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Solar redox flow batteries are a relatively new type of redox flow battery technology that uses solar energy to directly store chemical energy. Here we present a solar redox flow battery that uses a MoS 2 @TiO 2 thin film with a Nafion protection layer supported on FTO glass substrate as photoanode, employing VO2+/VO 2 + and AQDS/AQDS2− as redox active species. When the solar radiation strikes the photoelectrode, the photogenerated holes oxidize VO2+ to VO 2 +, while the photogenerated electrons reduce AQDS to AQDS2− at the counter electrode. The oxidized form of V5+ and reduced form of AQDS2− thus retain the chemical energy and can release the stored charged via the reverse electrochemical reaction. The addition of NH 4 Cl to the electrolyte was found to have a positive impact on the electrochemical performance of the redox flow cell. This effect was more evident for the VOSO 4 electrolyte, leading to an enhancement of the voltaic and energy efficiencies of more than 17.5%. The results suggest that NH 4 Cl promotes both mass transport of the vanadium redox species and charge transfer of the AQDS in the electrolyte. The solar-to-output energy conversion efficiency (SOEE) of the solar redox flow battery using 1.6 g L−1 NH 4 Cl in both anolyte and catholyte reached 9.73%, and an energy density of 87.45% after 10 consecutive one-hour photocharging cycles. Additionally, the use of Nafion to protect the MoS 2 @TiO 2 photoanode from photocorrosion was explored. The Nafion layer ensured an increased stability of MoS 2 @TiO 2 against the strong acidic environment while maintaining effective light response, which translated into enhanced photon and mass transport. An energy storage capacity of ∼60 mAh L−1 after 1-hour photocharging was observed. [ABSTRACT FROM AUTHOR]

Electrospinning is fast finding its way as one of the preferred manufacturing techniques to process advanced materials for energy-storage applications. This is due to its remarkable advantages in terms of high versatility to produce free-standing nanofibre materials with controlled composition, porous microstructure and thickness. Among the different devices that can benefit from this technique, redox flow batteries are an emerging grid-scale energy- storage technology that uses electrodes consisting of commercially available carbon felts, cloths or papers. These materials exhibit relatively good stability and low cost. However, their activity towards relevant redox reactions is often poor, which leads to low-power densities and voltage efficiencies. Attempts to improve the electrochemical activity via thermal treatment or deposition of electrocatalytic species have produced mixed results. In addition, the microstructure and void volume are key properties that need optimisation to achieve effective mass transport. The electrodes act as porous media, providing heterogeneous interaction between the electrolyte and exposed catalytic sites. Therefore, the ability to control properties such as porous volume, specific surface area and tortuosity is highly desirable to minimise transport-limited inefficiencies and parasitic pumping losses. This opinion paper explores the potential of electrospun carbon materials to replace commercial carbons as electrodes for redox flow batteries, examining advantages, disadvantages and challenges. [ABSTRACT FROM AUTHOR]

Operando and in situ characterisation studies with the assistance of high energy light produced by synchrotrons are becoming increasingly attractive in the energy storage area, allowing for nondestructive investigations of material properties and device behaviour in realistic working environments, and with high temporal resolution afforded by the latest generation of high-flux beamlines. Many operando synchrotron techniques are well suited to redox flow batteries, which undergo redox changes of the active species in their electrolytes when flowed through porous electrodes. There is a large variety of redox flow battery designs and chemistries, spanning transition metal solutions, hybrid gas-liquid devices, plating and stripping mechanisms and organic redox species. This review presents an overview of recent progress and preponderance of synchrotron techniques in investigating the current issues of redox flow batteries. For each synchrotron X-ray analytical approach, practical examples and breakthrough findings are outlined and the potential applications on the newly developed redox flow batteries are discussed. [ABSTRACT FROM AUTHOR]