Porous metal-organic framework catalysts

The development of technologies for sustainable energy carriers, such as hydrogen, is essential. A promising way to produce hydrogen (H₂) is from splitting water into H₂ and oxygen (O₂), either electrochemically or using light, or both – a path that the team follows. However, this process requires a catalyst that accelerates the reaction without being consumed. Key criteria for a catalyst include a large surface area for the adsorption and splitting of water molecules, and durability for long-term use.

Zeolitic imidazolate frameworks (ZIFs), a class of hybrid organic/inorganic materials with molecular interfaces and numerous pores, offer record surface areas and ample adsorption sites for water as catalysts. They consist of single metal ions, such as cobalt ions, which are connected by specific organic molecules, called ligands, through what is called coordination bonds. Conventional ZIFs only contain a single type of organic ligand. "These ZIFs often lack stability in water under electrocatalytic conditions to ensure long-term application. Furthermore, their rather low electronic conductivity also limits their effectiveness in electrocatalytic applications, " says Dominik Eder.

To address these challenges, the team has developed a way to design ZIFs using two or more organic ligands. ”We needed to be careful to mix both ligands in a way that creates a uniform distribution throughout the framework, while preserving the original ZIF structure" explains Zheao Huang, the study’s lead author. Therefore, the team comprehensively investigated a series of ligand combinations and process parameters and was finally able to identify the best suited ligand pair.

Synergistic benefits by mixing two organic ligands

The authors found that this modification has significantly improved the ZIF stability, extending its durability during electrocatalytic water splitting from a few minutes to at least one day. Through in-depth investigations using a wide range of experimental spectroscopic and microscopic techniques, supported by computational theory in collaboration with Central China Normal University, the team observed that the precise mixing of the two ligands synergistically strengthened the coordination bond with the cobalt metal. As a result, the porous framework did not collapse during the (photo)electrocatalytic tests. "Instead, we observed that after just a few minutes of the reaction a very thin film of just a few nanometers, made of cobalt oxyhydroxide, was formed on the surface of the ZIF nanoparticles, which prevented further degradation and collapse," says Huang Zheao.

Additionally, the combination of two ligands has increased the conductivity of the ZIF material by ten times, consequently boosting also the oxygen evolution reaction (OER) rate by ten times. "Simulations revealed that the two ligands interact in a synergistic way, creating a high density of mobile charge carriers throughout the material," explains Dominik Eder and adds, ”Although we expected some improvements with this new strategy, we were surprised by how much it enhanced the (photo)electrocatalytic performance of ZIFs.”

Future Prospects and Broader Applications

The team is now exploring this versatile approach for other ZIFs as well as metal-organic frameworks (MOFs) that also lack stability and conductivity in electrocatalytic and (photo)electrocatalytic applications. This innovative approach opens exciting possibilities for designing advanced materials for catalysis, sensing and solar energy conversion technologies, moving us closer to real-world applications.

Original publication

Ligand Engineering Enhances (Photo)Electrocatalytic Activity and Stability of Zeolitic Imidazolate Frameworks via In-situ Surface Reconstruction. Nature Communications. https://doi.org/10.1038/s41467-024-53385-0, opens an external URL in a new window

Contact

Prof. Dominik Eder
TU Wien
Institute of Materials Chemistry
+43 1 58801 165400
dominik.eder@tuwien.ac.at

Projektass. Zheao Huang
TU Wien
Institute of Materials Chemistry
zheao.huang@tuwien.ac.at

Sender
Sarah Link, M. A.
PR and Marketing
Technische Universität Wien
+43 664 605882412
sarah.link@tuwien.ac.at