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A path to simple, effective water splitting begins with a decorated nanorod.
During photosynthesis, plants split water into hydrogen ions and oxygen. If researchers could devise a method to mimic nature, the hydrogen could provide a carbon-neutral energy source. A significant challenge to implementing such a technology is developing a system that separates the electrons and the positively charged holes; otherwise, the hydrogen and oxygen could react back into water. Researchers led by Jacek Stolarczyk of Ludwig-Maximilians University Munich and Frank Würthner of the University of Würzburg may have overcome the difficulty by introducing two intermediaries—an oxidation catalyst and platinum particles—to a novel semiconducting nanorod.
The researchers started with an approach that already generated hydrogen but at the nanorod’s expense. When a cadmium sulfide nanorod in water absorbs light, the energy spurs the donation of electrons to a platinum reducing agent. The free H+ can then form H2. But without an oxidation catalyst, the arrangement is unsustainable because the remaining holes oxidize the nanorod’s sulfur lattice. The figure illustrates the researchers’ solution: decorating a newly synthesized CdS nanorod with both platinum nanoparticles and an oxidation catalyst.
The process begins when the nanorod absorbs light, which mobilizes electrons. The oxidation catalyst then draws holes from the length of the nanorod. Each Pt tip attached to either end of the nanorod acts as the electron sink. The oxidation half reaction (red arrows) removes electrons from OH− to produce O2 and water; the reduction half reaction (blue arrows) uses the electrons to covalently bond hydrogen atoms to generate H2. The researchers deployed a fresh chemical group to attach the catalyst to the nanorod. With that innovation, the anchoring group was more resistant to oxidation and the holes were swiftly transferred to the catalyst. (C. M. Wolff et al., Nat. Energy, 2018, doi:10.1038/s41560-018-0229-6.)