Publications | MeBattery

2025

Raman spectroelectrochemistry for operando characterization of redox flow batteries
Lara Lubian, Rubén Rubio-Presa, Virginia Ruiz, Alvaro Colina, Edgar Ventosa
Advanced in-situ and time-resolved techniques play a critical role to improve performance of Aqueous Organic Redox Flow Batterie (AORFBs). In this publication, the development and implementation of operando Raman spectroscopy is shown for dihydroxyanthraquinone–ferrocyanide alkaline flow battery.
Thermodynamic strategies to increase solubility for higher energy density in organic redox flow batteries
Murilo L. Alcantara, Dinis O. Abranches, Catarina M.S.S. Neves, Rubén Rubio-Presa, Edgar Ventosa, João A.P. Coutinho
Improving the solubility of redox-active organic molecules (ROMs) in electrolyte solutions is vital for boosting the energy density of redox flow batteries and avoiding precipitation issues. This study explores six thermodynamic strategies to enhance ROM solubility by lowering melting points or activity coefficients.
Enhancing the Stability of Aqueous Membrane-Free Flow Batteries: Insights into Interphase Processes
Paula Navalpotro, Carla Santana Santos, Murilo L. Alcantara, Vanesa Muñoz-Perales, Santiago E. Ibañez, Antonio Martínez-Bejarano, Nomnotho Jiyane, Catarina M. S. S. Neves, Rubén Rubio-Presa, Thomas Quast, Wolfgang Schuhmann, João A. P. Coutinho, Rebeca Marcilla
This study presents a new aqueous membrane-free flow battery based on a novel aqueous biphasic system with enhanced electrolyte properties. The system uses compatible species exhibiting high partitioning behavior, as demonstrated by computational and experimental analysis. These species prevent parasitic reactions, enabling unprecedented studies of the liquid–liquid interphase and providing valuable insights into advancing this battery technology.
Membrane-free redox flow battery: From the idea to the market
Paula Navalpotro; Jesus Palma; Vanesa Muñoz-Perales; Antonio Martínez-Bejarano; María Victoria Martín-Arroyo; David P. Taylor; Anetta Platek-Mielczarek; Pier Giuseppe Rivano; Federico Paratore; Emilio Dal Re; Rebeca Marcilla
Due to their efficiency and ability to decouple energy and power density, redox flow batteries (RFBs) are particularly suited to address the rising energy demand and the need for effective energy storage systems. Still, the costs for ion-selective membranes and vanadium-based electrolytes used for those batteries are high. This publication considers and alternative membrane-free flow battery technology that relies on immiscible electrolytes which separate into two distinct liquid phases without the use of a membrane.
Efficient Confinement of Solid Capacity Booster Powder as Monolithic Structures for High Performance Redox Mediated Flow Batteries
Gimena Marin-Tajadura, Yi He, Virginia Ruiz, Edgar Ventosa
Confinement of solid electroactive materials in the external reservoirs of Redox-Mediated Flow Batteries (RMFB) is of critical importance for the development of this family of battery technologies. Herein, an efficient strategy that is based on a flow-through configuration is proposed.
On the Relevance of Static Cells for Fast Scale-Up of New Redox Flow Battery Chemistries
Lara Lubian, Ruben Rubio-Presa, Roberto, Sanz, Virginia Ruiz, Edgar Ventosa
The search for organic electroactive molecules suitable in aqueous organic flow batteries requires great efforts not only from an electrochemical perspective but also from an organic synthesis viewpoint. In this work, the relevance of static cells for accelerating the search and helping understand degradation mechanisms is focused on.
New non-invasive method to monitor and reverse faradaic imbalance in redox flow batteries
Miguel Cantera, Koray Cavusoglu, Lara Lubián, Rubén Rubio-Presa, Roberto Sanz, Virginia Ruiz, Jose María Cámara, Edgar Ventosa
State-of-health monitoring is key for the correct operation of redox flow batteries, which are affected by parasite reactions like Faradaic imbalance. This work proposes a new non-invasive monitoring method based on the minimum derivative of the cell voltage, used as the input that controls a rebalancing device to recover the capacity loss, extending the battery lifetime.

2024

Recessed microelectrodes as a platform to investigate the intrinsic redox process of Prussian Blue analogs for energy storage application
Nomnotho Jiyane, Carla Santana Santos, Igor Echevarria Poza, Mario Palacios Corella, Muhammad Adib Abdillah Mahbub, Gimena Marin-Tajadura, Thomas Quast, Maria Ibáñez, Edgar Ventosa,Wolfgang Schuhmann
The determination of the intrinsic properties of solid active material candidates is essential for their performance optimization. However, macroscopic electrodes and related analytical techniques show challenges concerning the number of additionally influencing parameters. We explore recessed microelectrodes (rME) as a platform that allows for a binder-free investigation of Prussian Blue analogues (PBA), a family of promising battery materials.
Insights of the Proton Transport Efficiency of a Membrane Electrode Assembly by Operando Monitoring of the Local Proton Concentration during Water Oxidation
Rajini P. Antony, Lejing Li, Carla Santana Santos, Ndrina Limani, Stefan Dieckhöfer, Thomas Quast, Jonas Weidner, Wolfgang Schuhmann
The authors present a novel scanning electrochemical microscopy approach to measure local pH near a working MEA in zero-gap electrolyzers, offering insights into proton transport efficiency, the effects of activation, electrolyte buffering, and poisoning, all crucial for optimising sustainable fuel production.
Controlling surface wetting in high-alkaline electrolytes for single facet Pt oxygen evolution electrocatalytic activity mapping by scanning electrochemical cell microscopy
Geovane Arruda de Oliveira, Moonjoo Kim, Carla Santana Santos, Ndrina Limani, Taek Dong Chung, Emmanuel Batsa Tetteh, Wolfgang Schuhmann
Scanning electrochemical cell microscopy (SECCM) has been used to explore structure-electrocatalytic activity relationships through high-resolution mapping of local activities of electrocatalysts. However, utilizing SECCM in strongly alkaline conditions presents a significant challenge due to the high wettability of the alkaline electrolyte leading to a substantial instability of the droplet in contact with the sample surface, and hence to unpredictable wetting and spreading of the electrolyte.
Nanoelectrochemical Platform for Elucidating the Reaction between a Solid Active Material and a Dissolved Redox Species for Mediated Redox-Flow Batteries
Dr. Carla Santana Santos, Dr. Thomas Quast, Prof. Edgar Ventosa, Prof. Wolfgang Schuhmann
We demonstrate a nanoelectrochemical methodology to monitor the reaction between the dissolved species in solution and the solid active material electrodeposited in recessed carbon nanoelectrodes. Our strategy overcomes issues inherent to standard methodologies, such as mass transport limitation, and evaluation of the intrinsic reactivity of the solid material.
Membrane-free Zn hybrid redox flow battery using water-in-salt aqueous biphasic electrolytes
Sirugaloor Thangavel Senthilkumar, Santiago E. Ibañez, Paula Navalpotro, Eduardo Pedraza, Nagaraj Patil, Jesus Palma, Rebeca Marcilla
In this study, we develop a membrane-free Zn hybrid redox flow battery (RFB) using an unconventional water-in-salt aqueous biphasic system (WIS-ABS). This membrane-free Zn hybrid battery employs soluble ferrocene (Fc) derivative and Zn salt as the active species in the immiscible catholyte and anolyte, respectively.
Anodic H2O2 Generation in Carbonate-Based Electrolytes—Mechanistic Insight from Scanning Electrochemical Microscopy
Dr. Lejing Li, Dr. Rajini P. Antony, Dr. Carla Santana Santos, Dr. Ndrina Limani, Dr. Stefan Dieckhöfer, Prof. Dr. Wolfgang Schuhmann
For the anodic H2O2 generation, it has been shown that the electrolyte composition can steer the reaction pathway toward increased H2O2 generation. For this study, local pH measurements were performed using a Au nanoelectrode positioned in close proximity to an operating anode by shear-force scanning electrochemical microscopy (SECM).
Investigation of Doping Effects on the Local Electrochemical Activity of Transition Metal Dichalcogenides 2D Materials
Walner Costa Silva, Moonjoo Kim, Geovane Arruda de Oliveira, Leandro Vitor da Silva, Emmanuel Batsa Tetteh, Cynthia Marina Rivaldo Gomez, Wellerson dos Reis Ramos, Benjamin Fragneaud, Wolfgang Schuhmann, Carla Santana Santos, Daniel Grasseschi
Finding strategies to enhance catalysts’ electrochemical activity is based on controlling the material design. Bidimensional materials (2DM) such as MoS2 are explored as catalysts for the hydrogen evolution reaction (HER). A comprehensive study of the effects of doping 2D materials with transition metals based on theoretical predictions in tandem with experimental investigation correlates the doping type to the changes in the electronic and electrochemical activity.
An Automatized Rebalancing System to Address Faradaic Imbalance and Prolong Cycle Life in Alkaline Ferrocyanide – Anthraquinone Redox Flow Batteries
Miguel Cantera, Lara Lubián, Koray Cavusoglu, Rubén Rubio-Presa, Prof. Roberto Sanz, Virginia Ruiz, Prof. Jose María Cámara, Prof. Edgar Ventosa
Faradaic imbalance is one of the factors that shortens lifetime of aqueous organic redox flow batteries by reducing its capacity. This work proposes an automatized system based on a rebalancing device located in an external reactor. The system is able to recover the capacity and maintain it during 800 cycles.
Au Micro- and Nanoelectrodes as Local Voltammetric pH Sensors During Oxygen Evolution at Electrocatalyst-Modified Electrodes
Lejing Li, Ndrina Limani, Rajini P Antony, Stefan Dieckhöfer, Carla Santana Santos, Wolfgang Schuhmann
The scarcity of state-of-the-art oxygen evolution reaction (OER) electrocatalysts has led to intensive research on alternative viable electrocatalytic materials. While activity and cost are the main factors to be sought after, the catalyst stability under harsh acidic conditions is equally crucial.

2023

Broadening Applicability of the Poor Academic's Method for Reversing Polarity in Redox Flow Cell Cycling
Gimena Marin-Tajadura, Eduardo Sánchez-Díez, Virginia Ruiz, Edgar Ventosa
The use of symmetrical cells is becoming popular for the search of new electroactive materials in redox flow batteries. Unfortunately, low-cost battery cyclers, commonly used for electrochemical battery testing, are not compatible with symmetrical cells since they usually cannot apply negative bias voltages needed for symmetrical cells. The insertion of a Ni−Cd battery in the voltage sensing path is a simple and effective methodology to overcome this limitation for certain battery cyclers.
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).
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.
On the Tunability of Toxicity for Viologen-Derivatives as Anolyte for Neutral Aqueous Organic Redox Flow Batteries
Sandra de la Parra, Juan Antonio Tamayo-Ramos, Rubén Rubio-Presa, Daniel Perez-Antolin, Virginia Ruiz, Prof. Roberto Sanz, Carlos Rumbo, Prof. Edgar Ventosa
Viologen-derivatives are the most widely used redox organic molecules for neutral pH negative electrolyte of redox flow batteries. However, the long-established toxicity of the herbicide methyl-viologen raises concern for deployment of viologen-derivatives at large scale in flow batteries. Herein, we demonstrate the radically different cytotoxicity and toxicology of a series of viologen-derivatives in in vitro assays using model organisms representative of human and environmental exposure, namely human lung carcinoma epithelial cell line (A549) and the yeast Saccharomyces cerevisiae.
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.
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.
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.