Crystallization of Tungsten Trioxide Having Small Mesopores: Highly Efficient Photoanode for Visible-Light-Driven Water Oxidation

摘要

Recent developments of nanostructured materials have widened their application in photoelectrochemical (PEC) water splitting for direct conversion of solar energy into green and storable hydrogen fuel.Water oxidation is considered to be the energy-demanding bottleneck in PEC solar fuel devices and thus related photoanode materials have been extensively studied. Tungsten trioxide (WO3) has attracted immense attention as a photoanode material in PEC devices because of its visible-light response (band gap, E_g = 2.6-2.8 eV), a favorable valance band edge position for O2 evolution (3 V versus the normal hydrogen electrode, NHE), and good photochemical stability. So far, the mesoporous architectures of photoanodes are promising for applications in solar energy conversion. A system having organized small mesopores (pore diameter, about 2-3 nm) can offer 1) a large internal surface area; and 2) a shorter solid-state carrier diffusion length in the nanosized wall (<10nm; Scheme la); owing to their smaller void spaces inside pores and slimmer pore walls relative to conventional (pore diameter, about 5-10 nm) and interpar-ticle (particles spacing, >15 nm) mesoporous systems. However, particularly in case of WO3 high crystallinity is needed for a PEC performance as a photoanode.