Getting more out of energy materials: Researchers at e-conversion have recently taken a significant step toward this goal. The research team, led by Prof. Bettina Lotsch, Professor at the Max Planck Institute of Solid State Research in Stuttgart, skillfully integrated single metal atoms into covalent organic frameworks, or COFs for short. This synthetic trick enabled the material to absorb a more significant portion of sunlight.

Andrés Rodríguez-Camargo created a compound that can absorb significantly more solar energy by embedding palladium atoms in covalent organic framework compounds. (Photo: Tigmansu Pal/MPG)

Improving photocatalytic performance: The researchers have already successfully used their new compound to produce hydrogen peroxide (H₂O₂) under light with a wavelength of 810 nm. (Artwork: ScienceBrush Design)

COFs are among the most promising energy materials because their properties can be finely tuned through their molecular structure. Their application as light-harvesting materials for photocatalytic solar energy conversion was first demonstrated in 2014 by the same group. Since then, COFs have rapidly evolved as photocatalysts, for instance, for H₂ production. However, these applications have so far been limited to visible light (< 760 nm). “By incorporating single palladium atoms into the molecular framework of a specific COF, known as the TpAzo-COF, we were able to extend light absorption into the near-infrared region,” explains Andrés Rodríguez-Camargo, a doctoral student and first author of the recently published scientific article. “This region comprises about 50 percent of the solar spectrum and has remained untapped until now. We can absorb significantly more solar energy with our new material,” says Rodríguez-Camargo.

Palladium enhances the molecular framework

To produce the modified COF, the researchers employed a novel method of cyclopalladation. This approach enables the precise atomic integration of palladium atoms into the material. The resulting compound contains 12 weight percent of the metal. Notably, the palladium atoms are homogeneously distributed within the COF, preventing the formation of unwanted nanoparticles. The integration of palladium shifts the light absorption toward higher wavelengths. This change is even visible to the naked eye: while the initial substance is red, it turns into a very dark shade of red after palladium is incorporated. “Everyone knows from summer experience that wearing a dark-colored T-shirt makes you feel much warmer than lighter-colored clothing—this is a tangible indication of infrared absorption,” Rodríguez-Camargo explains. Spectroscopic analyses confirm these changes and detail the optical modifications.

The integration of palladium causes the light absorption to shift to higher wavelengths. While the initial substance is red, it becomes darker and darker as the palladium load increases. (Photo: Andrés Rodríguez-Camargo)

H₂O₂ as solar fuel: A potentially sustainable energy source

Beyond the expanded light absorption, the palladium-based active centers impart semiconductor-like properties to the material, significantly improving its photocatalytic performance. The researchers have already successfully used their new compound to produce hydrogen peroxide (H₂O₂) under light with a wavelength of 810 nm. H₂O₂ is an important industrial chemical and a potential solar fuel candidate. As a liquid energy carrier, it can store solar energy and release it through controlled decomposition into water and oxygen. The capabilities of palladium-functionalized COFs demonstrate that these materials not only have the potential to revolutionize chemical synthesis but also contribute to the development of sustainable energy systems. “With our approach, we have developed the world’s first COF photocatalyst material active in the near-infrared region,” explains Prof. Bettina Lotsch. “This opens entirely new pathways for full-spectrum photocatalysis and contributes to a much more efficient use of solar energy,” she adds.

Publication:

A. Rodríguez-Camargo, M.W. Terban, M. Paetsch, E.A. Rico, D. Graf, R. Hirpara, V. Duppel, I. Moudrakovski, M. Etter, N. Guijarro, C. Ochsenfeld, R.E. Dinnebier, L. Yao, B.V. Lotsch; Cyclopalladation of a covalent organic framework for near-infrared-light-driven photocatalytic hydrogen peroxide production. Nat. Synth (2025). https://doi.org/10.1038/s44160-024-00731-1

Contact:

Prof. Bettina Lotsch
Nanochemistry Department
Max Planck Institute for Solid State Research
b.lotsch@fkf.mpg.de