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To boost the energy storage of microsupercapacitors (MSCs), a nanocomposite electrode combining carbonaceous materials with metal oxides was developed, i.e. combining capacitive and faradaic currents. Our method involves a one-step hydrothermal process, the initial components being graphene oxide, dopamine and Co2+ ions, resulting in a reduced graphene oxide–polydopamine–Co3O4 composite. Dopamine acts as a reducing agent and prevents graphene oxide agglomeration. Co2+ ions are expected to be chelated by polydopamine, likely leading to uniform dispersion of Co3O4 particles on the graphene surface. Using this composite as an active material, thin film electrodes were prepared, thoroughly characterized via various chemical techniques, and their electrochemical properties were tested in KOH. In situ electrochemical quartz crystal microbalance was used to elucidate the charge storage process, which showed the presence of a "point of maximum mass" separating a dominant anionic contribution due to the pseudocapacitive response of Co3O4 and a cationic contribution reflecting the electroadsorption/desorption of cations on the rGO surface. Lastly, we extended our study to the fabrication of a current collector-free microsupercapacitor device, composed of interdigitated rGO–PDA–Co3O4 electrodes, which demonstrates excellent cycling stability over 3000 cycles at a scan rate of 50 mV s−1 and remarkable energy density of 12.25 mW h cm−3 at a power density of 0.26 W cm−3. [ABSTRACT FROM AUTHOR]

Herein, the development and the characterization of an all‐solid‐state symmetrical and current collector‐free microsupercapacitor based on a new reduced graphene oxide‐polydopamine (rGO‐PDA) composite are reported. The rGO‐PDA composite is synthesized by a facile, eco‐friendly and scalable hydrothermal approach in the presence of dopamine which can not only contribute to the oxygen functional groups removal from graphene oxide but also polymerize onto the rGO sheets reducing their restacking and improving the wettability of the electrode. The optimized rGO‐PDA composite material exhibits excellent capacitance and cycling stability as well as an improved rate capability compared to the pristine rGO in Na2SO4 solution. This performance enhancement can be linked to the higher transfer kinetic and lower transfer resistance values of the ions involved in the charge storage process of rGO‐PDA, as determined by ac‐electrogravimetry. Furthermore, an all‐solid‐state microsupercapacitor was prepared employing the optimized rGO‐PDA composite as electrode material. Interdigitated electrodes were obtained thanks to a CO2 laser and a Na2SO4/PVA hydrogel was employed, no current collector was used. This device achieves a noteworthy energy density of 6.2 mWh ⋅ cm−3 at a power density of 0.22 W ⋅ cm−3. Moreover, it exhibits exceptional cycling stability, retaining 104 % of its initial capacity even after undergoing 10,000 cycles at 2 V ⋅ s−1. [ABSTRACT FROM AUTHOR]

To reach a deeper understanding of the charge storage mechanisms of electrode materials is one of the challenges toward improving their energy storage performance. Herein, we investigate the interfacial ion exchange of a composite electrode made of carbon nanotube/poly(ortho-phenylenediamine) (CNT/PoPD) in a 1M NaCl aqueous electrolyte via advanced electrogravimetric analyses based on electrochemical quartz crystal microbalance (EQCM). Classical EQCM at different scan rates of the potential revealed the complex electrogravimetric behavior likely due to multi-species participation at different temporal scales. Thereafter, in order to better understand the behavior of each species (ions, counter ions, and co-ions) in the charge compensation mechanism, the electrogravimetric impedance spectroscopy analysis (also called ac-electrogravimetry) was pursued. Ac-electrogravimetry revealed the role of each species where Na+ cations and Cl− anions as well as protons participate in the charge compensation mechanism of the CNT/PoPD composite with different kinetics and proportions. The water molecules with opposite flux direction with the cations are also detected, suggesting their exclusion during cationic species transfer. Having analyzed ac-electrogravimetry responses in depth, the synergistic interaction between the CNT and PoPD is highlighted, revealing the improved accessibility of species to new sites in the composite. [ABSTRACT FROM AUTHOR]

In this study, fast controlled precipitation (FCP) and chronoamperometry (CA) methods were performed to evaluate the influence of the magnetic treatment at 0.70 T, upon the scale formation in synthetic solutions (hardness 25 °F), exposed to a static magnetic field for different exposure times. According to FCP results, homogeneous CaCO3 precipitation rates in treated solution were lower than those in the absence of the magnetic field. It has been found that the memory effect can last up to 24 h after the magnetic treatment even if it decreases over time. As purpose of comparison, CA method was applied to investigate the influence of the magnetic treatment on heterogeneous CaCO3 precipitation. The magnetic field effect increased with the increasing exposure time. The obtained scale, characterized by scanning electronic microscopy and X‐ray diffraction, was formed by a mixture of calcite and aragonite in the presence of magnetic field. [ABSTRACT FROM AUTHOR]

An ultrahigh performance impedimetric DNA sensor is presented showing detection limits in the femtomolar range. This electrochemical setup was constructed initially by electrogeneration of poly(ll-pyrrol-l-yl-undecanoic acid [N.sub.[alpha]'], [N.sub.[alpha]]-bis(carboxymethyl)-L-lysine amide) (poly(pyrrole-NTA)) film. The latter was then modified by the coordination of [Cu.sup.2+] ions onto the chelating NTA centers followed by the immobilization of the ssHIVDNA previously modified by a polyhistidine tag by affinity binding. The immobilization of the DNA probe and hybridization with the complementary target ssHIV-DNA were investigated using fluorescence microscopy and quantified with quartz crystal microbalance experiments leading to DNA probe and duplex coverage of 1.7 x [10.sup.-11] and 7.7 x [10.sup.-12] mol [cm.sup.-2], respectively. The duplex formation was corroborated by amperometric measurements through the duplex labeling by a glucose oxidase. In the presence of hydroquinone as redox indicator, the DNA sensor was applied to the impedimetric detection of target DNA without a labeling step. A linear quantification of the HIV DNA target was carried out in the range [10.sup.-15] to [10.sup.-8] mol [L.sup.-1]. 10.1021/ac9024329

In this study, microbalance measurements with a GaP[O.sub.4] crystal were performed to determine the dissolution rate of cerium oxide thin films at room temperature after a high temperature treatment of the hydroxide precursor Ce[(OH).sub.4] at 700[degrees]C. The properties of the GaP[O.sub.4] crystal enables gravimetric measurements to be performed after being heated at high temperatures where the classical quartz crystal microbalance irreversibly loses all its piezoelectric properties. The GAP[O.sub.4] resonators were calibrated at room temperature by galvanostatic copper deposition before and after a high-temperature treatment, and the sensitivity coefficients Ks were found to be identical, which proved the high potential of GaP[O.sub.4] at high temperatures. However the accuracy of the gravimetric measurements is lower after a high temperature treatment. The rate determining step of the cerium oxide dissolution seems to be the reduction reaction of Ce(IV) to Ce(III), which is carried out by the hydrogen peroxide present in the dissolution medium.

Laser photoablation of poly(ethylene terephthalate) (PET), a flexible dielectric organic polymer, was used to design an acoustic miniaturized DNA biosensor. The microchip device includes a 100-[micro]m-thick PET layer, with two microband electrodes patterned in photoablated microchannels on one side and a depressed photoablated disk decorated by gold sputtered layer on the other side. Upon application of an electric signal between the two electrodes, an electroacoustic resonance phenomenon at ~30 MHz was established through the microelectrodes/PET/ gold layer interface. The electroacoustic resonance response was fitted with a series RLC motional arm in parallel with a static Co arm of a Buttlerworth-Van Dyke equivalent circuit: admittance spectra recorded after successive cycles of DNA hybridization on the gold surface showed reproducible changes on R, L, and C parameters. The same hybridizations runs were performed concomitantly on a 27-MHz (9 MHz, third overtone) quartz crystal microbalance in order to validate the PET device developed for bioanalysis applications. The electroacoustic PET device, ~100 times smaller than a microbalance quartz crystal, is interesting for the large-scale integration of acoustic sensors in biochips.

A design method that uses a Miller oscillator as a quartz crystal microbalance (QCM) sensor in liquid media is investigated. Miller oscillator topology shows a good capacity to work under sensor damping.

Various electrogravimetric techniques in ac and dc modes are used to observe and study the changes in the electrical and optical properties of hexacyanoferrate (Prussian Blue) materials during an in situ compositional modulation and the transition region. The analysis and the results obtained have proved to be very useful for the study of molecular cyanide materials and also for a better understanding of the mechanisms involved in the electrochemical reversible switch between para- and ferrimagnetism.