Most routes to e-fuels start the same way: renewable electricity splits water, and the resulting green hydrogen is then combined with recycled CO₂ in a separate synthesis step. Researchers at Technische Universität Berlin want to shorten that chain. In two new projects, they aim to convert CO₂ and water directly into ethylene – a building block for synthetic jet fuel – and into carbon monoxide, inside a single electrochemical cell. Funding for TU Berlin totals around €2.6 million over three years. The aviation project is led by Siemens Energy, a SPIN member through Siemens Energy (Schweiz) AG.

What “without hydrogen” really means

In a conventional Power-to-Liquid plant, hydrogen is produced in an electrolyser, compressed, often buffered, and only then reacted with CO₂ in a synthesis reactor. In direct CO₂ electrolysis, CO₂ is reduced at the cathode while water supplies the hydrogen atoms in the very same cell. The hydrogen still ends up in the product – ethylene is C₂H₄, after all – but there is no separate hydrogen plant, no hydrogen storage and no downstream CO₂ synthesis step in between. According to Prof. Peter Strasser, who heads TU Berlin’s Department of Technical Electrochemistry and Electrocatalysis, the key reactions already work in the laboratory. The task now is to make the electrolysers more efficient, longer-lasting and larger.

JEThylen: from CO₂ to ethylene to jet fuel

The JEThylen project focuses on converting CO₂ electrochemically into ethylene. Ethylene is one of the most important base chemicals of the chemical industry, and it can serve as the starting point for synthetic aviation fuel: in a downstream process, the molecules are linked into longer hydrocarbon chains and then refined into jet fuel. The researchers see the advantage in a comparatively short process chain at relatively low temperatures, which should raise overall energy efficiency.

Siemens Energy coordinates the consortium. The partners are TU Berlin, the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB, and the aviation think tank Bauhaus Luftfahrt. The project is funded by Germany’s Federal Ministry of Research, Technology and Space (BMFTR) under its DISCO₂ programme for disruptive approaches to the industrial use of CO₂. It runs from March 2026 to February 2029; TU Berlin’s share is around €1 million. The targets are ambitious:

  • Cell voltage: down from about 4.5 V today to around 2.5 V.
  • Energy efficiency: up from about 27 per cent to 50 per cent.
  • Durability: stable operation for at least 1,000 hours.
  • Scale: from typical laboratory electrodes of around 10 cm² to cells of several hundred cm² in a technical-scale plant, plus concepts for industrial electrodes of up to 0.5 m² (5,000 cm²).

INNOCELL: keeping the electrodes dry

The second project, INNOCELL, tackles a more general problem: how to design CO₂ electrolysis cells that remain powerful and stable at larger scale. It builds on a cell design developed and patented at TU Berlin for gas diffusion electrodes, which feed gaseous CO₂ directly to the catalyst and thus allow high current densities. Their weak spot is “flooding”: liquid electrolyte seeps into the pores, blocks the gas supply and severely disrupts the process. INNOCELL uses water-repellent, electrically insulating polymer substrates to keep the electrodes dry, combined with a specially developed current collector for electrical contact.

The cells will be tested at 60 to 80 °C and up to 30 bar – conditions relevant for industrial CO₂ electrolysers. The targets are current densities of at least 500 mA/cm², an energy efficiency of at least 45 per cent and at least 1,000 operating hours. Besides ethylene, INNOCELL also looks at carbon monoxide. CO is a key intermediate of the chemical industry and a component of synthesis gas, from which methanol and other synthetic fuels can be made. Which product is taken forward to larger scale will depend on the performance achieved. The project runs from 2026 to 2029 under the German federal research ministry’s VIP+ programme, with €1.6 million for TU Berlin.

A reality check

  • Efficiency: Today’s 27 per cent means that almost three quarters of the electricity is lost as heat. Even the 50 per cent target is not directly comparable with a water electrolyser alone. The fair comparison is the entire chain – water electrolysis plus CO₂ synthesis plus upgrading – against direct electrolysis plus upgrading. That comparison will only be possible once both routes are measured at similar scale.
  • Durability: 1,000 hours is roughly six weeks of continuous operation. Commercial water electrolysers are designed for tens of thousands of hours.
  • Scale: Moving from 10 cm² to several hundred cm² is a big step for a research project. Even the 0.5 m² concept, however, describes a single cell – an industrial e-SAF plant would need many stacks of them.
  • Known hurdles: Across the research field, CO₂ electrolysis has to deal with part of the CO₂ reacting to carbonate instead of product, and with ethylene leaving the cell mixed with by-products and unreacted CO₂, which then have to be separated. The published targets do not yet say how far these issues will be addressed.
  • Technology readiness: In our assessment, both projects move the technology from the laboratory towards technical-scale validation, i.e. from around TRL 3–4 towards TRL 4–5. Industrial plants are not expected before the 2030s.

Why it matters for Switzerland

Demand for e-SAF is set by regulation: the synthetic-fuel sub-quota of ReFuelEU Aviation starts in 2030, and Switzerland has adopted the EU rules. Most of that e-SAF will be imported, so production cost abroad is what counts. Process routes with fewer steps could make plants simpler and cheaper – and potentially small enough to sit directly next to a CO₂ source. In Switzerland, that means the around 30 waste-to-energy plants and the cement works, which will continue to emit unavoidable CO₂ for decades. Turning that CO₂ into ethylene or synthesis gas on site, instead of transporting it, is an attractive idea – provided the electricity is renewable and affordable. At today’s efficiency, direct CO₂ electrolysis is very power-hungry; it makes climate sense only with renewable energy and recycled CO₂.

Swiss research is working on the same molecule. SPIN member Empa is advancing the electrochemical route from recycled CO₂ to ethylene in the EU project REACT, which we covered in July. And for Siemens Energy, which is preparing to rebrand as Omterra, JEThylen adds a CO₂-based option next to its established water electrolysers.

Conclusion

Direct CO₂ electrolysis will not replace the established hydrogen route to e-fuels any time soon. But the TU Berlin projects address exactly the right questions – cell voltage, efficiency, durability and scale – with an industrial partner on board and clear, measurable targets. If JEThylen and INNOCELL reach them by 2029, the technology will have taken a credible step out of the laboratory. For the Swiss Power-to-X community, it is worth following closely: a shorter path from recycled CO₂ to aviation fuel would make defossilisation of flying cheaper – and that is what the e-SAF market needs most.

Source: chemie.de, “CO₂ direkt in Kraftstoffe und Chemikalien umwandeln” (19 October 2026), based on information from TU Berlin.

🤖 AI transparency: This text and its visual were created using AI, reviewed and approved by a human.