Solid Oxide Electrolysis: right on track towards industrial application

29-11-2021 | P2Hydrogen | Research result

The global sustainability transition has sparked renewed interest in high temperature electrolysis by means of solid oxide cells. A major advantage of these ceramics-like devices is their potential for integration in an industrial process environment at high temperatures. This opens avenues towards efficient production of a range of green chemicals and fuels. Frans van Berkel and Claire Ferchaud are leading the Solid Oxide Electrolysis (SOE) research at VoltaChem/TNO in Petten, where the new Faraday Lab houses state-of-the-art facilities for development and testing of industrially relevant SOE cells and stacks.

Claire Ferchaud is the young and eager researcher, Frans van Berkel more at age and somewhat thoughtful. But both are good-humoured, ambitious and confident to play a leading role in solid-oxide cell technology. A role that is internationally recognized, as could be seen last summer when both presented papers at the 17th International Symposium on Solid Oxide Fuel Cells. This is the preeminent conference on solid oxide cells for fuel cell and electrolysis applications, with a history of over 30 years. As the name of the symposium reflects, the development of solid oxide cell technology stems from the fuel cell era. This is no different at VoltaChem/TNO where research started many years ago in Petten at the Energy Research Centre ECN, a founding VoltaChem partner that merged with TNO in 2018.

Faraday Lab

With the growing relevance of electrolysis technology for generating hydrogen and establishing carbon circularity, the solid oxide cell development efforts were revitalized in 2018 by Van Berkel, Ferchaud, and other researchers from the former fuel cell research group. "Through our collective experience we were able to pick up the thread fairly easily and focus our efforts on Solid Oxide Electrolysis", says Van Berkel. The efforts received a substantial boost when the Dutch Ministry of Economic Affairs and Climate (EZK) granted 6 M€ to invest in state-of-the-art research facilities in electrochemistry and green hydrogen production. After some delays because of the COVID-19 pandemic, the SOE efforts in the new Faraday Lab are in full swing since November 2020. The team now involves five researchers on the core Solid Oxide Cell development activities, supported by TNO engineering departments and workshops (Delft, Rijswijk, Eindhoven). According to Ferchaud and Van Berkel, the VoltaChem/TNO efforts in SOE are now on par with the best laboratories worldwide. "It's safe to say that we have regained our position as an international center of expertise in solid oxide cell technology", Ferchaud says. "This has already resulted in many collaborations with European and national academia and industry. So we are in a good position to help take SOE to the next level. In doing so we deal with the most pressing issues: lifetime, scale-up, and of course cost reduction of the cell, the stack, and the full system."

Improving materials and cell microstructures 

Even though commercial suppliers such as Haldor Topsoe (Denmark) and Sunfire (Germany) are already planning systems at megawatt scale, for current state-of-the-art technology the ballpark figure in lifetime is some 20.000-40.000 hours. "That has to be cranked up to at least 60.000 hours to bring SOE to industrial relevance on a large scale", Van Berkel says. "We have developed test equipment and procedures for electrochemical testing of SOE cells under the relevant conditions for industrial operation. This means flexibility in feed gas compositions, flow rates and operating temperatures - up to 900 degrees." These systems help to evaluate the team's efforts in improving materials and cell microstructures to arrive at more robust cells. But they can also cater to the needs of industrial parties who want to test their cells and stacks.

     

Where current industrial technology uses cells of around 15x15 cm², the VoltaChem/TNO team has laid out a solid oxide cell manufacturing line to arrive at 30x30 cm² cells. "The SOE technology we have developed here in Petten delivers a complete integrated and stackable cell containing a membrane, electrodes and porous transport layers", Van Berkel explains. "We have already demonstrated that at 10x10 cm² scale. Enlarging the active area by an order of magnitude constitutes the next step in solid oxide electrolyzers, reducing cost, boosting efficiencies and thus further increasing their industrial relevance." Testing equipment is being developed to be able to evaluate electrolysis performance at this scale from 2022 onwards. The established solid oxide cell manufacturing line in Petten supports industrial partners to establish a commercially viable solid oxide cell product and production line. The challenge would be to automate the manufacturing process, incorporating the knowledge and 'fingerspitzengefühl' of the Petten operators, says van Berkel. He adds that VoltaChem/TNO will be teaming up with industrial partners, for reasons of both expertise and investment power.

Green fuels and chemicals

While improving the technology, the team is also focusing on future application. As Ferchaud puts it: "Enhancing lifetime and scaling up will remain important. But to really get this technology off the ground, we need to demonstrate its potential for industry integration." The high operating temperatures of SOE systems enable integration with many industrial processes and the use of residual heat will boost operational efficiency. The team is for instance exploring possibilities for large-scale high-temperature steam electrolysis for hydrogen generation in existing industrial infrastructures such as refineries or ammonia plants. Another approach lies in high-temperature CO₂- electrolysis as well as co-electrolysis of steam and CO₂. These enable industrial CO₂ re-use and provide a route to green fuels and chemicals. As a demonstration case, a techno-economic analysis was made for methanol synthesis where SOE is used for co-electrolysis of CO₂ and steam, yielding a green 'syngas' as the source for methanol production using conventional technology. "Such an analysis provides an exercise in systems design and an outlook on feasibility", Van Berkel says. "We calculate a production cost for SOE-based methanol synthesis of less than 700 €/ton, which in our eyes is an indication of feasibility." And of course, methanol is a pars-pro-toto and many other options are being considered, among them green kerosine for aviation purposes. "We believe SOE technology can be meaningful in many applications", says Ferchaud. "However, we're not claiming to have the ultimate technology here. Each technology has its advantages and in view of the huge challenges of the transition there will be more than enough opportunities many different systems to play their part, complementing each other." 

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Publication references SOFC XVII:

C. J. Ferchaud, F. Berkel, L. Berkeveld, M. Heijink-Smith, J. Veldhuis, H. van Wees, Use Co- and Ni-Free Air Electrode in Solid Oxide Cell Manufacturing for Electrolysis and Fuel Cell Applications; 

F. Berkel, C. J. Ferchaud, O. Partenie, M. Linders, Y. van Delft Solid Oxide Cell Technology Development at TNO, ECS Transactions, 103 (1) 591-602 (2021)

 

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