
105Solar Energy Storage with Nanomaterials
prepared using a polymerized approach showed higher photoactivity than the tradi-
tional solid-state method (Li, Chen, et al. 2008).
A niobate photocatalyst (Domen, Kudo, Shibata, et al. 1986; Domen, Kudo,
Shinozaki, et al. 1986), K
4
Nb
6
O
17
(band gap: 3.4 eV; crystal structure: layered struc-
ture) was recently reported as a high and stable material for H
2
evolution from an
aqueous methanol solution without any co-catalysts. Potassium ions are located in
two different kinds of interlayers of this niobate, which are composed of layers of
niobium oxide sheets. The potassium ions between the niobium oxide lay ...