Electrocatalysis: water splitter with multi-tasking talent Precious metal-free composite catalyst plays a double role
Fuel cells are ideal for storing wind and solar energy. They are therefore an important component of the energy transition. The hydrogen required for this is obtained by the electrocatalytic splitting of water, which also releases oxygen. A major step towards optimizing this key electrochemical reaction has now been achieved by researchers from the University of Ulm. The chemists from the Institute of Inorganic Chemistry have developed a precious metal-free composite catalyst that can be used in the same chemical reaction for the development of both oxygen and hydrogen. The results of the project were published in the renowned journal “Angewandte Chemie”.
“The electrochemical reaction in water splitting occurs in two half-reactions: on the one hand, hydrogen is emitted and, on the other hand, oxygen,” explains Professor Carsten Streb from the Institute of Inorganic Chemistry I at the University of Ulm. In conventional electrochemical catalyst systems, different materials are used in these two half reactions. Ulm-based chemists from Professor Streb’s laboratory have now developed a precious metal-free composite material in cooperation with materials scientists from China, which has proven equally effective in both partial reactions. The benefit: “The bi-functional catalyst material simplifies the design and manufacture of systems for electrochemical water splitting.
With a hydrothermal reaction, the metal oxide is deposited on the electrode
In order to be able to realize electrochemical water splitting systems on an industrial scale, catalysts are needed that do not require noble metals such as platinum or iridium. Nevertheless, they must have a high reactivity and be very stable and durable. The Ulm-based chemists have now developed a modular design for such a precious metal-free bi-functional composite material that meets these requirements. “We use both highly reactive cobalt oxide and semiconducting copper oxide to enhance electron transport, and thirdly, tungsten oxide, which is said to structurally and chemically stabilize the catalyst material to make it more durable,” explains Gao , By means of a hydrothermal reaction, this metal-oxide mixture is deposited on an electrode made of conventional macroporous copper foam. The copper foam is electrically very conductive and has a large reaction surface. At the same time, its microstructures are readily accessible to the electrolyte and thus facilitate the release of the gases at the electrode surface.
“The biggest challenge was anchoring the metal oxides with their different functionalities on the surface of the copper foam electrode in such a way that the synthesized material remains chemically as well as mechanically and electrically stable,” says project leader Streb. The scientists are very satisfied with the result.
The nanowires made of copper oxide are very conductive
For example, volumetric measurements were used to investigate the catalytic performance: electron microscopy and X-ray spectroscopic analyzes not only visualized nano- and micrometer-scale material structures, but also demonstrated the chemical nature, crystalline structure and spatial distribution of the different metal-oxide nanostructures become. In the scanning electron micrographs, for example, the needle structure of the highly conductive nanowires made of copper oxide can be excellently detected. Also involved in the project were electron microscopy experts led by Ulm professor Ute Kaiser. The project was funded by the German Research Foundation (DFG) from the Collaborative Research Center TRR 234″CataLight” . Other supporters are the Alexander von Humboldt Foundation, the Helmholtz Association and the Chinese Scholarship Council.
Text, photos : Andrea Weber-Tuckermann