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  • Unprecedented Aqueous Solubility of TEMPO and its Application as High Capacity Catholyte for Aqueous Organic Redox Flow Batteries

    Eduardo Pedraza, Carlos de la Cruz, Andreas Mavrandonakis, Edgar Ventosa, Rubén Rubio-Presa, Roberto Sanz, Sirugaloor Thangavel Senthilkumar, Paula Navalpotro, Rebeca Marcilla
    Despite the excellent electrochemical properties of non-functionalized 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), its use in aqueous organic redox flow battery (AORFB) is hindered to date due to its insolubility in water. However, in this study, an unprecedented solubility of 5.6 m is demonstrated in an aqueous solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), which is 80 times higher than in water (0.07 m). A computational study reveals that the unique interaction between TEMPO and TFSI is essential to achieve this record solubility.
  • Computer-Aided Design of Membrane-Free Batteries Using Conductor-like Screening Model for Real Solvents

    José Pedro Wojeicchowski, Catarina S. Neves, Paula Navalpotro, Rubén Rubio-Presa, Edgar Ventosa, Rebeca Marcilla, Joao A.P. Coutinho
    Redox Flow Batteries (RFBs), particularly Membrane-Free Flow Batteries based on Aqueous Biphasic Systems (ABSs), are a promising technology for stationary energy storage. However, to prevent the crossover of species, the redox-active compounds used in the catholyte and anolyte must be selectively dissolved, which is currently achieved using expensive physical barriers. In this study, an approach was developed to predict the partition coefficient of redox-active compounds in ABSs formed by ionic liquids or polymers, salt, and water using the Conductor-like Screening Model for Real Solvents (COSMO-RS).
  • Operando Scanning Electrochemical Probe Microscopy during Electrocatalysis

    Carla Santana Santos, Bright Nsolebna Jaato, Ignacio Sanjuán, Wolfgang Schuhmann, and Corina Andronescu
    This review focused in the recent progress in operando scanning electrochemical probe microscopy (SEPM) measurements during electrocatalysis. SEPM techniques can disclose the local electrochemical reactivity of interfaces in single-entity and sub-entity studies. The powerful operando SEPM measurements can correlate electrochemical activity with changes in surface properties as well as provide insight into reaction mechanisms. The capabilities of SEPMs are showcased toward toward the reduction and evolution of O2 and H2 and electrochemical conversion of CO2. Emphasis is given to scanning electrochemical microscopy (SECM), scanning ion conductance microscopy (SICM), electrochemical scanning tunneling microscopy (EC-STM), and scanning electrochemical cell microscopy (SECCM).
  • A neutral pH aqueous biphasic system applied to both static and flow membrane-free battery

    Paula Navalpotro, Santiago E. Ibañez, Eduardo Pedraza, Rebeca Marcilla
    In this contribution to the Energy Storage Materials journal new aqueous biphasic electrolytes with near neutral pH and low cost are prepared. Battery performance shows high efficiency, capacity utilization and stability. Thus, this manuscript represents a breakthrough in the membrane-free battery since it ceases to just be a promising idea demonstrated only in static conditions and becomes a real flow battery.
  • Addressing Practical Use of Viologen-Derivatives in Redox Flow Batteries through Molecular Engineering

    Ruben Rubio-Presa, Lara Lubian, Mario Borlaf, Edgar Ventosa, Roberto Sanz
    In practical scenarios, viologen-derivatives face an accelerated degradation in the unavoidable presence of traces of oxygen in large-scale redox flow batteries. Herein, we confirm the primary degradation mechanism and propose a straightforward, cheap, and fast method to evaluate the stability of viologen-derivatives toward this degradation. A new viologen-derivative is designed and synthesized to illustrate how molecular engineering can be used to improve stability.
  • A Systematic Study on the Redox Potentials of Phenazine-derivatives in Aqueous Media: A Combined Computational and Experimental Work

    Carlos de la Cruz, Roberto Sanz, Anisley Suárez, Edgar Ventosa, Rebeca Marcilla, Andreas Mavrandonakis
    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.