Researchers at KAUST have discovered that a form of iron oxide—Fe2O3—makes an excellent co-catalyst for a promising photocatalytic material called gallium nitride for the production f hydrogen. An open-access paper on their work appears in Scientific Reports.
Finding photocatalysts that can efficiently use sunlight to produce clean hydrogen fuel from water is one of the most sought-after applications of solar energy.
Nitrides can absorb most of the energy in the solar spectrum, but gallium nitride is a flawed water splitting photocatalyst. When GaN is used as a photocatalyst, the material is quickly damaged by photocorrosion, which impedes its implementation in industrial applications.—Martin Velazquez-Rizo, a Ph.D. student in the labs of Kazuhiro Ohkawa, who led the current research
Photocorrosion damage was visible after just two hours of photoelectrochemical hydrogen production, the team showed.
To test the possibility of extending the gallium nitride photocatalyst’s working lifetime, the researchers tried combining it with an iron oxide.
Fe2O3 is a well-known material in the catalysis area because of its optical and electronic properties and for its capacity to operate in harsh environments. We anticipated that, under the right conditions, Fe2O3 could suppress the photocorrosion of GaN photocatalysts without diminishing their photoabsorption capabilities.—Martin Velazquez-Rizo
The strategy has proven to be effective. When the team decorated the GaN surface with a 1.3% covering of Fe2O3 particles, the first signs of photocorrosion were more than 20 times slower to appear. In addition, the hydrogen production rate of the Fe2O3/GaN photocatalyst was five times higher than GaN alone. The results, says Velazquez-Rizo, take GaN photocatalysts one step closer to being implemented in real-life applications.
Schematic of the cross-sectional view of the Fe2O3/GaN electrode. Velazquez-Rizo et al.
One reason Fe2O3 and GaN perform well together is likely because of the unusual way in which the Fe2O3 particles are arranged on the GaN surface. The atoms in the iron oxide particles align neatly with the atoms in the GaN lattice below, an effect known as epitaxial growth. This effect is rarely observed when combining materials with different crystallographic properties, such as Fe2O3 and GaN.
The team is continuing to develop new GaN-based composite materials to improve the energy converstion efficiency of photocatalysts.
Velazquez-Rizo, M., Iida, D. & Ohkawa, K. (2020) “Photoelectrochemical and crystalline properties of a GaN photoelectrode loaded with α-Fe2O3 as cocatalyst.” Sci Rep 10, 12586 doi: 10.1038/s41598-020-69419-8