1. Why is hydrogen considered a pillar of the energy transition?

Hydrogen has become a key vector for decarbonizing sectors where direct electrification is not viable, such as heavy industry or maritime and air transport. It allows us to store renewable energy on a large scale and use it when needed, providing stability to the energy system.
Electrolysis is currently the most advanced technology to produce green hydrogen, but it will not be sufficient on its own: it requires a lot of electricity and its costs are still high. That is why it is essential to explore alternatives such as thermochemical cycles, which allow us to directly harness renewable or residual heat sources to produce hydrogen more efficiently.

2. What exactly is thermochemical water splitting (TWSC), and what sets it apart from other current methods of green hydrogen production?

Thermochemical water splitting is a process in which we use high-temperature chemical reaction cycles to split water into hydrogen and oxygen. Unlike electrolysis, which uses electricity as the input energy, here what we need is heat. This opens the door to integrating sources such as concentrated solar power or residual heat from industrial processes.
In addition, since it is a cyclic process, the same material reacts repeatedly, releasing hydrogen without being consumed in each cycle. The major advantage is that, in theory, we can achieve very high efficiencies with minimal electricity use, as long as the materials are sufficiently stable and cost-effective.

3. What are today’s main technological challenges for thermochemical cycles to move from research to industrial use?

The most important challenge is to find materials that can maintain their performance over thousands of cycles at very high temperatures, without degrading or losing reaction capacity. Many of the compounds studied so far suffer from stability problems or are too expensive to scale. Another challenge is reactor design: we must optimize heat transfer, minimize losses, and ensure process safety.
Finally, there is the cost issue: we need to make hydrogen production through this pathway competitive with electrolysis and, above all, with fossil-based options. This requires progress both in materials science and in systems engineering.

4. What requirements must materials meet to be viable in processes that operate at high temperature and with thousands of operation cycles?

Materials must combine several critical properties: thermal stability, meaning they can withstand temperatures above 1,000 °C without decomposing or degrading; reversibility, so that they can be oxidized and reduced repeatedly without losing efficiency; and mechanical robustness, to withstand the thermal and mechanical stresses inherent to operation.
In addition, they must be abundant, inexpensive, and easy to synthesize, because an excellent material is of little use if it is too scarce or costly to produce at scale. That is why our research focuses on advanced metal oxides and ceramics, which offer a good balance between performance, cost, and durability.

5. How could industries that already generate large amounts of residual heat benefit if they incorporate thermochemical splitting technologies to produce hydrogen?

Many energy-intensive industries, such as steel, cement, or chemicals, produce enormous amounts of residual heat that in most cases is lost. If we manage to harness that heat to power thermochemical cycles, we could transform it into renewable hydrogen.
This would not only reduce emissions, but also allow those industries to valorize a resource they currently do not use and, in addition, produce a clean fuel that can be employed within their own processes or sold as an energy product. It is a way to make industry more efficient and circular, creating new business opportunities while advancing decarbonization.

6. What makes CIC energiGUNE particularly well positioned to drive thermochemical water splitting technologies?

At CIC energiGUNE we have a unique combination of capabilities. On the one hand, we have a specialized team in the design and synthesis of advanced ceramic and metallic materials, capable of withstanding the extreme conditions of these processes. On the other, we have characterization and modeling facilities that allow us to analyze in detail how these materials behave, anticipate their durability, and optimize their performance.
In addition, we actively participate in international projects that connect us with industry and with other leading research centers, which accelerates the transfer of results into real applications. Our goal is clear: to transform thermochemical water cycles from a scientific promise into a viable technology for large-scale green hydrogen production.