A high-performance solar photocatalyst based on titanium dioxide (TiO2) and other “metallic” oxides has been shown to greatly enhance visible light absorption, enabling more efficient use of the solar spectrum for energy applications. Combining aspects of condensed matter physics, semiconductor device engineering and photochemistry, researchers at the University of Illinois coupled the correlated electron “metal” strontium ruthenium oxide (SrRuO3) with TiO2 to create heterostructures that could advance the field of photocatalysis and broaden the potential applications of other metallic oxides. “When designing next-generation solar energy conversion systems, we must first develop ways to more efficiently utilize the solar spectrum,” said research leader Lane Martin, assistant professor of materials science and engineering at the university. Martin said the primary feature limiting the performance of oxide-based photovoltaic and/or photocatalytic systems has traditionally been the poor absorption of visible light in these often wide bandgap materials. Anatase TiO2 — the backbone of dye-sensitized solar cells — is the most widely-studied photocatalyst based on its chemical stability, nontoxicity and good band alignment to several oxidation-reduction reactions, but the presence of a light-absorbing dye accounts for a large bandgap, limiting efficient use of all but the UV portion of sunlight. SrRu03 possesses metalliclike temperature dependence of its resistivity and itinerant ferromagnetism. Referring to this material as a metal, however, is likely inappropriate because the electronic structure and properties are derived from a combination of complex electronic density of states, electron correlations, and more. “We observed that the unusual electronic structure of SrRuO3 is also responsible for unexpected optical properties, including high absorption across the visible spectrum and low reflection compared to traditional metals,” said Sungki Lee, first author of the paper, which appeared in Advanced Energy Materials (doi: 10.1002/aenm.201201116). The correlated electron “metal” SrRuO3 exhibits strong visible light absorption, according to a new study out of the University of Illinois’s College of Engineering. Overlaid here on the AM1.5G solar spectrum, SrRuO3 is shown to absorb 75 times more light than TiO2. The structural, chemical and electronic compatibility of TiO2 and SrRuO3 further enables the fabrication of heterojunctions with exciting photovoltaic and photocatalytic response driven by hot-carrier injection. Courtesy of Lane Martin, University of Illinois. "This is a fundamentally new way of approaching these matters,” Martin said. “From these materials, we can imagine carbon-neutral energy production of clean-burning fuels, wastewater purification and remediation, and much more.” The work has resulted in a provisional patent application. It was supported by the ongoing International Institute for Carbon Neutral Energy Research program, a partnership between the University of Illinois and Kyushu University in Japan. For more information, visit: www.illinois.edu