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Artificial photosynthesis

Learning from nature

München, 03/10/2017

A novel carbon nitride-based polymer is capable of storing electrons energized by sunlight for hours and releasing them on demand. The system might provide the basis for the storage of solar energy in the future.

A research team led by Bettina Lotsch, Professor of Functional Nanostructures in the Department of Chemistry at LMU and leader of a research group at the Max Planck Institute for Solid-State Research in Stuttgart, reports a promising breakthrough in “artificial photosynthesis”. Lotsch and her colleagues have developed a carbon nitride polymer with a graphite-like network structure, which carries out a crucial step in the light-driven generation of molecular hydrogen from water in a manner that mimics the mechanism used by photosynthetic organisms more closely than other synthetic materials. The compound is capable of sequestering electrons provided by an electron donor upon irradiation with sunlight, and subsequently releasing them for use in hydrogen production. The findings appear in the latest issue of the journal Angewandte Chemie.

The novel carbon nitride-based polymer thus makes it possible to separate the so-called light and dark reactions involved in photosynthesis. As in the case of natural photosynthesis, the first step involves the absorption of light energy by the new polymer to extract an electron from the electron donor. Strikingly, this high-energy electron can be stored in the new compound as a long-lived radical which is intensely blue in color. This state is stable for hours, and these highly energetic electrons can subsequently be released upon the addition of a hydrogen evolution co-catalyst. The compound’s ability to store electrons and give them off on demand means that the hydrogen gas can be generated independently of sunlight. In fact, this step can be performed in the dark. “Both processes – the light-driven photoreduction step and the catalytic conversion of water into molecular hydrogen – take place in the same material. That is the great advantage of this system in comparison with the approaches used so far, in which the production and consumption of charge carriers either cannot be separated or – as in the case of biological photosynthesis – the mobile electrons must be passed along a complex chain of electron transporters so that the energy can be captured and stored in the molecules NADPH and ATP,” says Bettina Lotsch. Furthermore, production of the polymer itself is simple and economical, she adds.

The new material thus has the basic properties required to serve as a chemical system for the sequestration of solar energy. “Our system can absorb solar energy for a considerable time and release it on demand,” says Filip Podjaski, a doctoral student in Lotsch’s group. The chemists involved in this collaboration between groups at LMU-MPI, Zürich and Cambridge hope that they can now develop practical forms of solar energy storage that can provide sustainable energy when it is needed – irrespective of whether or not the Sun happens to be out. (Angewandte Chemie 2016)

For more information on Bettina Lotsch’s work, see: