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Phenazines are an emerging class of organic compounds that have been recently utilized in aqueous redox flow batteries, a promising technology for large-scale energy storage. A virtual screening based on density functional theory calculations is used to investigate the redox potentials of around 100 phenazine derivatives in aqueous media containing various electron-donating or electron-withdrawing groups at different positions. The calculations identify the crucial positions that should be functionalized with multiple hydroxy groups to design new anolytes. The combined experimental–computational methodology reported herein guides the development of a new molecule with a record low reversible redox potential as a potential anolyte for aqueous redox flow batteries., The authors thank the TALENTO grant (2017-T1/AMB-5264 & 2021-5A/AMB-20946) from Comunidad de Madrid for financial support. The authors also thank the Spanish Ministry of Science and Innovation (MCIN/AEI/FEDER) for financial support through the OMBAT project (Ref.PID2021-124974OB-C21, PID2021-124974OB-C22).

Aqueous hybrid Zn2+/Na+ion batteries (AHZSIBs) have gained considerable attention for stationary energy storage applications because of their outstanding safety, sustainability, abundance, and low raw material costs. However, the low capacity values (+ion deinsertion/insertion cathodes limit the overall capacity storage of AHZSIBs. Herein, we propose a novel concept to extend the charge storage performance of AHZSIBs using electrolyte with redox characteristics. The benefits of using redox aqueous electrolytes such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) and sodium ferrocyanide (Na4[Fe(CN)6]) were investigated in an AHZSB, which consists of Zn metal as an anode and sodium nickel hexacyanoferrate (Na-NiHCF) as the Na+deinsertion/insertion cathode. The proposed AHZSB using Na4[Fe(CN)6] redox electrolyte provided a capacity (144mAh/g) that was ~2.94 times higher than AHZSIB using a conventional Na2SO4electrolyte (49mAh/g). This capacity enhancement emanated from the faradaic contribution of the Fe2+(CN)64−/Fe3+(CN)63−redox pair present in the electrolyte and Fe2+/Fe3+redox pair in the lattice of Na-NiHCF. In addition, the TEMPOL-based redox electrolyte also improved the capacity (from 49 to 120mAh/g) through the combined faradaic contribution of the TEMPOL/TEMPOL+redox pair dissolved in the electrolyte and the Fe2+/Fe3+redox pair in the Na-NiHCF lattice. These results confirm the competence of the redox electrolyte in AHZSIB in enhancing the charge storage capacity. We anticipate that this proof-of-concept study will provide a new direction for developing high-capacity storage AHZSIBs. More importantly, this approach can be used in any aqueous/non-aqueous batteries.

Flexible and scalable energy storage solutions are necessary for mitigating fluctuations of renewable energy sources. The main advantage of redox flow batteries is their ability to decouple power and energy. However, they present some limitations including poor performance, short-lifetimes, and expensive ion-selective membranes as well as high price, toxicity, and scarcity of vanadium compounds. We report a membrane-free battery that relies on the immiscibility of redox electrolytes and where vanadium is replaced by organic molecules. We show that the biphasic system formed by one acidic solution and one ionic liquid, both containing quinoyl species, behaves as a reversible battery without any membrane. This proof-of-concept of a membrane-free battery has an open circuit voltage of 1.4 V with a high theoretical energy density of 22.5 WhL-1, and is able to deliver 90% of its theoretical capacity while showing excellent long-term performance (coulombic efficiency of 100% and energy efficiency of 70%).

Flexible and scalable energy storage solutions are necessary for mitigating fluctuations of renewable energy sources. The main advantage of redox flow batteries is their ability to decouple power and energy. However, they present some limitations including poor performance, short-lifetimes, and expensive ion-selective membranes as well as high price, toxicity, and scarcity of vanadium compounds. We report a membrane-free battery that relies on the immiscibility of redox electrolytes and where vanadium is replaced by organic molecules. We show that the biphasic system formed by one acidic solution and one ionic liquid, both containing quinoyl species, behaves as a reversible battery without any membrane. This proof-of-concept of a membrane-free battery has an open circuit voltage of 1.4 V with a high theoretical energy density of 22.5 Wh L-1 , and is able to deliver 90 % of its theoretical capacity while showing excellent long-term performance (coulombic efficiency of 100 % and energy efficiency of 70 %).

Work presented at the 25th International Conference on Diamond and Carbon Materials, 7th-11th september 2014, Madrid (Spain), Remarkable progress in the fabrication of carbon nanotube composite fibers has resulted through the development of the wet-spinning technique pioneered by Vigolo et al. [1] This process implies the fabrication of gel fibers as a result of the collapse of surfactant-stabilized carbon nanotube dispersions when injected into a coagulation bath. When dried, those gel fibers become solid fibers with high carbon nanotube contents (³ 50 wt.%), significantly higher than those achieved by other fiber spinning technologies, such as melt-spinning or electrospinning. We here report how this wet-spinning method provides carbon nanotube composite fibers with tunable properties, which mainly depend on the composition of the coagulation bath used. Polymers including polyvinyl alcohol (PVA) [2-5] and polyethylenimine (PEI) [6] have been here investigated as coagulants.[7] Remarkable transport-, supercapacitor- and electrochemical actuation properties are demonstrated for these coagulation wet-spun fibers, that can be woven into fabrics and therefore offer promise for a variety of electronic textile applications [2-4]., This work has been funded by the Fundación Domingo Martínez (Ayuda a la Investigación 2013).