Chen et al.[11] reported that monoc

Chen et al.[11] reported that monoclinic WO 3 nanosheet exhibited better photocatalytic activity for CO 2 reduction than that of commercial WO 3 powder. Monoclinic and hexagonal WO 3 are the most attractive candidates among the various crystal phases. The monoclinic phase is the most stable phase, while the hexagonal phase possesses open-tunnel structure and rich intercalation chemistry. Meanwhile, different crystalline structures of WO 3 could result in dissimilar electronic properties, and thus cause differences in photocatalytic activity for CO 2 reduction