A neutral-pH aqueous redox flow battery based on sustainable organic electrolytes

Aqueous organic redox flow batteries (AORFBs) have gained increasing attention for large-scale storage due to the advantages of decoupled energy and power, safe and sustainable chemistry, and tunability of the redox-active species. Here, we report the development of a neutral-pH AORFB assembled with a highly water-soluble ferrocene 1,1-disulfonic disodium salt (DS−Fc) and two viologen derivatives, 1,1’-bis(3-sulfonatopropyl)-viologen (BSP−Vi) and Bis(3-trimethylammonium)propyl viologen tetrachloride (BTMAP−Vi). Synthesized electrolytes showed excellent redox potential, good diffusion coefficient, and a good transfer rate constant. In particular, BSP−Vi has a more negative redox potential (-0.4 V) than BTMAP−Vi (−0.3 V) and faster kinetics; therefore, it was selected to be assembled in an AORFB as anolyte, coupled with DS−Fc as catholyte.The resulting AORFB based on BTMAP−Vi/DS−Fc and BSP−Vi/DS−Fc redox couple had a high cell voltage (1.2 V and 1.3 V, respectively) and theoretical energy density (13 WhL−1 and 14 WhL−1 respectively) and was able to sustain 70 charge-discharge cycles with energy efficiency as high as 97 %

Artificial photosynthesis: photoanodes based on polyquinoid dyes onto mesoporous tin oxide surface

Dye-sensitized photoelectrochemical cells represent an appealing solution for artificial photosynthesis, aimed at the conversion of solar light into fuels or commodity chemicals. Extensive efforts have been directed towards the development of photoelectrodes combining semiconductor materials and organic dyes; the use of molecular components allows to tune the absorption and redox properties of the material. Recently, we have reported the use of a class of pentacyclic quinoid organic dyes (KuQuinone) chemisorbed onto semiconducting tin oxide as photoanodes for water oxidation. In this work, we investigate the effect of the SnO2 semiconductor thickness and morphology and of the dye-anchoring group on the photoelectrochemical performance of the electrodes. The optimized materials are mesoporous SnO2 layers with 2.5 mu m film thickness combined with a KuQuinone dye with a 3-carboxylpropyl-anchoring chain: these electrodes achieve light-harvesting efficiency of 93% at the maximum absorption wavelength of 533 nm, and photocurrent density J up to 350 mu A/cm(2) in the photoelectrochemical oxidation of ascorbate, although with a limited incident photon-to-current efficiency of 0.075%. Calculations based on the density functional theory (DFT) support the role of the reduced species of the KuQuinone dye via a proton-coupled electron transfer as the competent species involved in the electron transfer to the tin oxide semiconductor. Finally, a preliminary investigation of the photoelectrodes towards benzyl alcohol oxidation is presented, achieving photocurrent density up to 90 mu A/cm(2) in acetonitrile in the presence of N-hydroxysuccinimide and pyridine as redox mediator and base, respectively. These results support the possibility of using molecular-based materials in synthetic photoelectrochemistry.[GRAPHICS]

KuQuinones: a ten years tale of the new pentacyclic quinoid compound

Quinones are widespread in nature, as they participate, mainly as redox mediators, in several biochemical processes. Up to now, various synthetic quinones have been recommended in the literature as leading molecules in energy, biomedical and catalytic fields. In this brief review, we retraced our research activity in the last ten years, mainly dedicated to the study of a new class of peculiar pentacyclic conjugated quinoid compounds, synthesized in our group. In particular, their application as sensitive materials in photoelectrochemical devices and in biosensors, as photocatalysts in selective oxidation reactions, and their anticancer activity is here reviewed

KuQuinone as a highly stable and reusable organic photocatalyst in selective oxidation of thioethers to sulfoxides

A chemoselective photocatalytic system to perform thioether oxidation to sulfoxide is presented. The light-induced oxidation process is here promoted by a metal-free quinoid catalyst, namely 1-hexylKuQuinone (KuQ). Reactions performed in a fluorinated solvent (i.e., HFIP), using O2 as the oxidant, at room temperature, lead to complete thioanisole conversion to methyl phenyl sulfoxide in 60 min. Remarkably, the system can be recharged and recycled without a loss of activity and selectivity, reaching turnover numbers (TONs) higher than 4000. Excellent catalytic performances and full selectivity have also been obtained for the photocatalytic oxidation of substituted thioanisole derivatives, aliphatic, cyclic, and diaryl thioethers. Likewise, the oxidation of heteroaromatic organosulfur compounds can be accomplished, with longer reaction times

Carbon-black combined with TiO2 and KuQ as sustainable photosystem for a reliable self-powered photoelectrochemical biosensor

Since our first work published in Electrochemistry Communication in 2010 (12, 346–350), many carbon black-(CB) based electrochemical printed (bio)sensors have been reported in the literature, addressing voltammetric and potentiometric measurements. Herein, we report the first photoelectrochemical biosensor based on a printed electrode modified with CB. In detail, the photoelectrochemical sensor has been designed by using, in addition to CB, and TiO2, KuQ dye because the use of only TiO2 and CB still requires UV irradiation, while KuQ is characterized by a broad and intense absorption spectrum in the visible region allowing for an easy set-up with a costeffective portable laser. Once optimized the fabrication and working conditions, namely the solvent for the TiO2 dispersion (i.e. water/dimethylformamide (1:1 v/v)), the amount of TiO2/KuQ to cast onto the working electrode surface (i.e. 4 μg), the applied potential (i.e. +0.4 V), and the working solution (i.e. Tris buffer at pH 8.8), the sensor was challenged for NADH measurement obtaining a linear range up to 8 mM and a detection limit, calculated as 3 σb/slope, equal to 20 μM. The subsequent immobilization of Alcohol Dehydrogenase demonstrated the capability of this biosensor to detect ethanol up to 1 M, with the detection limit equal to 0.062 mM, indicating that the CB-TiO2/KuQ modification can regenerate the coenzyme even in the immobilized form, with improved analytical performances in terms of enhancement of the linearity. Finally, ethanol was detected in a real sample, i.e. white wine, with a good recovery value of 91.60 ± 0.01%, demonstrating the applicability of the developed miniaturized biosensor in white wine samples