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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]

Aqueous zinc ion batteries (ZIBs) are currently gaining a significant amount of attention as a low‐cost and high safety energy storage option. While mostly inorganic structures are used as cathode materials in aqueous zinc batteries, these materials undergo structural degradation, therefore, alternative organic cathodes are expected to be developed to replace inorganic materials in aqueous zinc ion batteries (AZIBs). In this work, pillar[5]quinone (P5Q) is used as a cathode in AZIBs for the first time. Besides investigating the charge storage mechanism and interfacial property evolution of P5Q by various ex situ analyses, electrochemical quartz crystal microbalance (EQCM) and density functional theory (DFT) demonstrates both Zn2+ and H+ incorporation. The P5Q exhibits >99 % Coulombic efficiency through 10000 cycles at ultra‐fast (500 °C) current density, yielding a capacity value of approximately 120 mAh g−1 at the end of the cycle. When the current density is changed from 500 °C to 120 °C, an initial discharge capacity of approximately 182 mAh g−1 is achieved, demonstrating outstanding performance with over 80 % capacity retention for the subsequent 7000 cycles. [ABSTRACT FROM AUTHOR]

The effects of current collectors on the battery performance have significant role, especially in aqueous electrolyte Al-ion batteries, as corrosion effects lead to rapid capacity degradation over cycles. To overcome this problem, we present a study investigating the selection of suitable current collectors and their impact on battery performance. Four different current collectors are selected for this. Stainless steel (SS), nickel foil (Ni), titanium foil (Ti) and graphite plate (GP). It has been proven by corrosion tests, cyclic voltammetry and charge-discharge studies that GP is the best current collector by minimizing the corrosion effect and H2 evolution reaction (HER). The anatase phase TiO2 used with GP current collector provides a 249 mAh g−1 initial discharge capacity at a current density of 3 A g−1, while inferior or no electrochemical activity is observed with Ti, SS, Ni current collectors. The observations here provide insights into the selection of corrosion-resistant current collectors to achieve stable battery performance in the field of aqueous electrolyte Al-ion batteries. [ABSTRACT FROM AUTHOR]

Nafion has been dominating the proton exchange membrane (PEM) market because of its adequacy for the proton exchange operation. However, because of its high cost, low performance at low relative humidity, and finally environmental unfriendliness, researchers have been developing and working on Nafion alternatives. In this review, we assess how biopolymers present an opportunity as an eco‐friendly material able to replace the conventional Nafion membrane in proton exchange membrane fuel cells (PEMFC). Chitosan and cellulose were the most studied in literature owing to their abundance in nature, low cost, and high affinity for water, which are sought‐after properties for PEM. In addition to that, their ease of modification through their hydroxyl or amine groups represents an opportunity to further enhance their characteristics and thus meet the criteria of diverse applications. The use of biopolymers as an adequate PEM is facing many challenges. Having a practical proton conductivity and securing the physicochemical stability of the biopolymers in fuel cell operating conditions are two of the most important challenges to overcome. Promising strategies to simultaneously address these challenges such as crosslinking, making interpenetrated networks, and making blends and composites are reported. [ABSTRACT FROM AUTHOR]

Fe(II)-carbonates, such as siderite, form in environments where O2 is scarce, e.g., during marine sediment diagenesis, corrosion and possibly CO2 sequestration, but little is known about their formation pathways. We show that early precipitates from carbonate solutions containing 0.1M Fe(II) with varying pH produced broad peaks in X-ray diffraction and contained dominantly Fe and CO3 when probed with X-ray photoelectron spectroscopy. Reduced pair distribution function (PDF) analysis shows only peaks corresponding to interatomic distances below 15Å, reflecting a material with no long range structural order. Moreover, PDF peak positions differ from those for known iron carbonates and hydroxides. Mössbauer spectra also deviate from those expected for known iron carbonates and suggest a less crystalline structure. These data show that a previously unidentified iron carbonate precursor phase formed. Its coherent scattering domains determined from PDF analysis are slightly larger than for amorphous calcium carbonate, suggesting that the precursor could be nanocrystalline. Replica exchange molecular dynamics simulations of Fe-carbonate polynuclear complexes yield PDF peak positions that agree well with those from experiments, offering the possibility that the material is a condensate of such complexes, assembled in a relatively unorganised fashion. If this is the case, the material could be nearly amorphous, rather than being composed of well defined nanocrystals. PDF measurements of samples ageing in solution coupled with refinement with the software PDFgui show that the material transforms to siderite or siderite/chukanovite mixtures within hours and that the transformation rate depends on pH. The identified Fe-carbonate precursor may potentially form during anaerobic corrosion or bacterial Fe reduction.

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]

Reliable operation of Na‐ion batteries requires a mastering of the interfacial processes governing intercalation kinetics. Ion desolvation, amongst others, is a crucial phenomenon as far as power applications are envisioned. Studying the intricacies of interfacial processes faces experimental challenges. Here the complementary use of electrochemical quartz crystal microbalance (EQCM) and operando infrared fiber evanescent wave spectroscopy (IR‐FEWS) combined with molecular dynamics (MD) simulations is reported to investigate the electrode/electrolyte interface of polyanionic Na‐insertion compounds Na3V2(PO4)3 (NVP) and Na3V2(PO4)2F3 (NVPF). Through screening of various electrolytes that differ in their solvation energy and viscosity, the existence of an unusual mass uptake/depletion signal is demonstrated at the NVP interfaces only, indicative of a dissimilarity in migration kinetics of solvent molecules between NVP and NVPF interfaces as supported by IR‐FEWS. This finding is rationalized by positing that sodium depletion is caused by the unusually rapid ion diffusion within NVP mediated by an intermediate metastable phase, which leads to opposite Na+ concentration and free solvent molecule gradients at the interface that causes the unusual and anomalous feature observed on EQCM frequency profiles. This feature does not appear with NVPF showing lower ionic diffusion. Altogether, this fundamental study provides valuable fundamental insights into the interface structuring of insertion compounds depending upon their Na+ mobility. [ABSTRACT FROM AUTHOR]