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This paper presents a proposal to use an electrochemical flow-by reactor for hydrogen peroxide electrogeneration using cathodes formed from the incorporation of organic redox catalysts (2-ethylanthraquinone, 2-tert-butylanthraquinone, alizarin, and azobenzene) in the structure of gas diffusion electrodes. These electrodes help circumvent the low solubility of oxygen in aqueous solutions. Organic redox catalysts, which typically contain quinone or azo groups in their structure, were added to the electrode mass in a 10% proportion. The electrodes were used to study the electrogeneration of hydrogen peroxide in situ, in an acid medium (0.1 mol L-1 H2SO4 and 0.1 mol L-1 K2SO4, pH 1), inside an electrochemical flow-by reactor. Comparative analysis among the different catalysts indicated that the best electrode for hydrogen peroxide electrogeneration was the gas diffusion electrode modified with 10% of 2-ethylanthraquinone. With an underflow rate of 200 L h-1, hydrogen peroxide was formed with a maximum yield of 998.12 mg L-1 after 2 h at -2.0 V vs Pt//Ag/AgCl, for which the energy consumption was 11.21 kWh kg-1. The use of the electrochemical flow-by reactor was much more efficient, in that it yielded higher concentrations of hydrogen peroxide with extremely low energy consumption, compared to that obtained when using an electrochemical cell. In addition, for ensuring appropriate usage of the electrodes, optimizing their potential for the maximum generation of hydrogen peroxide, and obtaining the highest efficiency for the reduction of oxygen, a fuzzy algorithm was developed to help support the user’s decision.

Quinones can undergo thermodynamically reversible proton-coupled electron transfer reactions and are being applied as electroactive compounds in aqueous organic batteries. However, the electrochemi...

Energy storage is currently one of the most significant technological challenges globally, and supercapacitor is a prominent candidate over batteries due to its ability for fast charging and long lifetime. Supercapacitors typically use porous carbon as electrodes, because of both the high conductivity and surface area of the material. However, the state-of-the-art porous carbon described in the literature uses toxic chemicals and complex procedures that enhance costs and pollute the environment. Thus, a more sustainable procedure to produce porous carbon is highly desirable. In this context, xerogel-like carbons were prepared by a new, cheap, simple route to polymerization reactions of tannin-formaldehyde in a bio-oil by-product. Using bio-oil in its natural pH allowed a cost reduction and avoided using new reactants to change the reactional medium. Textural properties and electrochemical performances were improved by fast activating the material per 20 min. The non-activated carbon xerogel presented a capacitance of 92 F/g, while the activated one had 132 F/g, given that 77% of the components used are eco-friendly. These results demonstrate that renewable materials may find applications as carbon electrodes for supercapacitors. Overhauling the synthesis route with a different pH or replacing formaldehyde may enhance performance or provide a 100% sustainable carbon electrode.

Sodium fluorophosphates are among the most promising materials for positive electrodes in sodium-ion batteries; however, their low electronic conductivity, kinetics limitations, and structural instability prevent them from reaching their full potential. We obtained sodium vanadium fluorophosphates (NVPF) doped with Ti4+ (NVTPF) and Nb5+ (NVNPF) via an original low-temperature synthesis. It was observed that Ti4+ doping facilitated access to electrode sites and provided higher capacities at high current densities while Nb5+ provided a 91.7% capacity retention from the 20th to 200th cycle, which was over the 80.1% capacity retention of NVPF. Moreover, both NVTPF and NVNPF provided diffusion coefficients in the range of ~10−10 cm2 s−1, which was better than ~10−12 cm2 s−1 of NVPF. Additionally, electrochemical impedance spectroscopy and ex situ X-ray diffraction measurements confirmed that Ti4+ enhanced the electrode kinetics and stabilized its structure through sodiation/desodiation reactions. The results presented in this paper might provide insights and new directions to enhance the electrochemical storage properties of fluorophosphates.

In this work, we propose a novel method for the preparation of polypyrrole (PPy) layers on textile fabrics using a reactive inkjet printing technique with direct freezing of inks under varying temperature up to −16 °C. It was found that the surface resistance of PPy layers on polypropylene (PP) fabric, used as a standard support, linearly decreased from 6335 Ω/sq. to 792 Ω/sq. with the decrease of polymerization temperature from 23 °C to 0 °C. The lowest surface resistance (584 Ω/sq.) of PPy layer was obtained at −12 °C. The spectroscopic studies showed that the degree of the PPy oxidation as well as its conformation is practically independent of the polymerization temperature. Thus, observed tendences in electrical conductivity were assigned to change in PPy layer morphology, as it is significantly influenced by the reaction temperature: the lower the polymerization temperature the smoother the surface of PPy layer. The as-coated PPy layers on PP textile substrates were further assembled as the electrodes in symmetric all-solid-state supercapacitor devices to access their electrochemical performance. The electrochemical results demonstrate that the symmetric supercapacitor device made with the PPy prepared at −12 °C, showed the highest specific capacitance of 72.3 F/g at a current density of 0.6 A/g, and delivers an energy density of 6.12 Wh/kg with a corresponding power density of 139 W/kg.

Electrochemical Paper-based Analytical Devices (ePADs) are an alternative to traditional portable analytical techniques due to features such as low-cost, easy surface modification with different materials, and high sensitivity. A fast and simple method to fabricate enhanced ePADs using pencil-drawing which involves the CO2 laser treatment of the carbon surface deposited on paper is described. The electrochemical performances of the devices were evaluated using cyclic voltammetry (CV) with different redox probes and electrochemical impedance spectroscopy (EIS). The electrochemical results show that a treated surface presents a lower resistance to charge transfer and changes the approach of the probe and the overlap of its orbitals with the electrode. To investigate the effects of the laser treatment process, chemical and structural characteristics were evaluated using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. These results indicated that laser treatment promoted the restoration of carbon–carbon double bonds and removed a thin layer of nanodebris present in commercial pencils, resulting in an improvement of the electrochemical kinetics. As a proof-of-concept, the Pencil-Drawing Electrode (PDE) was used for the detection and quantification of furosemide (FUR) in a sample of synthetic urine, exhibiting a limit of detection (LOD) of 2.4 × 10−7 mol L−1. The percentages of recovery of the FUR added to the samples A and B were 95% and 110%, respectively. The analysis using CO2 laser-treated PDE resulted in a fast, simple, and reliable method for this doping agent.

The Nobel Prize in Chemistry 2019 recognized the importance of Li-ion batteries and the revolution they allowed to happen during the past three decades. They are part of a broader class of electrochemical energy storage devices, which are employed where electrical energy is needed on demand and so, the electrochemical energy is converted into electrical energy as required by the application. This opens a variety of possibilities on the utilization of energy storage devices, beyond the well-known mobile applications, assisting on the decarbonization of energy production and distribution. In this series of reviews in two parts, two main types of energy storage devices will be explored: electrochemical capacitors (part I) and rechargeable batteries (part II). More specifically, we will discuss about the materials used in each type of device, their main role in the energy storage process, their advantages and drawbacks and, especially, strategies to improve their performance. In the present part, electrochemical capacitors will be addressed. Their fundamental difference to batteries is explained considering the process at the electrode/electrolyte surface and the impact in performance. Materials used in electrochemical capacitors, including double layer capacitors and pseudocapacitive materials will be reviewed, highlighting the importance of electrolytes. As an important part of these strategies, synthetic routes for the production of nanoparticles will also be approached (part I).

Sodium-ion batteries are a promising alternative to lithium-ion devices, but the development of proper negative electrode materials is still challenging. Here, the properties of a low-voltage sodium titanate material are evaluated. Sodium titanate nanotubes (NTO) were produced by an alkalyne alkaline hydrothermal treatment with TiO2 and consisted of a hydrated Na1.4H0.6Ti3O7 with a surface area of 128 m2 g−1. NTO electrode kinetics were studied by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic intermittent titration techniques. The (de)intercalation of Na+ ions involved two redox pairs at 0.3/0.5 V and 1.0/1.2 V, associated with the present mixture of nanotubes and nanosheets. Surface processes had a 95% coulombic efficiency and a high contribution even at low scan rates, accounting for 47% of the total capacity at 0.5 mV s−1. Upon Na+ removal, the electronic resistance and the semiconductor capacitance increased. Battery tests performed on Na|NTO half-cells showed a reversible capacity of 90 mA h g−1 at 10 mA g−1 and near 100% coulombic efficiency at current rates ranging from 10 mA g−1 to 10 A g−1. Additionally, NTO presented a good capacity retention of 92% after 170 cycles at 100 mA g−1.

Amorphous carbon black (CB) is a highly reactive material for O2 reduction and widely employed in H2O2 generation. Most studies published have confined their investigation to few electrochemical properties of CB and its morphological and structural characterization. However, an in-depth understanding of CB properties and their effects on oxygen reduction reaction appears to be the key to making significant progress in this field. This paper describes the use of quantum mechanical semi-empirical calculations to obtain structural information and electrochemical impedance spectroscopy to access the electrochemical information of Printex L6 CB (PCL6). It is the first report of its kind in the literature. The semi-empirical results show that PCL6 electrode presents an increase in the number of hotspots due to the presence of large amount of sp2 carbon and functional groups in its composition, which favors O2 adsorption at lower potentials. The equilibrium distance on PCL6 electrode is closer to the distance of a double bond (C O), reinforcing O2 bridge-like adsorption model. Furthermore, PCL6 had proved to be thermodynamically more favourable to O2 adsorption and requires relatively lower energy and potential (shift of 150 mV). PLC6 is found to undergo an activation process, probably associated with O2 adsorption, prior to the beginning of reaction.

This work aims to contribute to the understanding of the degradation phenomena of carbon-supported Pt (Pt/C) catalysts in proton exchange membrane fuel cell cathodes, and two procedures are proposed for increasing their stability. The first is performed by inserting niobium pentoxide, and the second one by inserting tungsten carbide onto the carbon support. Both modified cathode materials are analyzed by physical techniques (X-ray diffraction, energy dispersive X-ray analysis, and identical location transmission electron microscopy, IL-TEM), and electrochemical tests (cyclic voltammetry and rotating disc electrode), and the results are compared with those for a commercial Pt/C electrocatalyst (Etek, wt.20%). Accelerated aging tests are performed with a standard protocol (electrode cycling from 0.6 V to 1.0 V vs. RHE (reversible hydrogen electrode), 3 s at each potential), while the microstructure of each electrocatalyst is monitored by IL-TEM. Two phenomena leading to electrochemical surface area loss are detected: Pt particle growth and the loss of catalyst material, mainly due to the support degradation. By comparing IL-TEM profiles before and after the aging tests, it is noted that both support modifications are effective for reducing Pt nanoparticle growth. However, WC addition also increases the particles corrosion and detachment, so that Nb2O5 addition is more effective for increasing Pt/C stability.

In this paper we present a portable photoelectrochemical system developed with screen-printed carbon electrodes (SPCEs) and a 3 W light-emitting diode (LED). The device with 3D printed structure was applied for detecting lactate on TiO2 nanoparticles modified with [Ni(salen)] polymer film (referred to as TiO2@poly[Ni(salen)]). Electrode coating with the polymer increased the sensitivity of the photoelectrochemical sensor, resulting in a linear range from 0.1 to 20 mmol L−1 with a limit of detection (LOD) of 88 μmol L−1. The sensing system exhibited excellent stability, reproducibility, and selectivity. We also demonstrated by in situ Fourier-transform infrared spectroscopy (FTIR) measurements that carbon dioxide (CO2) is the main product from photoelectrooxidation of lactate on TiO2@poly[Ni(salen)]. The portable system can be employed with any type of modified electrodes to function as photoelectroanalytical (bio)sensors, especially for point-of-care diagnostics.

Bisphenol A (BPA) is a critical endocrine disrupter and estrogenic chemical found in plastics, food, water and specially, in thermal receipt paper, and its frequent monitoring is of great relevance because of the health and environmental concerns. Many electroanalytical methods have been reported for BPA, however the electrode poisoning effects observed for this analyte remains a drawback deserving additional efforts for improving the current methodologies. Here, a practical approach has been devised for routine use, encompassing screen-printed electrodes and a minipotentiostat, but incorporating an innovative design based on superparamagnetic nanoparticles combined with active carbon, an effective absorbing substrate for BPA. By attracting the superparamagnetic nanoparticles with an external, miniature Nd 2 Fe 14 B magnet, it was possible to concentrate the analyte onto the working electrode, thus enhancing and improving the electrochemical signal, while protecting the working electrode against the poisoning effect. The method was successfully applied to the analysis of BPA in real samples, yielding excellent results for this type of electrode, with a detection limit of 2.1 × 10 − 7 mol L − 1 and quantification limit of 6.9 × 10 − 7 mol L − 1 .

Based on the fast consumption and depletion of OH- that generate considerable local pH variations from reference bulk values during anodic processes on platinum, rotating ring-disk electrode (RRDE) studies are expected to contribute in elucidating mechanisms and pH implications on kinetics. As more recently demonstrated by Feliu and co-workers[1] , significant pH variations of up to 1.5 pH units during the voltammetric electro-oxidation of ethanol in alkaline media over platinum, even under hydrodynamic conditions, were detected. Using Ptdisk-Ptring electrodes we investigated glycerol electro-oxidation in alkaline media under both conventional (Figure 1) and oscillatory conditions. All ring currents were corrected by the collection efficiency of the electrode, N, of 25.6%. Importantly, the intrinsic ohmic drop of the system might bring about distortions on the ring currents that must be taken into account in order to rule out the cross-talk of the disk and ring electrodes. Parameters such as ionic strength, distance between working and reference electrodes, and, current magnitudes in the disk require special attention in order to avoid misleading conclusions. The detection of pH variation under voltammetric conditions was done by polarizing the ring electrode at 100mV vs. RHE. The local generation of H+ is seen by the cathodic currents registered at the ring (Fig.1,bottom) whose potential is shifted to lower values due to the well-known pH dependence on the equilibrium potential (Nernstian potential). In oscillatory conditions[2] the situation is rather complicated as many soluble intermediate species are produced at the disk, introducing relevant mass-transport limitations to the oscillatory dynamics being recorded. For example, galvanostatic oxidation of glycerol is only observable in stationary conditions: rotation of the electrode modifies importantly the population of intermediates necessary to sustain oscillations. A systematic study of the effects of rotation speed and of different ring polarizations was conducted. Additionally, the interaction of platinum oxides and glycerol in alkaline media, at open circuit potential, was also followed by collection experiments with the ring polarized at different potentials. The results so far demonstrate particular features for the glycerol system unseen for other model systems, yet to be understood. Acknowledgments: A.A.Z., P.B.P. E.G.M. and H.V. acknowledge São Paulo Research Foundation (FAPESP) and Sao Paulo University Research Office for the scholarships (grants #2013-06205-3 and #2012/07313-1) and financial support (grants #2009/07629-6, #2012/21204-0, and #2013/16930-7). References: [1] M.C. Figueiredo, R.M. Arán-Ais, V. Climent, T. Kallio, J.M. Feliu, ChemElectroChem 2 (2015) 1254. [2] C.P. Oliveira, N. V. Lussari, E. Sitta, H. Varela, Electrochim. Acta 85 (2012) 674. Figure 1 In black: Voltammetric profile at 25mV/s of the system 0.3 M Gly + 0.1 M KOH. Ring currents upon 100mV polarization, in red. Figure 1

Hybrid magnetite/carbon quantum dots (MagNP/C-dots) were prepared and their characterization performed by high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Because of their suitable magnetization and electrochemical properties, they were used as versatile electrode modifiers after magnetically confining onto screen printed carbon electrodes (SPE), with the aid of a miniature external magnet. The reported strategy introduces a convenient procedure for assembling modified electrodes, since the nanoparticles can be easily released by removing the magnet. The non-enzymatic magnetic biosensor showed excellent performance in the determination of NADH at the concentration range 2×10−7 to 5×10−6 mol L−1, exhibiting a sensitivity of 0.15 μmol L−1 and detection limit of 20 nmol L−1. The MagNP/C-dots /SPE sensor was also successfully applied for the determination of NADH in serum samples. The interference of typical biological molecules has also been investigated.

Reactive Blue 19 (RB-19) dye has low fixation efficiency, a long half-life and high toxicity. It is easily loss during the cleaning of textiles and can remain in the environment for long time causing serious environmental problems if not removed. This study reports the degradation of RB-19 by: 1) the electrochemical direct degradation with Boron-Doped Diamond (BDD) electrodes and 2) a combined processes using BDD and Reticulated Vitreous Carbon (RVC) electrodes that generates H2O2. The direct degradation uses different current densities and concentrations. High currents densities, longer electrolysis time and low volumetric flow rates, favour RB-19 degradation removing total colour and 100 % TOC at 5 and 60 min respectively. At 41 mA cm-2 current density and 20 dm3 h-1 volumetric flow rate, the energy consumption to degrade 20 mg dm-3 of RB-19 was 279 kWh kg-1. The TOC removal of RB-19 dye combining BDD and RVC at a current density of 41 mA cm-2 was below 72% during 90 min and the energy consumption increased to 612 kWh kg-1. The higher energy consumption obtained during the combined process suggested that the direct degradation process at low volumetric flow rates is more efficient than the combined process.

New composite based on polypyrrole (PPy) and bismuth oxide (α-Bi2O3) was investigated as supercapacitor electrode. The α-Bi2O3 was obtained by hydrothermal route at 500 ºC for 2 h. Cyclic voltammetry was used to electropolymerize PPy on graphite electrode (GE) or on GE/α-Bi2O3. The X-ray diffraction profile of Bi2O3 revealed the α-Bi2O3 monoclinic structure with space group P21/c.The scanning and transmission electron microscopy images showed that PPy coated α-Bi2O3. Raman spectra showed that PPy inhomogeneously coated α-Bi2O3, but it was still possible to obtain a α-Bi2O3 @PPy core-shell hybrid composite with highly ordered α-Bi2O3 with electronic interaction between the oxide and the polymer chain of the polymer. The GE/α-Bi2O3@PPy composite electrode (type I supercapacitor) displayed a predominantly capacitive profile with low impedance values and good electrochemical stability after 50 charge and discharge cycles. The specific capacitance of α-Bi2O3 @PPy composite was found in the range of 634 to 301 F g-1 to gravimetric current of 3 and 10 A g-1, respectively.

Fused deposition modelling 3D printing of a flexible, conductive, disposable and biodegradable platform using graphene-doped polylactic acid (G-PLA) was demonstrated as an integrated device for sampling and detection of explosives. As a proof-of-concept, traces of 2,4,6-Trinitrotoluene (TNT) impregnated on different surfaces were abrasively sampled using the 3D-printed device and readily assembled in a portable electrochemical cell for rapid square-wave voltammetry scans in the presence of 0.1 mol L–1 HCl electrolyte. Nanogram amounts of TNT sampled from metallic, granite and glove surfaces were detected and quantified using the Faraday equation applied to the voltammetric response of TNT immobilised on the electrode surface. Identification of TNT was possible due to the unique voltammetric behaviour obtained on the G-PLA sensor and efficient sampling due to the rough surface and flexibility of the device. Lead and copper determination by stripping voltammetry was also demonstrated on the same device, highlighting the possibility of detecting gunshot residues. Moreover, we demonstrated that simple mechanical polishing of the 3D-printed surface improved the electrochemical sensing properties of the sensor by exposing graphene nanoribbons within the PLA matrix. Hence, this 3D-printed integrated platform holds promise as a rapid and low-cost approach for on-site crime scene investigations.

A composite material consisting of copper-nanoporous gold (Cu-NPG) structures anchored on a screen-printed electrode (SPE) through a new and straightforward two-step electrodeposition process was characterized and employed as a platform to examine the electrochemical behavior of glucose. Results showed that glucose is electrochemically oxidized at considerably less positive potentials with improved sensitivity at the Cu-NPG/SPE sensor, compared to parallel experiments carried out with NPG/SPE and Au/SPE sensors. Analytical parameters such as sensitivity (659.9 μA μmol−1 L cm−2), selectivity, reproducibility (2.7%), limit of detection (0.13 μmol L−1), and stability demonstrate the suitability of the proposed sensor for continuous glucose monitoring. The NPG/SPE sensor offered excellent performance when detecting physiological concentrations of glucose in complex matrices (synthetic saliva).

A new electrode for the photoelectrochemical removal of 17β-estradiol from water using ruthenium oxide nanoparticles supported on reduced graphene oxide is proposed in this study. The morphology, microstructure and the electrochemical performance of the material were characterized using HRTEM, XRD and Raman spectroscopy. The characterization showed the formation of reduced graphene oxide from a micro-wave assisted hydrothermal method with a particle size of 5.0 nm + 2.4 nm. The electrochemical measurements point to a high performance of the electrode in the presence of a white light source. The hormone removal efficiency in water containing 50 μmol L−1 of 17β-estradiol was evaluated using chronoamperometry at +1.0 V and the process was monitored using liquid chromatography. The reaction is pseudo first order with the removal of 92.2% of 17β-estradiol after 60 min of photoelectrocatalytic treatment.

Time consuming thermal treatments are a common place in the preparation of photocatalysts and their immobilization on substrates. In this work nanolayers of TiO 2 were applied at room temperature on gold surfaces by simply exposing the metal during a minute to an acidic aqueous suspension of P25 TiO 2 (10 g L −1 in 0.1 mol L −1 HCl). Repulverization of the commercial semiconductor by dry grinding in a mortar increased the stability of the suspension and more than doubled the photoelectrocatalytic activity of the TiO 2 nanolayer. While the average TiO 2 particle size in the suspension was of 103 ± 3 nm (obtained by DLS), the less than 100 nm thick TiO 2 nanolayer on the gold surface was dominated by particles with diameters ranging from 20 nm (anatase) to 30 nm (rutile) (observed by SEM, TEM and EDS). Photooxidation experiments with EDTA −an emerging organic pollutant– revealed a linear relationship between the photocurrent and the potential applied to the TiO 2 modified electrode until the saturation photocurrent was attained. For a 1.0 mmol L −1 EDTA solution the integrated saturation photocurrent resulted in a net charge, repeatable from one electrode modification to another, of 38 ± 3C L mol −1 cm −2 (conditions: 100 s irradiation with an UV-LED at 365 nm, 91 mW cm −2 ; 0.5 V vs. Ag/AgCl applied potential). A micrometric TiO 2 layer applied on gold by drop casting enhances this net charge by just 50%. Cyclic voltammograms of the ferrocyanide/ferricyanide redox probe on gold remained undisturbed (in the dark) after the application of the TiO 2 nanolayer, but they became distorted with the drop-cast micrometric layer. The photoactivity of the TiO 2 nanolayer lasts with little decay for many days of photoelectrocatalytic treatment of EDTA. The simple and quick modification process at room temperature can be easily scaled-up to large areas.

A glassy carbon electrode (GCE) modified with carbon Printex 6L (Printex6L/GCE) as a novel sensor is proposed. A morphological study was carried out using scanning electron microscopy, and an electrochemical characterization of the proposed electrode was performed by cyclic voltammetry (CV) using [Fe(CN)6]4− as a redox probe. With the incorporation of the carbon Printex 6L film onto the GCE surface, the [Fe(CN)6]4− analytical signal was substantially increased and the difference between the oxidation and reduction potentials (ΔE p) decreased, a characteristic of the electrocatalytic effect. Furthermore, the use of carbon Printex 6L film resulted in an 84 % increase in the oxidation current and a 123 % increase in the reduction current. Faster charge transfer was observed at the proposed electrode/electrolyte interface during CV when compared with GCE. The Printex6L/GCE was tested for ranitidine (RNT) sensing and showed a decrease in the working potential and an increase in the analytical signal, when compared with GCE, again demonstrating an electrocatalytic effect. Under optimized experimental conditions, the developed square-wave adsorptive anodic stripping voltammetry (SWAdASV) method presented an analytical curve that was linear in RNT concentration range from 1.98 × 10−6 to 2.88 × 10−5 mol L−1 with a detection limit of 2.44 × 10−7 mol L−1. The developed Printex6L/GCE was successfully applied to the determination of RNT concentrations in human body fluid samples (urine and serum).

Electrochemical techniques offer high temporal resolution for studying the dynamics of electroactive species at samples of interest. To monitor fastest concentration changes, a micro- or nanoelectrode is accurately positioned in the vicinity of a sample surface. Using a microelectrode array, it is even possible to investigate several sites simultaneously and to obtain an instantaneous image of local dynamics. However, the spatial resolution is limited by the minimal electrode size required in order to contact the electrodes. To provide a remedy, we introduce the concept of scanning bipolar electrochemical microscopy and the corresponding experimental system. This technique allows precise positioning of a wireless scanning bipolar electrode to convert spatially heterogeneous concentrations of the analyte of interest into an electrochemiluminescence map of the sample reactivity. After elucidating the working principle by recording bipolar line and array scans, a bipolar electrode array is positioned at the site of interest to record an electrochemical image of the localized release of analyte molecules.

We report the development of a simple and powerful capacitive aptasensor for the detection and estimation of human epidermal growth factor receptor 2 (HER2), a biomarker for breast cancer, in undiluted serum. The study involves the incorporation of interdigitated gold electrodes, which were used to prepare the electrochemical platform. A thiol terminated DNA aptamer with affinity for HER2 was used to prepare the bio-recognition layer via self-assembly on interdigitated gold surfaces. Non-specific binding was prevented by blocking free spaces on surface via starting block phosphate buffer saline-tween20 blocker. The sensor was characterized using cyclic voltammetry, electrochemical impedance spectroscopy (EIS), atomic force microscopy and contact angle studies. Non-Faradic EIS measurements were utilized to investigate the sensor performance via monitoring of the changes in capacitance. The aptasensor exhibited logarithmically detection of HER2 from 1 pM to 100 nM in both buffer and undiluted serum with limits of detection lower than 1 pM. The results pave the way to develop other aptamer-based biosensors for protein biomarkers detection in undiluted serum.

Pd1ML/Pt(111) and Pd16ML/Pt(111) electrodes were prepared and studied by cyclic voltammetry in both acidic and alkaline electrolytes. Regardless of the electrolyte pH, hydrogen insertion/disinsertion was observed for the Pd16ML/Pt(111) electrode and absent for the Pd1ML/Pt(111) electrode. In the former case (Pd16ML/Pt(111) electrode), hydrogen insertion/disinsertion proceed at different kinetics in acidic and alkaline media, the kinetics being slower in alkaline versus acidic medium. On the contrary, similar rates of insertion/disinsertion of hydrogen were measured at the two pH values (H/Pd ≈ 0.45), demonstrating that the thermodynamics of hydrogen insertion is not depending on the electrolyte pH.

A critical parameter in the design of EDLCs is the determination of electrochemical stability limits for individual combinations of electrode and electrolyte. Using [EMIm][BF4] as an example we demonstrate that the physical properties of the activated carbon used in the electrodes influence the permissible operating potential of an EDLC, and also that the binder material employed can have further effects. When [EMIm][BF4] electrolyte is coupled with electrodes containing PTFE binder, operating potentials as wide as 3.8 V can be utilised. Due to the differences in response under opposing polarisations, it is necessary to employ an asymmetric mass loading in EDLC cells in order to make full use of the operating window. By balancing the charge in the cell, the differences in stable potential limits and capacitative behaviour can be overcome, however we also found that this balance can be influenced by the rate at which these parameters are determined. Three-electrode measurements show that using an appropriate mass loading ratio results in each electrode operating within their determined stability limits. Stable cycling of a full cell at an operating potential of 3.8 V was demonstrated over 50,000 cycles.

Although various processes for the removal of Reactive Black 5 (RB5) dye from textile wastewater have been studied, the degradation pathway of RB5 on boron-doped diamond (BDD) films has not been elucidated. We here report the efficient electro-oxidation of RB5 in aqueous solution using BDD/Ti electrodes and we propose a degradation route based on intermediates and byproducts identified by high performance liquid chromatography-mass spectrometry. BDD films doped with 5000 or 15,000 ppm of B were grown on Ti plates using the hot filament chemical vapor technique to produce electrodes E1 and E2, respectively. Films were evaluated by scanning electron microscopy, X-ray diffraction and Raman spectroscopy before and after several hours of electrolysis and were shown to be of high quality and stability. Total removal of color from RB5 solution was achieved with either electrode by electrolysis at low current density (50 mA cm−2). Total mineralization of the dye solution could be attained with electrode E2 at an applied current density of 100 mA cm−2. Under these conditions, 91% of the chromatographic area associated with RB5 (monitored at 311 nm) was removed, thereby verifying cleavage of the aromatic rings of the dye. Furthermore decolorization of RB5 followed pseudo zero-order kinetics with both electrodes and the apparent rate constant was higher with electrode E2. The results obtained indicate that BDD/Ti is a promising material for the electro-degradation of RB5 since aromatic rings and chromophoric groups were ruptured during electrolysis to generate aliphatic compounds, such as oxalic acid, that can be easily converted into CO2.

A single-step laser scribing process is used to pattern nanostructured electrodes on paper-based devices. The facile and low-cost technique eliminates the need for chemical reagents or controlled conditions. This process involves the use of a CO2 laser to pyrolyze the surface of the paperboard, producing a conductive porous non-graphitizing carbon material composed of graphene sheets and composites with aluminosilicate nanoparticles. The new electrode material was extensively characterized, and it exhibits high conductivity and an enhanced active/geometric area ratio; it is thus well-suited for electrochemical purposes. As a proof-of-concept, the devices were successfully employed for different analytical applications in the clinical, pharmaceutical, food, and forensic fields. The scalable and green fabrication method associated with the features of the new material is highly promising for the development of portable electrochemical devices.

An electrochemical study of the carbamate pesticide pirimicarb (PMC), which acts on the central nervous system, was performed using a boron-doped diamond working electrode. Cyclic, differential pulse, and square-wave voltammetry experiments across a wide pH range (2.0 to 8.0) showed three irreversible oxidation processes in the voltammetric behavior of PMC. The two first processes were pH-dependent, while the third was not. The three oxidation process were independent of each other, and each involved the transfer of one electron. A reaction proposal for the electrochemical oxidation of PMC is shown, and it is supported by mass spectrometry experiments. After this, an analytical method for PMC quantification in water samples by differential pulse (DP) voltammetry is proposed. The optimal DP voltammetric parameters (step potential, amplitude potential, and scan rate) were optimized using experimental design, and an analytical curve was obtained from 2.0 to 219 μmol L−1 with an estimated detection limit of 1.24 μmol L−1. The accuracy of the proposed method was evaluated by the addition and recovery method, with recoveries ranging from 88.6 to 96.3%. Some highlights of the proposed analytical method are its simplicity, reliability, and portability.

An EC-CE-C4D flow system was applied to the investigation of electrocatalytic processes by monitoring carboxylic acids formed during the electro-oxidation at various potentials of primary alcohols (mixture of 1 mmol L−1 of ethanol, n-propanol, n-butanol and n-pentanol) in acidic, neutral and alkaline media. The electro-oxidation was carried out on gold and platinum disk electrodes (3 mm of diameter) in a thin-layer electrochemical flow cell. Products were sampled 50 μm apart from the electrode directly into the capillary. All the generated carboxylates were determined in near real time (less than 2 min) by CE-C4D in counter-flow mode, with Tris/HCl buffer solution (pH 8.6) as BGE. Long sequences of 5 min experiments were run automatically, exploring the applied potential, electrolysis time and solution composition. Electro-oxidation at 1.5 V (vs. Ag/AgCl quasi-reference) during 50 s in acidic medium was found appropriate for both Pt and Au electrodes when the determination of alcohols after derivatization is intended. A noteworthy selectivity effect was observed on the Au electrode. The signal corresponding to pentanoate is similar on both electrodes while the signal of ethanoate (acetate) is four times larger on gold than on platinum. The carboxylate signals were lower in alkaline medium (below the determination limit on Pt) than in acidic and neutral media. On gold, the formation of carboxylates was anticipated (0.85 V in alkaline medium vs. 1.40 V in neutral medium). The automatic online monitoring of electrochemical processes by EC-CE-C4D holds great potential to investigate ionic/ionizable intermediates/products of new electrocatalysts and/or alternative fuels. This article is protected by copyright. All rights reserved

Gold electrodes were easily modified using MPA (3- mercaptopropionic acid) to produce a self assemble monolayer, SAM, in which electrochemically active cysteine molecules were anchored to produce Au/MPA and Au/MPA/CSH electrodes. The functional groups, present on the modified electrode surfaces, were identified using cyclic voltammetry and ferricyanide ions, an electrochemical probe, at variable pH values. The steps which describe the global electrode process were identified and characterized using cyclic voltammetry. It involves the deprotonation of the R-SH superficial groups; production of R-S free radicals from R-S- electrochemical oxidation and attack and of R-S free radicals to the RSH adjacent molecules on the electrode surface, followed by the second electrochemical oxidation step to produce RSSR. The Au/MPA/CSH electrode showed electrocatalytic activity toward oxidation of quercetin in the range of 0.50 to 12.2 μmolL −1 with a detection limit of 0.15 μmolL −1 .

In this work, a reactive inkjet printing (RIP) has been proposed as an useful method for the deposition of reduced graphene oxide (RGO) layers on different textile fabrics - polyacrylonitrile, poly(ethylene terephthalate), and polypropylene. Under the RIP process, the RGO layers were grown on fabrics by printing of graphene oxide (GO) suspension and simultaneously reduced by L-ascorbic acid. This strategy is a simple and one step process to grow conductive layers of RGO on textile substrates at large scale without any post treatment and does not require any corrosive reagent during the process. Thus, obtained binder-free RGO on textile fabrics can be readily used directly as an electrode material. The applicability of the selected textile fabrics modified by RIP deposition of RGO for energy storage application was tested. For this, a flexible all-solid-state supercapacitor was constructed using two RGO coated textile fabrics as electrodes separated by gel electrolyte (poly(vinyl alcohol)/H3PO4 electrolyte). The as-obtained supercapacitor exhibited an area specific capacitance of 13.3 m F/cm2 (79.9 F/g) at a current density of 0.1 mA/cm2, and delivered an energy density of 1.18 mW h/cm2 and the power density of 4.6 mW/cm2.

High performance electrochromic electrodes prepared by the electrophoretic deposition of Au@PEDOT (gold@poly (3,4-ethylenedioxythiophene)) nanoparticles were characterized. A detailed study was performed using scanning transmission electron microscopy (STEM) combined with a chemical analysis at the nanometer level showing core–shell structures with sizes ranging from 2 to 8 nm. X-ray diffraction and Raman experiments were also performed. The modified electrodes present homogeneous surfaces with increased roughness, leading to excellent electrochromic properties like a high chromatic contrast with an electrochromic efficiency of ca. 300 C −1 cm 2 with a response time of approximately 60–70 ms for 90% of coloration. The fast switching was related to the location of the solid state electrochromic reaction, the very thin PEDOT layer surrounding the Au core of the nanoparticles.

A binuclear cobalt complex, [Co2BPP], derived from the (R,R)-Trost-bis-ProPhenol (BPP) ligand, has been investigated as a catalyst for CO2 uptake and its electrochemical reduction. The complex exhibits labile acetate ligands that can be readily exchanged with CO2, leading to pronounced changes in its vibrational spectra, with νC=O peaks observed at 1700 and 1596 cm–1. The electrochemical reduction of the CoIII centers at –0.5 V was significantly enhanced in the presence of CO2, evidencing a chemical reaction coupled to an electrode process. Instead of yielding CO or HCOOH as observed in most artificial systems, formaldehyde was identified as the major product below –1.0 V, showing that CO2 can undergo four-electron reduction by the [Co2BPP] electrocatalyst.

A sensitive way to determine levofloxacin using a sensor based on vertical aligned carbon nanotubes is described. The morphology and the electrochemical performance of the electrodes were characterised by atomic force microscopy, cyclic voltammetry and square wave voltammetry. A scan-rate study and electrochemical impedance spectroscopy showed that the levofloxacin oxidation product is adsorbed on the electrode surface. Differential pulse voltammetry in phosphate-buffer solution allowed the development of a method to determine levofloxacin levels in the range of 1.0–10.0 µmol L−1, with a detection limit of 75.2 nmol L−1. The proposed sensor was successfully applied in the determination of levofloxacin in urine, and the obtained results were in full agreement with those from the HPLC procedure.

In this work we demonstrated the micromanipulation of a single magnetic microparticle (Fe3O4) modified with Prussian blue (PB) for use in magnetic-switchable electrochemistry. A single Fe3O4-PB microparticle with 120 μm was isolated in an electrochemical microcell (20 μL), in which a fine control of PB electrochemical process on carbon electrode (Ø=4.0 mm) was obtained. For cyclic voltammetry, redox processes attributed to PB/PW (Prussian blue/Prussian white) one electron redox couple were observed, however the capacitive currents were very high. On the other hand, by using differential pulse voltammetry, a maximum faradaic current for anodic peak of 200 nA cm−2 at 0.06 V was observed. Several and high stable chronoamperograms were obtained by “switch on” and “switch off” magnetic commutative states for a single microparticle, showing that the system developed here can be very promising for application in electrochemistry. Keywords: Single Fe3O4-PB microparticle, Magnetic-switchable electrochemistry

The ammonia borane (NH3BH3) oxidation reaction (ABOR) was studied on gold electrodes using the rotating disk electrode (RDE) setup and coupled physical techniques: on-line differential electrochemical mass spectrometry (DEMS) and in situ Fourier transform infrared spectroscopy (FTIR). Non-negligible heterogeneous hydrolysis in the low-potential region was asserted via molecular H2 detection. As a consequence, the number of electron exchanged per BH3OH− species is ca. 3 at low potential, and only reaches ca. 6 above 0.6 V vs. RHE. These figures were confirmed by Levich and Koutecki–Levich calculations using the RDE experiments data. The nature of the ABOR intermediates and products was determined using in situ FTIR. While BH2 species were detected during the ABOR, it seems that its adsorption onto the Au electrode proceeds via the O atom, in opposition to what happens during the borohydride oxidation reaction (BOR). Therefore, it is likely that the mechanism of the ABOR differs from that of the BOR. From the whole set of data (RDE, DEMS, FTIR), a relevant reaction pathway was proposed, including competition between the BH3OH− heterogeneous hydrolysis and oxidation at low potential, and preponderant oxidation at higher potential. Finally, a simplified kinetic modeling accounting with this reaction pathway was proposed, which nicely fits the stationary (i vs. E) ABOR plot.

In this study, a novel material for the electrochemical determination of bisphenol A using a nanocomposite based on multi-walled carbon nanotubes modified with antimony nanoparticles has been investigated. The morphology, structure, and electrochemical performance of the nanocomposite electrodes were characterised by field emission gun scanning electron microscopy, energy-dispersive X-ray spectroscopy, and cyclic voltammetry. A scan rate study and electrochemical impedance spectroscopy showed that the bisphenol A oxidation product is adsorbed on nanocomposite electrode surface. Differential pulse voltammetry in phosphate buffer solution at pH 6, allowed the development of a method to determine bisphenol A levels in the range of 0.5–5.0 μmol L−1, with a detection limit of 5.24 nmol L−1 (1.19 μg L−1).

The glycerol electrooxidation reaction (GEOR) has attracted huge interest in the last decade due to the very low price and availability of this polyol. In this work, we studied the GEOR on Pt(111) electrodes by introducing different densities of random defects. Our results showed that the generation of defects on Pt(111) slightly modified the GEOR onset potential, however it generates changes in the voltammetric oxidation charges and also in the relative production of CO2 to carbonyl containing compounds, CO. The voltammetric profiles in the forward scan show two oxidation peaks. FTIR data show that the first one is connected with the GlOH dissociative adsorption to form CO (and others intermediates) while the second one, at higher potentials, matches the onsets of the CO oxidation to CO2 and the CO production. FTIR also confirms that the lower activity of defected electrodes at lower potentials is connected to a higher CO poisoning. DFT calculations show that the presence of CO molecules on a Pt defected surface keeps water and GlOH molecules far from the surface and linked by H bonds. This paper is the last of a series of three works where we explore the GEOR on an important number of different Pt surfaces. These works show that it is difficult to oxidize GlOH at potentials lower than 0.6 V (under our experimental conditions) without suffering an important electrode poisoning (mainly by CO). Since the structure of nanoparticles might be mimicked by defected single crystals, these sets of reports provide a considerable amount of information concerning the influence of such surfaces towards GlOH reaction in acidic media. Therefore, if the well-known "nano"-effect does not produce substantial changes in the activity of Pt materials, they are not useful to be applied in a Direct Glycerol Fuel Cell (DGFC). On the other hand, it is very interesting that the density of electrode defects permits us to tune the relative production of CO2 to CO. Fil: Fernández, Pablo Sebastián. Universidade Estadual de Campinas; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Tereshchuk, Polina. Universidade de Sao Paulo; Brasil Fil: Angelucci, Camilo A.. Universidade Federal do ABC; Brasil Fil: Gomes, Janaina F.. Universidade Federal de São Carlos; Brasil Fil: Garcia, Amanda C.. Universidade de Sao Paulo; Brasil Fil: Martins, Cauê A.. Universidade Federal da Grande Dourados; Brasil Fil: Camara, Giuseppe A.. Universidade Federal do Mato Grosso do Sul; Brasil Fil: Martins, María Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Da Silva, Juarez L. F.. Universidade de Sao Paulo; Brasil Fil: Tremiliosi Filho, Germano. Universidade de Sao Paulo; Brasil

This paper reports the removal of a recalcitrant and toxic dye, Reactive Black 5 (RB-5) by three methods; 1) anodic oxidation (AO) on Boron-Doped Diamond (BDD), 2) by electro-Fenton (EF) process where hydrogen peroxide was produced by oxygen reduction on reticulated vitreous carbon (RVC) electrodes and 3) by the combination of AO–EF. The BDD and RVC electrodes were fitted in a filter-press flow cell in recycle batch mode of operation. The experimental set-up for the AO and EF processes consisted of two electrolyte compartments separated by a Nafion membrane with the dye contained in the anolyte and the catholyte, respectively. The combined AO–EF process used only one electrolyte compartment. The colour and total organic carbon (TOC) removal were more efficient when the AO and EF processes were used separately than the combined process, AO–EF. The influence of current density and initial concentration of ferrous ions were examined. The lowest energy efficiency (208 kWh kg − 1 ) with the EF process was found when − 0.4 V vs. Ag/AgCl was applied to a RVC electrode and the concentration of Fe 2 + was 1.0 × 10 − 4 mol dm − 3 achieving total colour and 74% of TOC removals in less than 90 min electrolysis. All proposed processes were able to promote high percentages of TOC removal following a pseudo-first order kinetic oxidation. The BDD electrode was the most effective material to remove RB-5 dye within 7.5 min and presented the highest apparent rate constant (0.835 min − 1 ) with 82% TOC removal within 30 min at an energy consumption of 291 kWh kg − 1 and 41.1 mA cm − 2 current density. In the case of the combined process AO–EF the electrodegradation rate of RB-5 was at least three times lower, apparent rate constant (0.269 min − 1 ), and 32% of TOC was removed with a high EC (682 kWh kg − 1 ). Therefore oxidation process applied separately was more efficient.

In this study, homemade disposable gold electrodes made from recordable compact disks were modified with carbon nanotubes for amperometric quantification of terbutaline sulfate in pharmaceutical products. A flow cell using an impingent jet of solution on the electrode surface was build and used for amperometric detection, and a series of experiments were carried out to find the best experimental conditions for the new electrode in a specially designed cell. A linear response for terbutaline was obtained in the range from 3.0 × 10(-6) to 5.0 × 10(-4) mol L(-1) (at 0.63 V vs. Ag/AgCl). The limits of detection and quantification were calculated as 5.8 × 10(-7) mol L(-1) (S/N = 3) and 1.9 × 10(-6) mol L(-1) (S/N = 10), respectively. A frequency of 30 injections h(-1) was attained. The proposed method was successfully applied to the analyses of commercial syrup samples, and all results were in good agreement with those obtained by using high performance liquid chromatography and capillary electrophoresis-tandem mass spectrometry.

The borohydride oxidation reaction (BOR) on Pt(111) electrode modified by the electro-deposition of one pseudomorphic Pd layer (Pd1ML/Pt(111)) has been studied in sodium hydroxide solution using cyclic voltammetry in static and dynamic conditions. The results are compared to those obtained at Pt(111) single crystal. Pd1ML/Pt(111) shows an onset potential slightly shifted negative and the BOR current density is overall larger than observed at Pt(111), demonstrating the beneficial influence of the pseudomorphic Pd monolayer towards the BOR. Both surfaces are however very sensitive to surface poisoning by BHx,ad adsorbed intermediates and deactivation by accumulation of hardly-soluble BOR products (BOx species). The forced convection created by rotation of the RDE can nevertheless limit the accumulation of BOR products in the interfacial region, which results in more sustainable BOR performances. Additionally, a modification of the surface signature in sulfuric acid is observed for the two electrodes after BOR, which could suggest that either BOx or BHads species remain and block the electrode surface, or that the surface has been reconstructed/de-structured in the strong reducing environment of BOR experiments.

A novel bio-electrochemical immunosensor for sensitive and selective detection of anti-peptide antibodies of HPV was fabricated by immobilization of a peptide (SPINNTKPHEAR) ( 1 ) linked to a 6-aminohexanoic ( Ahx ) residue and ferrocene (Fc) on a gold electrode surface, used as sensing interface. The Fc– Ahx –peptide (Fc– Ahx –SPINNTKPHEAR) ( 1AFc ) was obtained by solid phase peptide synthesis by using the Fmoc/tBu strategy. Peptides were purified by preparative HPLC, characterized by MS, MALDI-TOF, and Circular Dichroism and their purity was evaluated by using analytical HPLC. The electrochemical behavior of the modified electrode was examined by cyclic voltammetry in phosphate buffer solution (PBS) in order to evaluate the redox behavior of the ferrocene moiety. The influence of anti-peptide antibodies on the voltammetric response of the modified electrode was investigated by comparing results obtained with pre-immune (control) and post immune serum samples at similar dilution factor. Changes in such behavior upon addition of the serum samples to PBS suggested that the fabricated bioelectrochemical sensor was able to recognize the interaction between anti-peptide antibodies and the immobilized peptide ( 1AFc ) with high selectivity and sensitivity. Such influence increased as the dilution decreased, but the effect was less pronounced at relatively high concentrated solutions owing to the effect of the sample matrix. Notwithstanding, the proposed biosensor can clearly detect the target anti-peptide antibodies at a significant large concentration range.

A comparative study was carried out of sonochemical (SCh), electrochemical (ECh) and sonoelectrochemical (SECh) strategies for the degradation of the fungicide thiram in dilute aqueous solution. The SCh and SECh studies were performed using a sonicator equipped with an 11 mm titanium-alloy probe and operated at 20 kHz with a power intensity of 523 W cm(-2). In the ECh and SECh investigations, galvanostatic electrolyses were implemented using a single compartment electrochemical cell with a boron-doped diamond electrode as anode and applied current densities in the range 10-50 mA cm(-2). For these processes, the decrease in concentration of thiram was monitored by high performance liquid chromatographic (HPLC) analysis and values of current efficiency and energy consumption were determined. The results showed that the rate of degradation of thiram and the amount of energy consumed were directly proportional to the applied current density, while current efficiency was inversely related to current density. The kinetics of thiram degradation followed a pseudo first order model with apparent rate constants in the region of 10(-3)min(-1). Thiram in aqueous solution was subjected to "exhaustive" degradation by ECh and SECh processes for 5h at applied current densities of 35 mA cm(-2) and the intermediates/byproducts so-formed were identified by HPLC-mass spectrometry. Mechanisms of the degradation reactions have been proposed on the basis of the results obtained.

A thin-layer electrochemical flow cell coupled to capillary electrophoresis with contactless conductivity detection (EC-CE-C(4)D) was applied for the first time to the derivatization and quantification of neutral species using aliphatic alcohols as model compounds. The simultaneous electrooxidation of four alcohols (ethanol, 1-propanol, 1-butanol, and 1-pentanol) to the corresponding carboxylates was carried out on a platinum working electrode in acid medium. The derivatization step required 1 min at 1.6 V vs. Ag/AgCl under stopped flow conditions, which was preceded by a 10 s activation at 0 V. The solution close to the electrode surface was then hydrodynamically injected into the capillary, and a 2.5 min electrophoretic separation was carried out. The fully automated flow system operated at a frequency of 12 analyses per hour. Simultaneous determination of the four alcohols presented detection limits of about 5 × 10(-5) mol L(-1). As a practical application with a complex matrix, ethanol concentrations were determined in diluted pale lager beer and in nonalcoholic beer. No statistically significant difference was observed between the EC-CE-C(4)D and gas chromatography with flame ionization detection (GC-FID) results for these samples. The derivatization efficiency remained constant over several hours of continuous operation with lager beer samples (n = 40).

Boron-doped diamond (BDD) electrodes have shown characteristics that differ from other conventional electrodes, and that make them an excellent electrode in the electroanalysis, in the electrosynthesis and also in the treatment of wastewater with organic compounds. In this work, two different electrodes doped with (2,000 and 15,000 ppm) were characterized by Raman Spectroscopy and by Scanning electron Microscopy (SEM). In addition, they were characterized electrochemically by cyclic voltammetry. The electroactive area was estimated according to Cottrell's equation before and after the anodic and the cathodic treatment. From the results, it was observed that the electrodes have a similar behavior in the morphology and in the homogeneity of the films. The large potential window was confirmed for both electrodes (2.5 V vs Ag/AgCl) and for the less doped electrode was obtained a larger area without any treatment while for the more doped electrode, the major area was obtained after the cathodic treatment.

The comparison of the efficiencies for boron-doped diamond (BDD) and for DSA-Cl2® type electrodes to degrade the reactive orange 16 (RO16) dye is presented. The results for the dye electrochemical degradation were investigated by spectroscopic techniques UV/VIS analysis, Total Organic Carbon (TOC), and High Performance Liquid Chromatography (HPLC). The BDD electrode showed the higher performance in the whole range of current densities studied for the color removal as well as in the mineralization of organic materials present in such dye.

An easy way to determine norepinephrine (NE) in biological fluid using a platinum ultramicroelectrode array (PtUMEAs) is described. Issues related to UME electrode surface treatment and characterizations are also addressed. At optimized experimental conditions the dynamic concentration range was 1.0 to 10.0 mmol L � 1 with a detection limit of 40.5 nmol L � 1 . The repeatability of current responses for injections of 5 mmol L � 1 NE was evaluated to be 4.0 % (n = 10). This approach obtained excellent sensitivity, a reliable calibration profile and stable electrochemical response for norepinephrine detection. The content of NE in urine samples without any preconcentration, purification, or pretreatment step, was successfully analyzed by the standard addition method using the Pt-UMEAs.

The electrochromic behavior of iron complexes derived from tetra-2-pyridyl-1,4-pyrazine (TPPZ) and a hexacyanoferrate species in polyelectrolytic multilayer adsorbed films is described for the first time. This complex macromolecule was deposited onto indium-tin oxide (ITO) substrates via self-assembly, and the morphology of the modified electrodes was studied using atomic force microscopy (AFM), which indicated that the hybrid film containing the polyelectrolyte multilayer and the iron complex was highly homogeneous and was approximately 50 nm thick. The modified electrodes exhibited excellent electrochromic behavior with both intense and persistent coloration as well as a chromatic contrast of approximately 70%. In addition, this system achieved high electrochromic efficiency (over 70 cm(2) C(-1) at 630 nm) and a response time that could be measured in milliseconds. The electrode was cycled more than 10(3) times, indicating excellent stability.

In this paper we report the electrosynthesis of PVA-protected PtCo films (PVA = poly(vinylalcohol)) and their activities towards the oxygen reduction reaction (ORR). PtCo electrodeposits were potentiostatically obtained in the presence and absence of PVA at distinct potentials. The film morphology and composition were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), which revealed that the use of PVA in the electrodeposition of PtCo films was decisive to achieve better film composition control. Cyclic voltammetry for PVA-protected PtCo films showed that the electrochemical surface area is dependent on the electrodeposition potentials and suggested different adsorption strengths of oxygen-containing species. Films produced in the presence of PVA presented the following activity order towards ORR as a function of the electrodeposition potential ( vs . Ag/AgCl): −0.9 V > −0.8 V > −1.0 V > −0.7 V. In contrast, PtCo films electrodeposited in the absence of PVA displayed very similar activities regardless of the electrodeposition potential. The simplicity of the electrodeposition method combined with its effectiveness enabled the production of “model electrodes” for investigating the fundamental aspects of the reactions taking place in the fuel cell cathodes.

A carbon micro/nanostructured composite based on cup-stacked carbon nanotubes (CSCNTs) grown onto a carbon felt has been found to be an efficient matrix for enzyme immobilization and chemical signal transduction. The obtained CSCNT/felt was modified with a copper hexacyanoferrate/polypyrrole (CuHCNFe/Ppy) hybrid mediator, and the resulting composite electrode was applied to H2O2 detection, achieving a sensitivity of 194 ± 15 μA mmol−1 L. The results showed that the CSCNT/felt matrix significantly increased the sensitivity of CuHCNFe/Ppy-based sensors compared to those prepared on a felt unrecovered by CSCNTs. Our data revealed that the improved sensitivity of the as-prepared CuHCNFe/Ppy–CSCNT/felt composite electrode can be attributed to the electronic interactions taking place among the CuHCNFe nanocrystals, Ppy layer and CSCNTs. In addition, the presence of CSCNTs also seemed to favor the dispersion of CuHCNFe nanocrystals over the Ppy matrix, even though the CSCNTs were buried under the conducting polymer layer. The CSCNT/felt matrix also enabled the preparation of a glucose biosensor whose sensitivity could be tuned as a function of the number of glucose oxidase (GOx) layers deposited through a Layer-by-Layer technique with an sensitivity of 11 ± 2 μA mmol−1 L achieved at 15 poly(diallyldimethylammoniumchloride)/GOx bilayers.