Water-splitting step proceeds 100% efficiently

Researchers have set a record for part of the process of using sunlight to split water, reporting 100% efficiency for the half-reaction that evolves hydrogen, a clean-burning fuel (Nano Lett. 2016, DOI: 10.1021/acs.nanolett.5b04813). One factor limiting the efficiency of water splitting is the tendency of excited electrons and positive charges generated during light absorption to rapidly recombine. The electrons are needed to reduce protons to molecular hydrogen. So Lilac Amirav of Technion—Israel Institute of Technology and her colleagues designed a nanoparticle-based photocatalyst that keeps the charges separated. They created a light-harvesting cadmium sulfide quantum rod with a quantum dot of cadmium selenide embedded near one end and a platinum tip on the other. When suspended in water and exposed to visible light, the CdS quantum rod absorbs photons, releasing electrons. The rod transfers electrons to the platinum tip, reducing protons to hydrogen and leaving behind positively charged holes in the CdSe dot. The researchers achieved their record conversion by adjusting the pH and adding isopropyl alcohol to the water. These conditions prevent charge recombination, leaving more electrons available to produce hydrogen.