This disclosure provides systems, methods, and apparatus related to photoelectrodes. In one aspect, a photoelectrode may include a substrate including an electrically conductive surface and at least one nanostructure in electrical contact with the surface of the substrate. The nanostructure may include an impurity. The impurity may impart a light-absorbing characteristic to the nanostructure.
STATEMENT OF GOVERNMENT SUPPORT
 This invention was made with government support under Contract No. DE-AC02-05CH11231 awarded by the U.S. Department of Energy. The government has certain rights in this invention.