We report for the first time on in situ transduction of electrochemical responses of ion-selective electrodes, operating under non-zero-current conditions, to emission change signals. The proposed novel-type PVC-based membrane comprises a dispersed redox and emission active ion-to-electron transducer. The electrochemical trigger applied induces a redox process of the transducer, inducing ion exchange between the membrane and the solution, resulting also in change of its emission spectrum. It is shown that electrochemical signals recorded for ion-selective electrodes operating under voltammetric/coulometric conditions correlate with emission intensity changes recorded in the same experiments. Moreover, the proposed optical readout offers extended linear response range compared to electrical signals recorded in voltammetric or coulometric mode.

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A new concept of easy to make, potentially disposable potentiometric sensors is presented. A thermoprocessable carbon black-loaded, electronically conducting, polylactide polymer composite was used to prepare substrate electrodes of user’s defined shape/arrangement applying a 3D pen in a hot melt process. Covering of the carbon black-loaded polylactide 3D-drawn substrate electrode with a PVC-based ion-selective membrane cocktail results in spontaneous formation of a zip-lock structure with a large contact area. Thus, obtained ion-selective electrodes offer sensors of excellent performance, including potential stability expressed by SD of the mean value of potential recorded equal to ±1.0 mV (n = 6) within one day and ±1.5 mV (n = 6) between five days. The approach offers also high device-to-device potential reproducibility: SD of mean value of E 0 equal to ±1.5 mV (n = 5).

A novel approach to electrochemical determination of volatile organic compounds (VOCs) suspended in a solution is proposed. This approach benefits from properties of capacitors linked in series, where the total capacitance is affected by analyte induced changes. A tailor designed hydrophobic PVDF membrane modified with polyoctylthiophene used in this arrangement played a role of a bipolar electrode. The presence of water immiscible liquid VOCs results in spontaneous formation of a thin film on the surface of the hydrophobic polymer membrane and dissolution of modifying particulates. This effect leads to change of electrical parameters of the system: capacitance and resistance dependent on amount of VOCs present in the aqueous phase.

The applicability of emission readout of ion‐selective electrodes, containing fluorimetrically active polyoctylthiophene in the membrane, operating under chronopotentiometric mode was studied. The electrochemical and optical signals were collected in the same experiment and compared. In both modes a change in recorded signal: potential or emission in time was observed while a constant current was applied to the sensor. The recorded signals (chronopotentiometric, fluoro‐chronopotentiometric curves and calculated transition times) were dependent on the concentration of potassium ions. The transition times calculated from electrochemical signals were linearly dependent on the concentration of potassium ions in solution within the range: 0.1–0.7 mM. Optically read transition times were also linearly dependent on concentration within the same range, however, they were shorter than those recorded electrochemically. This difference is attributed to various effects represented by the transition time: concentration increase of reduced form of the conducting polymer in the optical mode or depletion of potassium ions close to the membrane surface, in the electrochemical mode.

There has been progress and growing interest in the development of novel and efficient energy storage systems meeting high power and energy demands of modern devices and advanced technologies. Among important requirements for such charge storage devices are high volumetric and gravimetric energy and power, large number of charging/discharging cycles, improved safety and reasonable cost. At the current stage of technology, common charge storage systems, such as batteries and electrochemical capacitors, rarely meet those expectations. Indeed the present systems offer either high energy density (batteries) or high peak power (electrochemical capacitors) but barely both characteristics. Lately, there have been attempts to consider aqueous electrolytes containing dissolved redox species capable of undergoing fast electrode reactions at the interfaces formed with highly porous carbon electrodes. Consequently, the energy density significantly increases while keeping the power performance of a typical double-layer capacitor. Since most of redox-electrolyte-based systems utilize aqueous solutions, such advantages as enhanced safety, environment-friendliness and reasonable cost could be retained. Such redox-active species as iodide, quinone, phenelenediamine, ferrocyanide, methylene blue, thiocyanide and cerium sulphate have been successfully applied as positive or negative electrode-supporting electrolytes. The redox processes (battery-type characteristics) are typically observable in the potential range of a single electrode only and, therefore, the opposite electrode operating according to the electrical double-layer mechanism (capacitive behavior) limits the overall cell performance in terms of capacity and energy. To overcome this drawback, application of dual redox-type electrolytes comprising two independent redox couples separated in the positive and negative electrode compartments has been recently proposed. From the mechanistic point of view, such devices resemble conventional redox-flow batteries but operating in static conditions, i.e. more favourable from the practical and economical point of view. By taking into account the above deliberations, a dual redox-active (proton-conductive) electrolyte composed of the mixture of two different soluble redox species is considered here for application in energy storage devices with an enhanced specific energy [1]. The Keggin-type polyoxometalate (phosphotungstic acid), undergoing fast (electrochemically reversible) one-electron redox processes has been selected to support the negative electrode. In order to develop the potential difference in the cell, the hydroquinone, capable of oxidation/reduction according to the fast two-electron mechanism has been adopted and its electroactivity was predominantly confined to the positive electrode. It enabled us to design a hybrid charge storage cell with the operating voltage of 0.8 V and the specific energy of 20 Wh kg-1 (per total mass of both electrodes). In the constant power discharge mode, 13 Wh kg-1 of the energy has been preserved at the power of 1 kW kg-1 during discharging down to ½ of the maximum voltage which is consistent with the fast charging/discharging dynamics of the proposed hybrid system. A mixed hierarchical micro-porous (predominantly mesoporous) porous carbon of high (>2 cm3g-1) total pore volume and the BET surface area approaching 1000 m2 g-1 has been selected as the electrode material permitting electrical double layer charging and supporting electroactivity of redox species and unimpeded mass transport. Also, the normalization of electrical parameters against the total mass of electrodes and electrolyte resulted in a ca. five-fold increase of discharge capacity and specific energy in comparison to the performance of a simple electrical double-layer capacitor. Acknowledgement Financial support was provided by the National Centre for Research and Development (NCBR, Poland) under Techmatstrateg Grant no. 347431/14/NCBR/2018 as well as by the NCBR in the framework of European Union POWER 3.2 Project no. POWR.03.02.00-00-I007/16-00. 1. M. Skunik-Nuckowska, K. Węgrzyn, S. Dyjak, N. H. Wisińska, P. J. Kulesza, Energy Storage Mater., 21 (2019) 427-438

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