Tailor-made carbon electrodes for redox flow batteries

January 26, 2023

In a new collaboration, TU/e and Schunk Group jointly work on scaling up the manufacturing process of novel carbon-based electrodes while simultaneously investigating how to commercialize the product.

Antoni Forner-Cuenca (left) shows the lab set-up to Hartmut Gross. Photo: Bart van Overbeeke

Redox flow batteries (RFBs) are stationary, industrial-size batteries that are used to store excess electrical energy produced from renewables, such as solar power or wind energy. Providing access to stored energy when it’s dark or windless will accelerate the transition to sustainable energy. A scientific publication about the non-solvent induced phase separation (NIPS) electrodes that were developed by Antoni Forner-Cuenca and his colleagues drew the attention of Schunk Group, an industrial supplier of carbon components, among other things. In early October, they kicked off their collaboration to research and scale up these NIPS electrodes to a commercial scale at TU/e.

It is not uncommon to find research groups at TU/e collaborating with industry to develop techniques and share knowledge. What sets the collaboration between Schunk Group and Antoni Forner-Cuenca’s Electrochemical Materials and Systems Laboratory apart is not just how they share the responsibilities without compromising the scientific independence of the university. It is the fact that the company believes in this new technology enough to fund the entire project, including a PhD researcher for the fundamental research at TU/e. This will speed up the research and development significantly when compared to the more conventional road of applying for and receiving public funding for the research.

That optimism seems to be entirely justified when considering the technology that this collaboration will concern – a new carbon-based electrode material for redox flow batteries (RFB) which leads to smaller stacks (assembly of serial cells) and lower costs per kW in the entire battery unit. The NIPS electrodes were developed in an international collaboration between TU/e and MIT, as was published in Advanced Materials and Cell Reports Physical Science. PhD students Rémy Jacquemond (supervised by Antoni Forner-Cuenca and Kitty Nijmeijer) and Charles Wan (supervised by Fikile Brushett and Yet Ming Chiang) were the leading researchers in this work.

Large-scale energy storage

Storing surplus electrical energy to be used at a later moment is one of the challenges of the energy transition. Among the many solutions being developed, redox flow batteries have long been around and are considered a very promising solution to speed up the energy transition. They are most suited for industrial-scale energy storage because they are fairly large in size and unfeasible to move around during operation, although they fit in conventional shipping containers.

Their power and capacity in modules currently scale up to megawatts (MW) and multiple megawatt hours (MWhs). Inside these batteries, the electrochemical stacks consist of a series of individual cells. Each of them consists of two sheets of carbon material functioning as electrodes. So, a 1 MW battery would probably consist of ten thousand electrodes or more. The demand for greater energy storage is expected to go up to the gigawatt scale soon, with battery sizes scaling accordingly.

Since demand for industrial-size battery solutions will only increase, it is imperative to improve their costs and performance when considering ways to speed up the energy transition, especially in large-scale applications. Currently, multiple flow battery chemistries are being developed with a wide range of options in design and materials used. Time alone will tell which designs will end up being the most reliable, cost-effective and durable solutions.

Photo: iStock / Petmal

Photo: Bart van Overbeeke

Inspiring material

“It is an exciting technology to be working on. Doing fundamental research on redox flow batteries helped us to conceptualize what an ideal electrode would look like. We are thrilled that the prepared NIPS materials in the present work have demonstrated promising performance in flow batteries,” explains Forner-Cuenca. “Besides our passion for fundamental research, we like to make a more tangible impact on society and are eager to see our research in the real market.”

“We were intrigued and amazed by the potential of the NIPS electrodes for doubling the power density compared to the best commercial electrodes available today,” adds Hartmut Gross, Director New Business and Technology at Schunk Group. “However, bringing the NIPS electrode to market means scaling two orders of magnitude in size up to 900 cm² in area – there is still scientific research to be done, especially by adopting the chemistry while implementing the process into industrial equipment. Therefore, we need and benefit from each other.”

NIPS electrodes

Existing commercially available flow battery electrodes are made of carbon fibers. However, these materials are not perfectly matched to the requirements inside the flow batteries. More specifically, it is challenging to allow pathways for the liquid flows and a high surface area for the reactions, combined with a high electrical conductivity, to take place at the same time.

The NIPS electrodes, on the contrary, feature a unique three-dimensional structure that is difficult to attain with existing manufacturing methods. NIPS electrodes can be made as sponges or honeycomb-like structures, which provide very good performance in the flow battery.

“The precise control over the morphology is the key advantage of this method, as we can tailor electrode structure for specific applications. So, this is a flexible synthetic platform. Additionally, the NIPS electrodes have the potential to be cheaper on a large scale in the future,” says Forner-Cuenca.

Pictured is a cross-section of a carbonized NIPS electrode prepared from a polymer solution composed of polyacrylonitrile (PAN: precursor of the carbon scaffold), polyvinylpyrrolidone (PVP: pore forming agent) and dimethylformamide (DMF: solvent). This carbon material is the result of 1050 °C carbonization of the porous PAN film that is obtained after non-solvent induced phase separation. The big finger-like black voids are called ‘macrovoids’. These macrovoids form the typical NIPS electrode honeycomb network.

Photo: Rémy Jacquemond

Left to right in front of the Helix-building on the TU/e campus: Jeremias Schoenfeld, Hartmut Gross, Antoni Forner-Cuenca, Hendrik Hemmelmann, Simona Buzzi. Photo: Bart van Overbeeke


As it turned out, Schunk Group – already a leading supplier of graphite bipolar plates in the market – was very interested in the NIPS electrodes and believes that they will be instrumental in creating the next generation of redox flow batteries.

Gross clarifies this: “This is why we settled on the approach and collaboration that we have now. The PhD researcher at the university will conduct the fundamental research. At the same time, we have hired a dedicated engineer who will work on reproducibility, robustness, production methods and production design, among other things. In short, he will focus on all the aspects that will make the NIPS electrodes a viable product that we can mass produce. Together, this duo will work closely together and share findings, insights and inspiration both ways.”

The PhD researcher, Simona Buzzi, will carry out the research and the first steps of scale-up, while Hendrik Hemmelmann will contribute with co-development work on Schunk’s side. “We have our partners lining up for implementation testing and reliability tests. We trust we can make it work on an industrial scale in less than three to four years and, in that case, we have faith that our funding will be money well-spent in speeding up a technology that would otherwise not have become available for at least another ten years,” concludes Gross.

Schunk Group

The Schunk Group is a global technology company. The company is a leading supplier of products made of high-tech materials – such as carbon, technical ceramics and sintered metal – as well as machines and systems – from environmental simulation and air conditioning to ultrasonic welding and optical machines. The Schunk Group has around 9,000 employees in 27 countries and achieved sales of €1.3 billion in 2021.

Nicole van Overveld
(Science Information Officer)

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