Substrate and secondary battery

According to one embodiment, a substrate includes a semiconductor layer (1). The semiconductor layer (1) comprises tungsten oxide particles (4) having a first peak in a range of 268 to 274 cm, a second peak in a range of 630 to 720 cm, and a third peak in a range of 800 to 810 cmin Raman spectroscopic analysis. The semiconductor layer (1) has a thickness of 1 µm or more. The semiconductor layer (1) has a porosity of 20 to 80 vol%.