In the high resolution XPS spectra

In the high resolution XPS spectra of Cu 2 O/WO 3 -001 catalyst after the fourth cycle (Fig.S7 and Table S3), the peak positions of Cu 2p and W 4f remained nearly unchanged as compared with those of the fresh catalyst. Unfortunately, an obvious raising of W 5+ /W 6+ ratio was observed after four cycles. For exploring the role of W 5+ for photocatalysis, a large amount of W 5+ was obtained for the controlled sample Cu 2 O/r-WO 3 -001 by an electro-reduction method.