The “photolysis” effect was first reported in Science magazine twelve years ago by a team from the Weismann Institute in Israel, who managed to split water (H2O) into H2 and O2, using light and a synthetic catalyst without using electricity. But no one could quite explain how it happened on a molecular level. Now, a doctorate student from the Leibniz Institute for Catalysis (Likat) in Rostock has figured this out and is working on a catalyst that could make it possible to generate green H2 at a very low cost.
Jacob Schneidewind repeatedly recreated the Weismann experiment using a ruthenium catalyst for his doctorate thesis. His goal was to figure out the molecular processes and to simulate them on a computer. What he discovered was unexpected: that the water-splitting reaction was, , “completely different from natural photosynthesis”.
While in green plants, the photosynthetic reaction occurs when every two H2O molecules are split into O2, plus four H2 protons and four electrons which then absorb four light particles at several absorption points, in photolysis, this reaction occurs at only a single point and only requires two photons. Schneidewind ran the experiment using a variety of light sources, from high-energy blue light to the low-energy red range, while colleagues at the University of Rostock analysed the results using high-speed spectroscopy.
Schneidewind explains in a : "Once the first photon has cleared its hurdle, a new compound is formed that absorbs the second photon. And this requires even less energy for the second hurdle than was needed for the first hurdle." Thus, a wider bandwidth of light can be used, which significantly improves efficiency.
The next step is to develop a suitable catalyst for use in a low-cost photolysis system together with a junior team at the RWTH Aachen University. "For example, one could fill transparent plastic tubes with a suspension or solution of water and catalyst and expose them to the sun over a large area," he says. The system could end up being up to four times cheaper than using an electrolyser with solar power to generate H2.