Combinatorial discovery through a distributed outreach program: Investigation of the photoelectrolysis activity of p-type Fe, Cr, Al oxides

We report the identification of a semiconducting p-type oxide containing iron, aluminum, and chromium (Fe_2-x-yCr_xAl _yO₃) with previously unreported photoelectrolysis activity that was discovered by an undergraduate scientist participating in the Solar Hydrogen Activity research Kit (SHArK) program. The SHArK program is a distributed combinatorial science outreach program designed to provide a simple and inexpensive way for high school and undergraduate students to participate in the search for metal oxide materials that are active for the photoelectrolysis of water. The identified Fe_2-x-yCr_xAl_yO ₃ photoelectrolysis material possesses many properties that make it a promising candidate for further optimization for potential application in a photoelectrolysis device. In addition to being composed of earth abundant elements, the FeCrAl oxide material has a band gap of 1.8 eV. Current-potential measurements for Fe_2-x-yCr_xAl_yO₃ showed an open circuit photovoltage of nearly 1 V; however, the absorbed photon conversion efficiency for hydrogen evolution was low (2.4 × 10 ^-4 at 530 nm) albeit without any deposited hydrogen evolution catalyst. X-ray diffraction of the pyrolyzed polycrystalline thin Fe _2-x-yCr_xAl_yO₃ film on fluorine-doped tin oxide substrates shows a hexagonal phase (hematite structure) and scanning electron microscope images show morphology consisting of small crystallites.