Engineers turn sunlight into hydrogen

RESEARCHERS from the Ulsan National Institute of Science and Technology (UNIST) near Ulsan, South Korea have developed a photoelectrode that can boost the efficiency of solar water-splitting to make hydrogen.

The multilayered photoelectrode is a two-dimensional hybrid structure consisting of three layers of gold film (100 nm), an ultrathin layer of TiO₂ (20 nm), and gold nanoparticles – (Au NPs/TiO₂/Au). The structure of the photoelectrode allows 90% light absorbtion in the visible spectrum, and can absorb into the UV-visible spectrum (up to 800 nm).

The technique is inspired by plants converting sunlight into energy. The team claims that the photoelectrode can absorb visible solar light to split water molecules into hydrogen and oxygen. Other techniques for hydrogen production with TiO₂ photocatalysts alone break down organic matter to produce CO₂ and water as by-products.

The team reports the design can absorb light into the entire UV-visible region of the solar spectrum due to the addition of the gold film, and absorbance in the visible region increases by 30% when the layer of gold nanoparticles and TiO₂ is added.

Jeong Min Baik, professor of materials science and engineering at UNIST said, “Several attempts have been made to use UV-based photoelectrodes for hydrogen production, but this is the first time to use the hybrid-structured film with TiO₂ for oxygen production.”

The team also suggests the specific assemblies of the nanaoparticles arranged in branching or hierarchy formations are best for absorbing UV-visible light. The team reports that the (Au NPs/TiO₂/Au) photoelectrode is 7.4 times more efficient at water-splitting compared with a (TiO₂/Au) photoelectrode.

Heon Lee, professor of materials science and engineering at Korea University added, “This hybrid-structured film is expected to further reduce the overall cost of producing hydrogen, as it doesn’t require complex operation processes.”

Nano Energy. DOI: 10.1016/j.nanoen.2016.01.004