Newsletter 08/22

Word from the coordinators

Dear readers,

After a long period of COVID-induced online meetings and virtual conferences, the SONAR-team used the spring and the regained possibilities to promote SONAR-topics and increase the visibility of the project in several conferences to both the scientific community and the general public. Members of SONAR attended many different events around the world and will continue to do so.

Apart from the refreshing social and academic exchange, the SONAR members also strive to make the best use of the project results. For this purpose, we held an exclusive workshop with the members of our Industrial Exploitation Board (IEB), but also another one together with the sister -Project COMPBAT. We carried out a joint COMPBAT/SONAR workshop, including a panel discussion immediately before the International Flow Battery Forum (IFBF). The workshop was well attended by delegates from several companies and from academia. One goal of the workshop was to get feedback from the industry on how to align our developments as effectively as possible to real world’s demands and how to use the results beyond the project duration. At this point, many thanks to all participants and their valuable tips! Some work packages have already taken up the suggestions and integrated them into the ongoing developments.

We wish all readers a hopefully continued successful and healthy 2022!

Carolyn Fisher & Jens Noack
(Project manager & Project coordinator)

SONAR inside

Team News


On June 15, 2022, the 6th General Assembly of our project was held in Amiens, France at the Laboratoire de Réactivité et Chimie des Solides (LRCS). The special thing about this meeting this time was that the participants had decided to hold a physical meeting, whereby it was the first General Assembly at all after the Kick-Off Meeting 2020 in person.

During the one-day meeting, the results of the individual work packages were presented, as well as the way forward in SONAR was discussed. Furthermore, the participants had the opportunity to visit the premises of the LRCS.

Congratulations and farewell to Dr. Rocco Fornari, who was working on the atomistic simulations and successfully finished his PhD at DTU and a cordial welcome to Dr. Xiaotong Zhang, who started as a Postdoc to continue the activities in the SONAR project.

SONAR outside

Here is a full list of events attended to so far and some impressions from those meetings:

18th Symposium on Modelling and Experimental Validation of Electrochemical Energy Technologies

© Roman Schaerer

In March, the ModVal was held at Schloss Hohenkammer, Germany. Among the participants and as speakers were Dr. Roman Schärer from the University of Applied Sciences Zurich and AA/Prof. Dr. Jens Noack (Fraunhofer ICT / University New South Wales), project coordinator. Roman presented a poster on the results obtained in the field of 0D modelling of redox flow batteries and Jens gave an overview talk on the results obtained so far in SONAR.

ModVal is one of the most important conferences on modelling and simulation of electrochemical devices. This year's conference was held with over 200 attendees from all over the world despite the severe constraints of the COVID pandemic.

Smart Energy Conference and Exhibition together with CENELEST

© Chris Menictas

4 – 5th May 2022, ICC Sydney, Australia,

SMART Energy is one of the largest renewable energy events in Australia. SONAR participated this year with a booth shared with CENELEST at the fair.

Among other things, a technology demonstrator for the High-Throughput screening process was represented. The software for the search for new active materials for aqueous organic redox flow batteries could be tested on a laptop. In addition, materials of cells, electrodes and a small demonstration redox flow battery were shown. The booth was supervised especially with the support of UNSW students from UNSW Challenge program NextGEN.

Science Night

© Michael Krapp

Over two days in May, school classes and interested citizens were able to learn about the current state of research in the Bonn region in Germany. To explain the screening process under development, Fraunhofer SCAI challenged visitors to find the best combination of active materials to build a complete redox flow battery cell. In general, the topic of energy storage and in particular flow batteries received a lot of attention and encouragement.

31st Topical Meeting of the International Society of Electrochemistry

© Jens Noack, Astrid Maaß

The ISE-31 Meeting took place in Aachen, Germany from May 15 – 19, 2022. Among the participants and as presenters were Dr. Astrid Maaß (Fraunhofer SCAI) and AA/Prof. Dr. Jens Noack (Fraunhofer ICT / University of New South Wales), project coordinator. Astrid presented results from High-Throughput Screening to find new organic active materials for redox flow batteries during a talk and Jens gave an overview talk on the results achieved so far in SONAR.

The International Society of Electrochemistry is one of the two leading electrochemical societies worldwide and organizes different conferences in the field of electrochemistry every year. The 31st ISE Topical Meeting was attended by over 150 participants from various countries.

241st Meeting of The Electrochemical Society

© Jens Noack

Daniel Gerlach, Prof. Dr. Piotr de Silva and AA/Prof. Dr.-Ing. Jens Noack attended this year’s 241st spring meeting of the Electrochemical Society in Vancouver, Canada in May. Together, they gave two keynote lectures, three additional lectures and chaired two sessions in the area of redox flow batteries and computational electrochemistry.

32nd Topical Meeting of the International Society of Electrochemistry

© Jens Noack

The ISE-32 Meeting of the International Society of Electrochemistry on the topic "Experimental and Modelling Tools for Electrochemical Energy Devices" took place in Stockholm, Sweden from June 20 – 22, 2022. Among the participants and as an invited speaker was also AA/Prof. Dr. Jens Noack, with a presentation of the results achieved so far in the project.

The International Society of Electrochemistry is one of the two leading electrochemical societies worldwide and organizes different conferences in the field of electrochemistry every year. The 32nd ISE Topical Meeting was attended by several hundred participants from all over the world.

International Flow Battery Forum 2022

© Jens Noack
© Jens Noack

From June 28 – 30, the annual International Flow Battery Forum (IFBF) took place in Brussels, Belgium. SONAR was represented by several participants with posters and a presentation. Results from the project and standardization of redox flow batteries were reported.

In addition, SONAR organized a joint workshop with its sister project COMPBAT on the topic of "Modelling and Simulation" before the actual program of the IFBF began.

SONAR was further represented together with FLORES, the European network of EU projects on redox flow batteries, at a booth in the exhibitors' area. Participants of the IFBF made extensive use of the opportunities to obtain information and to exchange experiences. This year, IFBF had nearly 300 participants from a variety of countries around the world.

SONAR Insights

Take a quick look at some of our recent developments:

High-volume pre-selection of active materials: work behind the scenes

Astrid Maaß, Fraunhofer SCAI, Germany

Our aim is to provide a tool chain for the rapid selection of promising RFB systems. To this end, we have created a basic workflow with trained mathematical models that already demonstrates the power of the approach.

The screening proceeds through the steps of generating reduced species, evaluating the synthetic accessibility of a redox couple, their individual solubilities, and half-cell potential.  At each stage, compounds that do not meet the desired properties can be removed. The remaining candidate pairs are finally recombined into complete cells that can be tested for their open-circuit voltage, limiting solubility, or even maximum power density - the resulting output can be used as a direct input to ZHAW's 0D cell model, which can be embedded in the overall procedure.

A prototype version is already available as a web application (, but work continues to provide software that is more flexible or easily extensible and supports some logic.

To complement this fast but fixed sequence, a second framework based on AIIDA and NWChem has been made available to perform automated QM calculations. As a first step, we will use this facility to pre-calculate training data. Later, it will be linked to the screening workflow mentioned above, which can pass redox pairs in doubt to the QM calculation to determine the half-cell potential. In this way, the quality of our predictions would never fall below the level of accuracy that can be achieved by first-principles methods.

Work on Parameter Identification for a Reduced Electrochemical Interface Model

Roman Schaerer, ZHAW, Switzerland

The chemical and physical processes at the electrochemical interface between the solid electrode and liquid electrolyte are of major importance as they can impact the performance and life time of a redox flow battery. High-fidelity atomistic simulations, such as DFT and KMC, can be used to resolve the coupled processes at the interface in detail. However, their high computational cost prohibits extensive parameter and sensitivity studies.

The University of Applied Sciences Zurich (ZHAW), Switzerland, is investigating a reduced continuum-based model for the electrochemical interface, which allows for fast model evaluations, while capturing important processes, such as adsorption of electrolyte species to the solid electrode and charging of the double layer. The considered thermodynamics-based continuum model has been developed in a series of publications by Dreyer, Landstorfer, Guhlke, and Müller. The proposed description of the double layer is based on a coupled system of a modified Nernst-Planck and momentum balance law. In contrast to other works, the model does not assume a specific structure of the double layer in terms of a compact and diffuse layer. Instead, the balance equations give rise to the formation of a double layer structure that depends on the boundary conditions.

The reduced model depends on variety of physical parameters, such as the susceptibility of the electrolyte in the vicinity of the electrode or the molar volumes and solvation shell numbers of the ionic species. These parameters must be inferred either by experimental measurements or lower-scaled atomistic simulations. To facilitate a robust parameter identification, ZHAW is investigating parameter estimation methods, such as the Bayesian inference based on MCMC sampling strategies.

Pore scale resolved continuum model for cell performance

Amadeus Wolf, KIT, Germany

Governing equations of the CFD half-cell model based on Finite Volume Method and with coupled fluid and solid regions. Simulation of laminar electrolyte flow and coupled charge conservation within both regions including electrochemical reaction on a digital twin of the real electrode.
Illustration of the discharge process in the positive half-cell compartment of an organic TEMPO-based RFB system (normalized quantities). Velocity profile (arrows) of the electrolyte flow coming from the bottom to the top. Quasi steady-state TEMPO+ concentration profile within the electrolyte.

Three-dimensional pore-scale continuum models resolve the real geometry of the electrode to gain insight of the microstructural processes inside the flow battery. They offer great capability to obtain information about the microstructure and how it affects transport processes within the electrode and the overall cell performance.

Most of the flow battery modelling approaches to date have concentrated on volume-averaged or macroscopic calculation of transport processes within porous electrodes captured by using empirical relations e.g. Darcy’s law or Bruggeman correction. Hence, the behaviour of key parameters like ionic diffusivity or permeability on performance is not represented correctly, as well as the coupled species and charge transport. Pore-scale resolved models overcome these disadvantages and provide spatial characteristics of velocity, concentration or current density depending on the complex structures of the electrode. Therefore, a spatially resolved continuum model is set up to gain insight into the micro-structural processes inside the flow battery.

The three-dimensional half-cell model is parameterized with the known model chemistry of the organic 4-OH-TEMPO system and accounts for electrolyte flow, mass and charge transport. The electrochemical reaction is implemented using Butler-Volmer type kinetics to couple the solid and electrolyte region. The simulations consider galvanostatic and isothermal operating conditions comprising laminar and steady-state flow. The governing equations for the electrolyte, solid and interface region are shown in Figure 1.

Simplified structured electrodes are used as computational domain to numerically investigate the influence of the initial active material concentration, the current density and the active surface. Furthermore, a digital twin of the real electrode microstructure is generated by experimental image reconstruction from X-ray computed micro-tomography and used to investigate the impact of different flow rates on the concentration distribution within the electrolyte and on the half-cell potential. Figure 2 shows an illustration of the half-cell digital twin during discharge colored by normalized TEMPO+ concentration including arrows characterizing the fluid flow.

SONAR outlook

Meet SONAR members at:

September 12th, 2022
FLORES workshop on digital twins and LCA for flow batteries

September 12 – 16, 2022

ISE – 73rd Annual Meeting: Electrochemistry-Powering a Healthier Planet
September 20 – 22, 2022
Düsseldorf, Germany
Expo for Decarbonized Industries (former Energy Storage) + IRES conference by EUROSOLAR
September 27 – 30, 2022
Berlin, Germany
Electrochemistry 2022: At the Interface between Chemistry and Physics
October 9 – 13, 2022
Atlanta, Georgia, USA
ECS – 242nd ECS Meeting
October 12 – 14, 2022
hybrid: Online + Presence, Birmingham, UK
2nd World Energy Storage Conference (WESC 2022), jointly with the 7th UK Energy Storage Conference (UKESC 2022)
October 26 – 28, 2022
Chalmers University of Technology, Gothenburg, Sweden



November 27 – 30, 2022
Santiago, Chile
ISE – 33rd Topical Meeting of the International Society of Electrochemistry: Challenges in Molecular Electrochemistry and Surface Reactivity