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Raman probing of carbon electrode and electrolyte under dynamic conditions is performed here using different aqueous electrolytes to elucidate the fundamental events occurring in electrochemical supercapacitor during charge–discharge processes. The areal capacitance ranges from 1.54 to 2.31 mF cm−2 and it is determined using different techniques. These findings indicate that the Helmholtz capacitance governs the overall charge-storage process instead of the space charge (quantum) capacitance commonly verified for HOPG electrodes in the range of ~ 3 to 7 µF cm−2. Molecular dynamics simulations are employed to elucidate the origin of the reversible Raman spectral changes during the charge–discharge processes. A correlation is verified between the reversible Raman shift and the surface excesses of the different ionic species. A theoretical framework is presented to relate the effect of the applied potential on the Raman shift and its correlation with the surface ionic charge. It is proposed that the Raman shift is governed by the interaction of solvated cations with graphite promoted by polarization conditions. It is the first time that a comparative study on different aqueous electrolyte pH and cation ion size has been performed tracking the Raman spectra change under dynamic polarization conditions and contrasting with comprehensive electrochemistry and dynamic molecular simulations studies. This study shines lights onto the charge-storage mechanism with evidence of Kohn anomaly reduction in the carbon electrode during the reversible adsorption/desorption and insertion/extraction of ionic species.

We report here the activated carbon and cobalt hexacyanoferrate composite, which is applied as the electrode materials in symmetric supercapacitors containing a 1.0 M Na2SO4 aqueous electrolyte. This novel material combines high specific surface area and electrochemical stability of activated carbon with the redox properties of cobalt hexacyanoferrate, resulting in maximum specific capacitance of 329 F g−1 with large voltage working window of 2.0 V. Electrochemical studies indicated that cobalt hexacyanoferrate introduces important pseudocapacitive properties accounting for the overall charge-storage process, especially when I

We report on multi-walled carbon nanotubes (MWCNTs) and an activated carbon (AC) composite material as an electrode for electrical double-layer capacitors (EDLCs). Material flexibility, robustness, and electrical conductivity are features that come from the MWCNTs, while a high specific surface area is an AC's intrinsic property. We prepared different MWCNT : AC ratios in solutions, which were filtered to form a buckypaper. We investigated the specific capacitance, equivalent series resistance, working voltage window (WVW), and the specific energy and power. The best electrochemical findings were obtained for the MWCNT : AC ratio of 1 : 3 with a specific capacitance reaching the theoretical limit. A high working voltage window of 1.4 V was verified in aqueous solution. Simultaneously, the symmetric cells were able to cycle for more than one million cycles in fast charge–discharge galvanostatic tests with 93% capacitance retention. Finally, the main criticism regarding the self-supported electrode materials is the difficulty of welding. In this sense, we presented a particular welding process as proof of concept for electrode scalability. Overall, this novel electrode material exhibits a set of exciting properties, which we now tested in EDLCs.

We report a novel electrode for Li-O2 battery based on radially ordered multi-walled carbon nanotubes functionalized by acid and plasma pre-treatments without degrading its structure with improved wettability leading to more effective active sites. This electrode was used in a device with DMSO/LiClO4 as the electrolyte, presenting good discharge capacity result (2804 mA h g−1C). The defects on the nanotube structure were characterized with RAMAN and a correlation from defects and discharge capacity was observed indicating that the defects could provide larger number of effective regions for discharge products. Raman, FTIR and synchrotron X-ray diffraction characterization over the discharged electrode revealed a large formation of Li2CO3 as the main product, which is uncommon for this system. Further characterization of composition and morphology in time-elapsed discharge also supported a continuous carbonate formation. By limiting the discharge capacity to 500 mA h.g−1C, an improvement in the cycling was observed, however, the higher overpotential needed to decompose the discharge product limited the cell performance.

After a brief presentation of the major aspects involving supercapacitors, their fundamental aspects were reviewed with special emphasis on recent advances accounting for the electric double layer models proposed for porous carbon-based electrodes containing electrochemically active sub-nanometer pores. Despite these important considerations, the main focus of this review is concerned with the major difficulties found in trying to interpret the electrochemical findings obtained for porous electrodes in the presence and absence of a pseudocapacitance (e.g., Faradaic process) due to presence of distributed and dispersion capacitance effects. In this sense, we present a comprehensive analysis concerned with the misuse of the classic electrochemical methods initially proposed for the study of ideally flat and/or spherical electrodes that are commonly adapted to evaluate the specific capacitance exhibited by porous electrodes. We critically discussed the main pitfalls arising from the incorrect interpretation of the electrochemical findings obtained in the time and frequency domains using different electrochemical characterization methods. For the sake of reuniting our better understanding of the electrochemistry of porous electrodes used in supercapacitors, we investigated the most relevant and recent papers in the field. Finally, we highlight some specific electrochemical methodologies proposed for the study of porous electrodes and some guidelines to establish a laboratory protocol to collect the most relevant information about the supercapacitors are presented.

We report here density functional theory calculations and molecular dynamics atomistic simulations to determine the total capacitance of graphene-modified supercapacitors. The contributions of quantum capacitance to the total capacitance for boron-, sulfur-, and fluorine-doped graphene electrodes, as well as vacancy-modified electrodes, were examined. All the doped electrodes presented significant variations in quantum capacitance (ranging from 0 to ∼200 μF cm-2) due to changes in the electronic structure of pristine graphene. The graphene-modified supercapacitors show any appreciable effect on double-layer capacitance being virtually the same for all the devices investigated. The total differential capacitance was found to be limited by the quantum capacitance, and for all the systems, it is lower than the quantum capacitance over the entire voltage window. We found that the total capacitance can be optimized by considering an adequate modification to each electrode in the supercapacitor. In addition, we found that an asymmetric supercapacitor assembled with different doped electrodes, i.e. an F doped negative electrode and an N doped positive electrode, is the best choice for a supercapacitor since this combination results in better capacitance over the entire potential window.

Neutral aqueous electrolytes are known to promote corrosion of carbon coated aluminum current collectors used in electrochemical capacitors, limiting their applications on energy storage devices. Alternatively to the standard electrode manufacturing recipe, we have grown multi-walled carbon nanotubes as the active material on modified aluminum foils to avoid the corrosion of the latter in neutral aqueous solutions. Therefore, the purpose of the present study is the fabrication of a binary alloy that is resistant to corrosion in neutral aqueous solutions. In this sense, we modified standard aluminum foil current collectors by coating them with a thin nickel layer, which was converted on nickel-aluminum alloy (NixAl, x = 1 & x = 3) during the first heating steps of nanotubes growth on the current collector. This novel aluminum modified current collector is electrically conductive and very resistant to corrosion, which allows applying aluminum-based current collectors on aqueous-based electrochemical capacitors devices. To better investigate the electrochemical performance of carbon-based electrodes in aqueous filled coin cell devices, we performed several electrochemical studies using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. Our results show specific electrode capacitance is up to ∼60 F g−1. After 85,000 (re)charge/discharge cycles, the cell operating on 0–1.5 V voltage range, indicate very long lifespan with no significant loss of specific capacitance and energy density. These results are unexpected for aluminum current collectors on supercapacitor or batteries. On the Ragone plot, our aqueous-based electrochemical capacitor is on supercapacitors region with fairly high power and energy densities.

We report an electrode material for supercapacitors composed of nickel oxide (NiO) nanoparticles supported onto radially oriented multi-walled carbon nanotubes (CNTs) using a stainless-steel fine-mesh as the support (AISI:CNT-NiO). CNT scaffolds showed a turbostratic multi-walled structure with an interplanar spacing of 0.32 ± 0.02 nm and a diameter of ∼20–100 nm. NiO nanoparticles exhibited a diameter of ∼2–7 nm. X-ray data confirmed the presence of NiO in the scaffold. A large pseudocapacitive voltage range of 2.0 V was obtained in a 1.0 M Li2SO4 aqueous solution. The main contribution to the overall pseudocapacitance is due to the presence of reversible solid-state surface Faradaic reactions involving the Ni(II)/Ni(III) redox couple. High specific capacitance values of ∼1200 F g−1 at 5 A g−1 for the AISI:CNT-NiO electrode were extracted from galvanostatic discharge curves. Considering the contribution of negative voltages, the specific power and energy determined using cyclic voltammetry exhibited values of ∼140 Wh kg−1 and ∼9 W kg−1, respectively, at 0.02 V s−1. A specific capacitance of ∼1028 F g−1 was obtained at this scan rate. Even after 40,000 cycles carried out under galvanostatic conditions, the symmetric coin cell remained stable with a very high coulombic efficiency of ∼99%, which is a remarkable result. Also, we attributed to carbon nanotubes an extraordinary stability as electron drain on the current collector. The morphology factor analysis revealed that 19% of the electrochemically active surface area is confined to the inner surface regions of the porous nanostructured active layer. A low value of 0.15 mΩ g was extracted for the equivalent series resistance. New insights are presented concerning the true meaning of negative voltages for coin cells. Interesting findings regarding the porous nature of electrodes were elucidated using the impedance technique.

Different nanostructured mixed metal oxide (MMOs) electrodes containing Sn, Ru, and Ir supported on titanium with the nominal composition Ti/[Sn0.5Ru(0.5−x)Ir(x)]O2 were prepared using the drop-coating method. SEM analysis revealed the presence of oxide islands in the microsized domains of ca. 50 μm separated from each other by cracks. On the contrary, analysis of the nanosized domains revealed the presence of nanostructures containing rectangular grains with an average diameter of ca. 200 nm. The discrepancy between the nominal and real oxide compositions was attributed to volatilization of Sn during the heat treatment. XRD analysis revealed a poor degree of crystallinity and an average crystallite size of 15 ± 4 nm. Different electrochemical studies revealed higher specific pseudocapacitances in the range of 175–222 F g−1 for the MMO containing 50 mol% Ir. The low values obtained for the morphology factor (0.11 ≤ φ ≤ 0.33) indicate a relatively narrow interval of 11–33% for the active surface regions confined to the inner surface regions of the oxide layers. The chronoamperometric findings obtained for short times (t ≤ 50 ms) permitted evaluation of the electrical double-layer capacitance (Cedl), with verified maximum values in the range of 68–75 F g−1 for the MMO containing 50 mol% Ir. On the contrary, the experimental findings obtained for long times (0.1 s ≤ t ≤ 3 s) revealed that the reversible solid-state Faradaic reactions did not exhibit a Fickian behavior. The impedance analysis revealed that MMOs exhibit a porous electrode behavior (De Levie’s model) permitting the determination of the pseudocapacitance and the resistance of the electrolyte inside the pores.

Superior electrochemical performance, structural stability, facile integration, and versatility are desirable features of electrochemical energy storage devices. The increasing need for high‐power, high‐energy devices has prompted the investigation of manufacturing technologies that can produce structured battery and supercapacitor electrodes with optimized charge transport. While conventional electrode production techniques are becoming increasingly obsolete and incompatible with technological developments such as wearables and flexible electronics, additive manufacturing (AM) has emerged as one of several state‐of‐the‐art tools to produce 3D‐structured electrodes with morphology control, high yield, and scalability. Herein, a comprehensive review of the major AM technologies and most recent literature about designing and manufacturing electrode materials for batteries and supercapacitors is presented. A thorough discussion of research opportunities and challenges in this promising field is also presented to introduce the potential and importance of AM to current developments involving electrode materials.

It is common to find in the literature different values for the working voltage window (WVW) range for aqueous-based supercapacitors. In many cases, even with the best intentions of the widening the operating voltage window, the measured current using the cyclic voltammetry (CV) technique includes a significant contribution from the irreversible Faradaic reactions involved in the water-splitting process, masked by fast scan rates. Sometimes even using low scan rates is hard to determine precisely the correct WVW of the aqueous-based electrochemical capacitor. In this sense, we discuss here the best practices to determine the WVW for capacitive current in an absence of water splitting using complementary techniques such as CV, chronoamperometry (CA), and the electrochemical impedance spectroscopy (EIS). To accomplish this end, we prepare and present a model system composed of multiwalled carbon nanotubes buckypaper electrodes housed in the symmetric coin cell and soaked with an aqueous-based electrolyte. The system electrochemical characteristics are carefully evaluated during the progressive enlargement of the cell voltage window. The presence of residual Faradaic current is verified in the transients from the CA study, as well as the impedance changes revealed by EIS as a function of the applied voltage, is discussed. We verify that an apparent voltage window of 2.0 V determined using the CV technique is drastically decreased to 1.2 V after a close inspection of the CA findings used to discriminate the presence of a parasitic Faradaic process. Some orientations are presented to instigate the establishment in the literature of some good scientific practices concerned with the reliable characterization of supercapacitors.

A green chemical method is reported for the synthesis and functionalization of high surface area carbon-based materials for applications as electrodes in short-term energy storage devices, such as supercapacitors. The proposed method is focused on sustainable chemistry and engineering. Our results evidenced an excellent performance of electrochemical capacitor devices with a high lifespan over a wide working voltage with low equivalent series resistance. Great enhancement of electrode wettability and charge transfer at the electrode/electrolyte interface using oxygenated surface functional groups was obtained using the present method. Actually, the present findings are quite promising thus encouraging further investigations of this green-functionalization method for all other carbon-based materials, such as graphene, carbon nanotubes, doped-diamond, and so on.

Nowadays it is mandatory sustainable energy production and storage. In this scenario, supercapacitors play an important role as ultrafast energy storage devices with long lifetime and high efficiency features. The new era of these devices is based on new materials and electrolytes that are environment-friendly during manufacturing and applications. This paper presents a high surface area mesoporous Carbon (MC) material direct growth on aluminum current collector on an environment-friendly process. MC material showed specific capacitance of ~ 8 F g− 1 and impressive chemical stability. Prepared with two MC electrodes, low-cost cellulosic separator and aqueous neutral electrolyte, the supercapacitor coin cells presented very low equivalent series resistance, ~ 100% device storage and supply efficiency, then almost no Capacitance, Energy and Power lost after dozen thousand cycles (on the optimized cell). The Ragone plot contrasts our data with conventional capacitors, electric double-layer capacitor (EDLC) and batteries, fitting them well into the EDLC category. For our best understanding, the excellent electric contact of MC and Al current collector is the key parameter to achieve a minimal ESR, higher efficiency and longer lifetime. The detailed characterization of material and devices are presented herein, evidencing MC as promising materials for energy storage applications.

To date is emergent the development of novel coatings to protect erosion, especially to preventive dentistry and restorative dentistry. Here, for the first time we report the effectiveness of multi-walled carbon nanotube/graphene oxide hybrid carbon-base material (MWCNTO-GO) combined with nanohydroxyapatite (nHAp) as a protective coating for dentin erosion. Fourier transform Raman spectroscopy (FT-Raman), scanning electron (SEM), and transmission electron (TEM) microscopy were used to investigated the coatings and the effect of acidulated phosphate fluoride gel (APF) treatment on bovine teeth root dentin before and after erosion. The electrochemical corrosion performance of the coating was evaluated. Raman spectra identified that: (i) the phosphate (ν1PO43-) content of dentin was not significantly affected by the treatments and (ii) the carbonate (ν1CO32-) content in dentin increased when nHAp was used. However, the nHAp/MWCNTO-GO composite exposited lower levels of organic matrix (CH bonds) after erosion compared to other treatments. Interesting, SEM micrographs identified that the nHAp/MWCNTO-GO formed layers after erosive cycling when associate with APF treatment, indicating a possible chemical bond among them. Treatments of root dentin with nHAp, MWCNTO-GO, APF_MWCNTO-GO, and APF_nHAp/MWCNTO-GO increased the carbonate content, carbonate/phosphate ratio, and organic matrix band area after erosion. The potentiodynamic polarization curves and Nyquist plot showed that nHAp, MWCNT-GO and nHAp/MWCNT-GO composites acted as protective agents against corrosion process. Clearly, the nHAp/MWCNTO-GO composite was stable after erosive cycling and a thin and acid-resistant film was formed when associated to APF treatment.

Imipramine (IMP), a tricyclic antidepressant drug, is commonly prescribed for treatment of psychiatric patients suffering from different forms of depression. The appropriate amount of drug intake is crucial to ensure the optimum therapeutic effects minimizing severe collateral effects and toxicity. Therefore, the monitoring of imipramine is essential for its clinical applications. Herein, we report an electrochemical sensor based on a composite of ferrocenecarboxylic acid (FCA), β-cyclodextrin (CD), and oxidized multi-walled carbon nanotubes (f-CNT) modified glassy carbon electrode for detection of IMP at low potential. The electrochemical behavior of the proposed sensor was characterized by scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry. The results show that imipramine determination using the proposed sensor occurs around 0 V vs Ag/AgCl in phosphate buffer pH 7.0. The calibration curves were obtained by cyclic voltammetry and differential pulse voltammetry, with linear ranges of 10 to 350 μmol L−1 and 0.1 to 10 μmol L−1, respectively. A detection limit of 0.03 μmol L−1 was obtained for the detection of IMP. The sensor was applied for IMP determination in psychotropic drugs and urine samples and the results show a recovery percentage between 99 and 101% for the analyte.

An electrochemical sensor based on functionalized multiwalled carbon nanotubes (MWCNTf) has been developed and applied for determination of anticancer drug flutamide in pharmaceutical and artificial urine samples. The electrode was prepared by modifying a glassy carbon electrode with MWCNTf, denoted herein as MWCNTf/GCE. The MWCNTf/GCE electrode exhibited high catalytic activity, high sensitivity, and high stability and was applicable over a wide concentration range for flutamide. The effects of the scan rate, pH, and nature of the electrolyte on the electrochemical behavior of flutamide on the MWCNTf/GCE were investigated. The results showed that this electrode presented the best square-wave voltammetric response to flutamide in Britton–Robinson buffer solution at pH 5.0 at frequency of 50 Hz and amplitude of 0.06 V. The proposed sensor presents a wide linear response range from concentration of 0.1 μmol L−1 up to 1000 μmol L−1 (or 27.6 μg L−1 up to 0.27 g L−1), with limit of detection, limit of quantification, and sensitivity of 0.03 μmol L−1, 0.1 μmol L−1, and 0.30 μA μmol−1 L, respectively. The MWCNTf/GCE electrode was successfully applied for determination of flutamide in pharmaceutical formulations and artificial urine samples, giving results in agreement with those obtained by a comparative method described in literature. A paired Student’s t-test revealed no statistical difference between the reference and proposed method at 95% confidence level. The average recovery for fortified samples was 101 ± 1%.

Electric double-layer capacitors (EDLCs) are energy storage devices that have attracted attention from the scientific community due to their high specific power storage capabilities. The standard method for determining the maximum power (Pmax) of these devices uses the relation Pmax = U2/4RESR, where U stands for the cell voltage and RESR for the equivalent series resistance. Despite the relevance of RESR, one can observe a lack of consensus in the literature regarding the determination of this parameter from the galvanostatic charge-discharge findings. In addition, a literature survey revealed that roughly half of the scientific papers have calculated the RESR values using the electrochemical impedance spectroscopy (EIS) technique, while the other half used the galvanostatic charge discharge (GCD) method. RESR values extracted from EIS at high frequencies (>10 kHz) do not depend on the particular equivalent circuit model. However, the conventional GCD method better resembles the real situation of the device operation, and thus its use is of paramount importance for practical purposes. In the latter case, the voltage drop (ΔU) verified at the charge-discharge transition for a given applied current (I) is used in conjunction with Ohm’s law to obtain the RESR (e.g., RESR = ΔU/ΔI). However, several papers have caused a great confusion in the literature considering only applied current (I). In order to shed light on this important subject, we report in this work a rational analysis regarding the GCD method in order to prove that to obtain reliable RESR values the voltage drop must be normalized by a factor of two (e.g., RESR = ΔU/2I).

We report here on the performance of quasi-solid-state potassium ion electrolyte filling electrochemical supercapacitors. The electrolyte is composed of aqueous-based polyvinyl alcohol with potassium and sulfate ions. This electrolyte is first investigated filling the coin cells with two identical multi-walled carbon nanotube buckypapers as the electrode materials, and later, it was analyzed in a pouch cell. Our electrochemical results, obtained from different techniques, show that the cell's working voltage window is as wide as 1.6 V, yielding a volumetric capacitance of 18 F cm−3, and equivalent series resistance smaller than 2.5 Ω. We prepare a pouch cell with our best coin cell findings to investigate the cell's mechanical behavior. Our findings showed that quasi-solid-state potassium ion-based supercapacitors are highly flexible and robust, thus encouraging further investigation on the development of flexible supercapacitors to be applied on various wearable and bendable devices.

A novel platform for electroanalysis of isoniazid based on graphene-functionalized multi-walled carbon nanotube as support for iron phthalocyanine (FePc/f-MWCNT) has been developed. The FePc/f-MWCNT composite has been dropped on glassy carbon forming FePc/f-MWCNT/GC electrode, which is sensible for isoniazid, decreasing substantially its oxidation potential to +200 mV vs Ag/AgCl. Electrochemical and electroanalytical properties of the FePc/f-MWCNT/GC-modified electrode were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electrochemical microscopy, and amperometry. The sensor presents better performance in 0.1 mol L−1 phosphate buffer at pH 7.4. Under optimized conditions, a linear response range from 5 to 476 μmol L−1 was obtained with a limit of detection and sensitivity of 0.56 μmol L−1 and 0.023 μA L μmol−1, respectively. The relative standard deviation for 10 determinations of 100 μmol L−1 isoniazid was 2.5%. The sensor was successfully applied for isoniazid selective determination in simulated body fluids.

We report on the synthesis and electrochemical properties of diamond grown onto vertically aligned carbon nanotubes with high surface areas as a template, resulting in a composite material exhibiting high double-layer capacitance as well as low electrochemical impedance electrodes suitable for applications as supercapacitor devices. We contrast results from devices fabricated with samples which differ in both their initial substrates (Si and Ti) and their final diamond coatings, such as boron-doped diamond and diamond-like carbon (DLC). We present for first time a conducting model for non-doped DLC thin-films. All samples were characterized by scanning and transmission electron microscopy and Fourier transform infrared and Raman spectroscopy. Our results show specific capacitance as high as 8.25 F g−1 (∼1 F cm−2) and gravimetric specific energy and power as high as 0.7 W h kg−1 and 176.4 W kg−1, respectively, which suggest that these diamond/carbon nanotube composite electrodes are excellent candidates for supercapacitor fabrication.

A novel thin solid film of interconnected carbon nanospheres (ICNS) has been developed and characterized as electrode. The thin film is composed of interconnected carbon nanospheres with average crystallite size of ~ 5 nm and laminar graphene layers separated by an interplanar spacing of ~ 0.32 nm. An electrode was prepared in a one-step process by depositing ICNS onto a niobium substrate by hot filament chemical vapour deposition. To prepare an electrode, solvent-refined oil without additives was annealed up to 530 °C under ~ 2700 Pa of a gas mixture containing ethanol, methanol, water, and boron trioxide. The resulting ICNS film was characterized by scanning and transmission electron microscopy, plus Raman, Fourier transform infrared and energy dispersive spectroscopies. The contact angle between deionized water and the ICNS surface was zero - the water droplet instantaneously spread over the sample surface indicating a hydrophilic surface. The film behaviour as an electrochemical electrode was studied by cyclic voltammetry and electrochemical impedance spectroscopy. ICNS layers exhibited a large potential window, low uncompensated resistance, as well as low charge-transfer impedance in the presence of ferrocene-methanol or ferrocyanide as redox probes. These useful properties make ICNS electrodes very promising for future applications in electrocatalysis and (bio)sensors.

We report on the synthesis and electrochemical properties of multi-walled carbon nanotubes (MWCNTs) for supercapacitor devices. Freestanding vertically-aligned MWCNTs and MWCNT powder were grown concomitantly in a one-step chemical vapour deposition process. Samples were characterized by scanning and transmission electron microscopies and Fourier transform infrared and Raman spectroscopies. At similar film thicknesses and surface areas, the freestanding MWCNT electrodes showed higher electrochemical capacitance and gravimetric specific energy and power than the randomly-packed nanoparticle-based electrodes. This suggests that more ordered electrode film architectures facilitate faster electron and ion transport during the charge–discharge processes. Energy storage and supply or supercapacitor devices made from these materials could bridge the gap between rechargeable batteries and conventional high-power electrostatic capacitors.

We have prepared a novel 3D porous biomaterial combining poly ( dl -lactic acid) (PDLLA) and graphene and multi-walled carbon nanotubes oxides (MWCNTO-GO) composite. PDLLA as control and a high loading of PDLLA/MWCNTO-GO (50/50 w/w) bioscaffolds were prepared and functionalized. MWCNTs were exfoliated to form MWCNTO-GO by oxygen plasma etching. The later was also applied to enhance the scaffolds wettability, attaching oxygen-containing groups on their surfaces. This approach produced a porous architecture observed by scanning electron microscopy and semi-quantified by electrochemical analysis. The later also indicated a notable increase on the conductivity of PDLLA/MWCNTO-GO scaffold compared to MWCNTO-GO free PDLLA (about 5 orders of magnitudes at low frequencies). Thermogravimetric analysis showed that the MWCNTO-GO acted protecting the PDLLA matrix, enhancing its thermal stability. The PDLLA/MWCNTO-GO scaffolds had significant cellular adhesion, did not present cytotoxicity effect, besides reduced bactericidal proliferation and produced mineralized tissues in SBF media. The metallic MWCNTO-GO powder held together by PDLLA polymer opens a whole new branch of applications, including bioelectroanalyses, drug delivery systems and tissue engineering.

Nano-calcium-phosphate (n-CaP) is an attractive, biocompatible material for increasing osteointegration. Among nanomaterials, functionalized carbon-based materials are emerging materials, which have excellent mechanical properties, biocompatibility and chemical stability. These properties may further enhance the n-CaP performance. It has been shown that stoichiometric n-CaP can be electrodeposited on graphene and carbon nanotubes (CNTs) by employing fast and low-cost electrodeposition techniques. Here, we present, for the first time, a crystalline, needle-like nano-β-tricalcium phosphate (n-β-TCP) electrodeposited on reduced graphene oxide (rGO) nanosheets. The rGO was grown on CNT, as a composite biomaterial, in a one-step process, followed by electrodeposition of n-CaP. The results show that, in acidic pH, needle-like crystals appear on the surface. It is speculated that the carboxyl (carboxylic acid)/carboxylate functional groups attached directly to the rGO are essential in accelerating OH – formation and deposition of needle-like n-CaP crystals. High-resolution scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction elucidated homogeneous, highly crystalline, n-CaP (β-tricalcium phosphate) crystals. This composite presented an excellent in vitro biomineralization after soaking in simulated body fluid.

Porous boron-doped diamond (p-BDD) electrodes of high-surface-area have been prepared on vertically aligned carbon nanotube substrates, and their electrochemical performance has demonstrated promising results for application in electroanalysis. The electrochemical features of the p-BDD electrodes were investigated and compared with those of a conventional flat BDD electrode (f-BDD). From cyclic voltammetry studies performed for the electrochemical probes [Fe(CN)6]3− and N,N,N′,N′-tetramethyl-para-phenylenediamine (TMPD), a fast charge transfer was observed at the p-BDD/electrolyte interface. For the [Fe(CN)6]3− redox probe, the heterogeneous electron-transfer rate constant (k 0) value obtained for p-BDD was 10.9 times higher than that obtained using a f-BDD electrode. Moreover, the p-BDD electrodes also gave a smaller peak potential separation, ΔE p, and larger analytical signal magnitude for different biomolecules, such as dopamine (DA), acetaminophen (AC), and epinephrine (EP). These set of results demonstrated that the p-BDD electrode is a suitable candidate for applications in electroanalytical chemistry.

We report on novel multi-walled carbon nanotubes (MWCNTs) and activated carbon (AC) composite material as electrode for electrochemical capacitors (ECs). Here MWCNTs work simultaneously as binder and additive for AC electrodes. MWCNTs were synthesised directly onto AC placed on nickel coated aluminium foils binding all of them. During MWCNT synthesis, nickel coated aluminium foils were converted on nickel aluminide alloy, which is extremely stable in neutral aqueous media and also permit welding in the case of large devices manufacturing or association. This novel material brings two significant features to ECs devices: (i) very low equivalent series resistance, and (ii) operational stability in aqueous based electrolytes. That is an excellent opportunity to explore because nonaqueous electrolytes itself and its handling to keep them humidity-free are ones of the most expensive part of ECs manufacturing. Replacing them using a better cost-effective and environmentally friendly electrolyte is desirable. Our approach is simple, fast, very reproducible, and low cost and in the end of the day devices showed large cell voltage of 1.5 V in aqueous electrolyte with specific capacitance of electrode material up to 105 F g−1 (e.g. very similar to several reports on literature using standard binders). Our cyclability test suggested a long service life with no significative lost on capacitance retention after 70 thousand cycles using a voltage range of 1.5 V at 25 A g-1. A detailed electrochemical analysis of device is also presented. On the Ragone plot, our devices fit between Li-ion capacitor and electrochemical capacitors.

In this work, an electrochemical sensor based on vertically oriented carbon nanotubes (voMWCNT), electrically wired via connection upon a copper plate, for the detection of tadalafil (TD) is reported. The voMWCNT is easily prepared via microwave plasma reactor with no additional post-treatment. The voMWCNT was characterized by scanning and transmission electron microscopy in addition to electrochemical characterization with cyclic voltammetry. Once TD is of easy access and used in the treatment of erectile dysfunction and related diseases, the quality control of this drug is of high importance. Using linear sweep voltammetry, the detection of TD was found to be possible from 0.85 to 8.9 μmol L−1, with an R2 of 0.992 with a limit of detection found to correspond to 78 nmol L−1. The quantification of TD in different pharmaceutical drugs, as well as the device stability, indicates that the voMWCNT has potential for the routine sensing of TD.

We report on the synthesis, characterization of nickel hydroxide and manganese oxide nanoparticles decorating multiwalled carbon nanotubes composite material, and electrochemical performance for energy storage processes in symmetric electrochemical capacitors. A large pseudocapacitive voltage range of 1.7 V is presented using a coin cell containing a 1.0 M Li2SO4 aqueous solution, resulting in a maximum specific capacitance of ~ 420 F g−1 verified at 1.67 A g−1 during the discharge process. The symmetric coin cell was highly stable with a very high coulombic efficiency of ~ 99% even after 70,000 cycles of charge-discharge. The high electrochemical stability of coin cell was attributed to a synergism between the nanostructured carbon support and metal (hydr)oxides nanoparticles, i.e., the transport of electrons and ions across the porous electrode structure enables with a high degree of reversibility for the solid-state redox transitions reactions, which is the main contribution to the whole electrode specific capacitance. Near-surface structural changes of the electrodes were monitored during dynamic polarization by Raman and XRD synchrotron measurements. The presence of the active Ni–O stretching mode was verified during the charge-discharge processes according to the reversible solid-state redox process. The Raman shifts were also correlated with the reversible intercalation-deintercalation processes of Li+-ions into the MnOx host material, as well as reversible adsorption of solvated ions on the surface defects of carbon nanostructures.

We report in this work the surface chemistry and the electrochemical studies on electrodes composed of randomly oriented multi-walled carbon nanotubes supported on stainless-steel (AISI:ROMWCNTs) confined in symmetric coin cells, before and after the electrode aging process accomplished in aqueous and organic electrolytes. We contrasted features from the as-grown and aged electrodes obtained during the different electrochemical experiments using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy techniques. Also, several studies involving the Raman, Fourier transform infrared, and X-ray photoelectron spectroscopy, and the scanning electron microscopy techniques were carried out. Our experimental findings indicated that the electrode material shows fair good stability during the charge-discharge processes carried out using the different electrolytes. The aging process observed for each electrolyte revealed the formation of reaction by-products during the long-term charge-storage endurance tests. We additionally performed the in situ (operando) Raman characterization study of the electrodes under dynamic polarization conditions. In this sense, we verified the reversible Raman shifts (e.g., G & D bands) accounting for the dynamic nature of the charge accumulation-depletion processes occurring inside the electrical double-layer structure.

This report describes a method to fabricate high-surface-area boron-doped diamond (BDD) electrodes using so-called 'black silicon' (bSi) as a substrate. This is a synthetic nanostructured material that contains high-aspect-ratio nano-protrusions, such as spikes or needles, on the Si surface produced via plasma etching. We now show that coating a bSi surface composed of 15 μm-high needles conformably with BDD produces a robust electrochemical electrode with high sensitivity and high electroactive area. A clinically relevant demonstration of the efficacy of these electrodes is shown by measuring their sensitivity for detection of dopamine (DA) in the presence of an excess of uric acid (UA). Finally, the nanostructured surface of bSi has recently been found to generate a mechanical bactericidal effect, killing both Gram-negative and Gram-positive bacteria at high rates. We will show that BDD-coated bSi also acts as an effective antibacterial surface, with the added advantage that being diamond-coated it is far more robust and less likely to become damaged than Si.

Developing more sustainable, low cost and feasible energy storage devices is a keystone of aerospace, automobile, and electronics industries. In research new materials and techniques that allow their production in large scale are studied by researchers around the world. Regarding materials, supercapacitors, for instance, may have carbon based materials on electrodes, owing to their chemical stability, low cost, and safety; however, their specific capacitance is lower when compared to other materials. Additionally, materials that may provide higher capacitance–due to faradaic or redox reactions – are also studied. Within this group, transition metal oxides are potential candidates for that, once faradaic behavior may provide higher capacitance values; however, not cyclability in most cases. Thus, this work presents a composite material with tungsten carbide (W2C) and tungsten oxide species (WxOy), which showed both faradaic behavior and cyclability. This composite material was synthesized by deposition of tungsten using a technique known as hot filament chemical vapor deposition (HFCVD). In this process, sublimation of tungsten occurred under H2 constant flow; thus, reducing the metallic tungsten; while oxide species were formed by spontaneous passivation. Experimental results indicate that the efficiency improved from 59% to 85% for first and 10, 000th cycles, respectively, with boost of specific capacitance of 160%. In sum, the material reported herein presents the unique aspect of improving its properties during cyclability. Therefore, such feature and synthesis process may enable its use as renewable energy storage devices.

Carbon nanomaterials thin films have been attracted considerable attention in the last years due to relative low cost and excellent electrical conductivity features. We report here on novel sensor architecture consisted of a glassy carbon surface modified with manioc starch and nanodiamonds nanoparticles. Structural and morphological properties of this thin film were investigated by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopies. By using square-wave voltammetry as electroanalytical tool, the widely used herbicide diquat (DQ) was determined in environmental samples. The modified electrode presented a linear response to DQ in the concentration range of 5.0 × 10−7 to 4.6 × 10−5 mol L−1 with a limit of detection of 1.1 × 10−7 mol L−1. This novel sensor proved to be efficient to determine if DQ is present in rivers and drinking water samples.

We report here a method to produce nanostructured and porous electrodes by electrospraying niobium pentoxide nanoparticles onto entangled spaghetti-like multiwalled carbon nanotubes. The novel niobium pentoxide and carbon nanotubes composite material exhibits promising electrode properties for the aqueous-based electrochemical capacitors. Monoclinic and orthorhombic niobium pentoxide nanoparticles are partially covered with a thin carbon layer and anchored onto carbon nanotubes. Not only does this electrode material possess the excellent, well-known characteristics associated with carbon nanotubes (large voltage window and chemical stability), but it also has pseudocapacitive properties due to niobium pentoxide nanoparticles. This approach improves the electrical conductivity and chemical stability and also avoids reaggregation and deactivation of niobium pentoxide nanoparticles. These nanostructured carbon nanotubes and niobium pentoxide composite electrodes are characterized by ex-situ techniques, such as scanning and transmission electron microscopy, Raman, X-ray photoelectron spectroscopy, and X-ray diffraction. In-situ studies are performed on cyclic voltammetry, galvanostatic (re)charge/discharge curves, and electrochemical impedance spectroscopy techniques. Our results show that carbon nanotubes and niobium pentoxide composite has outstanding electrochemical properties, including high specific capacitance (~320 F g−1), long lifespan (more than 100,000 charge and discharge cycles), and high energy and power densities.