNT) based epoxy nanocomposite sensors, the electrocatalytic reduction of hypochlorite using modified MWCNT/epoxy nanocomposite sensors with CuO-NPs to obtain sensitive devices capable to amperometrically determine traces of free chlorine in water is demonstrated here. The CuO-NPs were incorporated in the nanocomposite electrode in two different ways i) on the MWCNT surface, Route A and ii) in the nanocomposite matrix in powder form, Route B. Both modified-nanocomposite sensors have shown a fast electron transfer exchange, high electroactive area and an enhancement on the electroanalytical signal. Accordingly, a greater sensitivity compared to raw MWCNT/epoxy nanocomposite sensors has been observed, obtaining the lowest limit of detection for the CuO-NPs modified nanocomposite sensors obtained by Route B.

Comparative study of carbon-supported Pd and PdAg catalysts synthesised by the polyol process and reverse micelles methods

Carbon-supported Pd and PdAg nanoparticles were synthesised by the polyol (P) and reverse micelles (RM) methods for use in a comparative study as catalysts for ethanol electro-oxidation in alkaline media. The electrocatalysts were physically and chemically characterised by transmission electron microscopy, X-ray diffraction and thermogravimetric analysis. Electrochemical characterisation was performed by cyclic voltammetry in the absence and presence of ethanol (0.1, 1, 3 M ethanol), chronoamperometry and electrochemical impedance spectroscopy. The electrochemical measurements showed that the catalysts obtained by the RM method presented excellent dispersion and small crystal size, resulting in materials with high electro-active area. However, the PdAg/C catalysts prepared by the polyol process presented better catalytic activity and stability during the electro-oxidation reaction. In addition to the excellent dispersion and low agglomeration promoted by the polyol method, catalytic enhancement can also be associated with the synergic effect between Pd and Ag elements.

Synthesis and Evaluation of Pd/C and PdAg/C Catalysts Prepared by Polyol Process and Reverse Micelles Methods for Ethanol Oxidation Reaction

Carbon-supported Pd and PdAg nanoparticles are synthesized by polyol (P) and reverse micelles (RM) methods to perform a comparative study as catalysts for ethanol electro-oxidation in alkaline media. The aim of present work is to synthesize Pd/C and PdAg/C catalysts by polyol and reverse micelles methods in order to reduce the cost of the electrode anode material and increasing the catalytic activity towards EOR. PdAg/C is evaluated at different ethanol concentrations in alkaline medium. The catalysts were structurally characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Thermo-Gravimetric (TG) analysis. The electrocatalytic performance was studied by Cyclic Voltammetry in absence and presence of ethanol, Chronoamperometry and Electrochemical Impedance Spectroscopy (EIS). Electrochemical measurements showed that the catalysts obtained by reverse micelles presented excellent dispersion and small crystal size, resulting in materials with high electro-active area. However, the PdAg/C catalysts prepared by polyol process presented better catalytic activity and stability during the electro-oxidation reaction (EOR). Besides the excellent dispersion and low agglomeration promoted by using the polyol method, the catalytic enhancement can be also associated to the synergic effect between Pd and Ag elements.

Lightweight, flexible, nanorod electrode with high electrocatalytic activity

We report on a dropcasting method to fabricate lightweight and mechanically flexible electrodes from gold nanorods. The nanorod electrodes possess extremely high electroactive areas, which lead to greatly enhanced electrocatalysis towards oxygen reduction reaction and methanol oxidation reaction when compared to conventional gold disk electrodes.

An Impedance Study of the O 2 | HO 2 − System in Equilibrium on a Gas Diffusion Electrode

The behavior of the redox couple at equilibrium on a commercial uncatalyzed carbon-polytetrafluoroethylene (PTFE) oxygen-diffusion electrode, fed with partial pressures between 0.21 and 1.0 atm, has been studied by electrochemical impedance spectroscopy. Measurements have been made in the open-circuit potential using aqueous solutions with KOH concentrations in the range 1.0-6.0 mol dm−3 and concentrations up 50 mmol dm−3 at 25.0°C. Under these conditions, the system is controlled by activation, the charge-transfer resistance being much higher than ohmic, adsorption, and diffusion resistive elements. The double-layer capacities show that the wetted electroactive areas, much smaller than the total area, depend on the KOH concentration used for activation. True exchange current densities of about 1 μA cm−2 are obtained, while their apparent values are two orders of magnitude greater, since the sluggish reaction is compensated by the high electroactive area. The cathodic process is a first-order reaction with respect to the feed, and independent of and concentrations. For the anodic one, a zero order for and a first order for and are calculated. These results agree with the previously proposed mechanism for the reduction to on the same electrode from voltammetric studies. Indirect evidence on a weak adsorption of is found from the impedance diagrams. © 2002 The Electrochemical Society. All rights reserved.

Voltammetric characterization of an iridium oxide-based system: the pseudocapacitive nature of the Ir 0.3Mn 0.7O 2 electrode

Mixtures of IrO 2+MnO 2 (30:70 mol%) have been electrochemically studied by cyclic voltammetry (CV) in acid solution. The crystalline structure, morphology and the electrochemical properties of the electrodes have been studied as a function of the annealing temperature. X-ray diffraction analysis (XRD), show absence of Mn 2O 3 phase formation and suggest the possible of formation of a solid solution of IrO 2 and MnO 2 mainly between 400 and 450 °C. The voltammetric behavior depends on the potential cycle number and annealing temperature employed in the preparation of the oxide layer. A good potential window in aqueous H 2SO 4 and high electroactive area are obtained due to the contribution of Ir redox transitions. Energy-dispersive X-ray (EDX) and scanning electron microscopy (SEM) analysis suggest an enrichment of the Ir content on the surface at the cost of the dissolution of the manganese present in the film when the electrode is submitted to the continuous potential scan. The electrodes have been found to perform well in electrochemical capacitor applications with a specific capacitance close to 550 F g −1. The large capacitance exhibited by this system arises from a combination of the double-layer capacitance and pseudocapacitance associated with surface redox-type reactions.