Co-Fe layered double hydroxide for oxygen evolving photocatalyst under visible light

Abstract

The artificial photosynthesis means conversion of solar energy to chemical energy such as hydrogen, methanol and so on. Recent increasing interests in alternative energy, have caused by the Global Warming, make artificial photosynthesis more attractive. Water splitting, one part of artificial photosynthesis, is the simplest way to make hydrogen and is promising for energy applications. Instead of overall water splitting owing to its technical limitation, it is separately investigated by water oxidation and water reduction. Water oxidation is more difficult between them because it needs 4 electrons in one reaction. Layered Double Hydroxides(LDHs) are generally known as an effective photocatalysts for water oxidation. This material can transfer electrons through metal-to-metal charge transfer(MMCT) easily and effectively. Cobalt and iron, used in this experimental, have extensively used for photocatalysts. Cobalt oxide has good property for photocatalytic reaction due to its low turnover frequency but it can oxidize water by itself. Otherwise, iron oxide has proper band structure for water oxidation but its hole diffusion length is too short to oxidize water effectively. Therefore, we hybridized these two materials to get effective water oxidation photocatalyst which is reactive under visible light irradiation. Co-Fe LDH is made by co-precipitation method. Cobalt and iron precursor were dissolved in anion packing solution. This solution was purged by argon gas and heated for several hours. And then, brown-colored powder were recovered by centrifuging and dried in vacuum oven overnight. From XRD and HRTEM, this material has layered structure distinguished another materials. Also, Co-Fe LDH in water with sacrificial agent makes some oxygen under visible light irradiation. From UV-vis spectroscopy and UPS, the band structure is suitable for oxygen evolving. If we use this water oxidation system with other water reduction system, we would get full water splitting reaction system in near future.