Microwaves Could Make for Greener Hydrogen
Hydrogen has shown great promise as a next-generation fuel due to its abundance and zero carbon emissions. Among the various pathways to produce clean hydrogen, thermochemical methods have attracted much attention due to their scalability. However, existing thermochemical hydrogen production technologies rely on the oxidation-reduction of metal oxides, which requires extremely high temperatures—up to 1,500 °C—and a large temperature swing, posing significant challenges for practical implementation.
To address these challenges, an interdisciplinary research team at Pohang University of Science & Technology (POSTECH)—mechanical engineering professor Hyungyu Jin, physics professor Gunsu S. Yun, and doctoral students Dongkyu Lee and Jaemin Yoo—set out to discover a way to enhance the efficiency and reduce the temperature of this process. They believe they have discovered a pathway involving heating through microwaves.
As they discussed their research interests, they realized that integrating microwave plasma as an additional driving force might effectively lower the reaction temperature needed for thermochemical water splitting.
Initially, the challenge was to merge microwave plasma into the conventional, heat-driven thermochemical water splitting process that uses metal oxides as catalysts. This approach produced a very encouraging result, but encountered significant difficulties in reproducibility and controllability due to the instability of plasma under the demanding reaction conditions.
The team then wanted to see if microwaves alone—without forming plasma—could interact directly with metal oxides, similar to the principle of microwave induction heating, provided the metal oxides can absorb enough energy.
“This insight prompted us to shift our focus and test the new approach,” Jin said.
The results were impressive.
The direct interaction between microwaves and metal oxides (Gd-doped ceria [CeO2]) reduced the reaction temperature to below 600 °C, cutting the temperature requirement by over 60 percent. Remarkably, microwave energy was found to replace 75 percent of the thermal energy needed to break down water into hydrogen and oxygen, a breakthrough for sustainable hydrogen production.
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Also at this lower temperature, the metal oxide generated abundant oxygen vacancy defects—an outcome typically achievable only above 1,300 °C through conventional heat-based methods. These oxygen vacancies or “gaps” serve as active sites for water splitting, and their formation is crucial in boosting hydrogen production.
Another unexpected finding was the dramatic enhancement in reaction kinetics.
“While chemical reaction rates generally increase with temperature, our microwave-assisted process achieved rapid reaction cycles at much lower temperatures,” Jin said. “For example, a thermochemical water splitting cycle that conventionally requires about one hour at temperatures exceeding 1,300 °C was completed in just a few minutes using microwaves.
Although the concept of beneficial material defects may be unfamiliar to mechanical engineers, the overall reaction chemistry is firmly rooted in chemical thermodynamics. “Mechanical engineers will recognize how microwaves can favorably alter reaction thermodynamics in a way that lowers the required reaction temperature and creates abundant oxygen vacancy defects,” Jin said.
“The innovative aspects of our approach—ranging from our novel use of microwave interactions with metal oxides to our integrated thermodynamic analysis—set this research apart as a significant contribution to the field,” Yun added.
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Looking ahead at future research, the team will pursue three key directions, The first is catalyst development—identifying and optimizing metal oxide catalysts that fully harness microwave energy for even greater efficiency. Then the team will need to scale up the system, developing scalable reaction systems that seamlessly integrate heat, microwave energy, and catalysts to move the technology closer to commercial application.
Finally, the team must expand the number of applications. This will involve exploring the application of microwave-assisted techniques to a wider range of chemical reactions, such as syngas production and carbon-neutral fuel synthesis.
“We believe that the principles underlying microwave-assisted thermochemical reactions hold promise for a broad spectrum of applications,” Yun said. “In theory, any redox reaction involving metal oxide catalysts could benefit from the enhanced efficiency and reduced temperatures offered by our new approach. This mechanism could fundamentally transform existing chemical processes and pave the way for innovative products across various industries.”
Mark Crawford is a technology writer in Corrales, N.M.
To address these challenges, an interdisciplinary research team at Pohang University of Science & Technology (POSTECH)—mechanical engineering professor Hyungyu Jin, physics professor Gunsu S. Yun, and doctoral students Dongkyu Lee and Jaemin Yoo—set out to discover a way to enhance the efficiency and reduce the temperature of this process. They believe they have discovered a pathway involving heating through microwaves.
A lunch meeting of minds
They developed their new idea over a casual lunch meeting. Jin had been seeking a way to lower the reaction temperature required for hydrogen production through thermochemical water splitting—a process traditionally needing temperatures over 1,300 °C, which is incompatible with existing industrial infrastructure. Meanwhile, Yun, an expert in plasma physics, had been testing the capability of microwave-driven plasmas to redox reactions of iron oxides.As they discussed their research interests, they realized that integrating microwave plasma as an additional driving force might effectively lower the reaction temperature needed for thermochemical water splitting.
Initially, the challenge was to merge microwave plasma into the conventional, heat-driven thermochemical water splitting process that uses metal oxides as catalysts. This approach produced a very encouraging result, but encountered significant difficulties in reproducibility and controllability due to the instability of plasma under the demanding reaction conditions.
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The team then wanted to see if microwaves alone—without forming plasma—could interact directly with metal oxides, similar to the principle of microwave induction heating, provided the metal oxides can absorb enough energy.
“This insight prompted us to shift our focus and test the new approach,” Jin said.
The results were impressive.
The direct interaction between microwaves and metal oxides (Gd-doped ceria [CeO2]) reduced the reaction temperature to below 600 °C, cutting the temperature requirement by over 60 percent. Remarkably, microwave energy was found to replace 75 percent of the thermal energy needed to break down water into hydrogen and oxygen, a breakthrough for sustainable hydrogen production.
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Also at this lower temperature, the metal oxide generated abundant oxygen vacancy defects—an outcome typically achievable only above 1,300 °C through conventional heat-based methods. These oxygen vacancies or “gaps” serve as active sites for water splitting, and their formation is crucial in boosting hydrogen production.
Another unexpected finding was the dramatic enhancement in reaction kinetics.
“While chemical reaction rates generally increase with temperature, our microwave-assisted process achieved rapid reaction cycles at much lower temperatures,” Jin said. “For example, a thermochemical water splitting cycle that conventionally requires about one hour at temperatures exceeding 1,300 °C was completed in just a few minutes using microwaves.
Although the concept of beneficial material defects may be unfamiliar to mechanical engineers, the overall reaction chemistry is firmly rooted in chemical thermodynamics. “Mechanical engineers will recognize how microwaves can favorably alter reaction thermodynamics in a way that lowers the required reaction temperature and creates abundant oxygen vacancy defects,” Jin said.
More developments to come
This research represents the first systematic thermodynamic study of microwave-assisted thermochemical water splitting. Both the theoretical analyses and experimental methodologies break new ground in this emerging area.“The innovative aspects of our approach—ranging from our novel use of microwave interactions with metal oxides to our integrated thermodynamic analysis—set this research apart as a significant contribution to the field,” Yun added.
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Looking ahead at future research, the team will pursue three key directions, The first is catalyst development—identifying and optimizing metal oxide catalysts that fully harness microwave energy for even greater efficiency. Then the team will need to scale up the system, developing scalable reaction systems that seamlessly integrate heat, microwave energy, and catalysts to move the technology closer to commercial application.
Finally, the team must expand the number of applications. This will involve exploring the application of microwave-assisted techniques to a wider range of chemical reactions, such as syngas production and carbon-neutral fuel synthesis.
“We believe that the principles underlying microwave-assisted thermochemical reactions hold promise for a broad spectrum of applications,” Yun said. “In theory, any redox reaction involving metal oxide catalysts could benefit from the enhanced efficiency and reduced temperatures offered by our new approach. This mechanism could fundamentally transform existing chemical processes and pave the way for innovative products across various industries.”
Mark Crawford is a technology writer in Corrales, N.M.
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