Patent ID: 8734625

Claim:
A hydrogen generation device comprising: a transparent substrate; a photocatalytic electrode formed of a transparent conductive layer disposed on the transparent substrate and a photocatalytic layer disposed on the transparent conductive layer; a counter electrode connected electrically to the transparent conductive layer; a water-containing electrolyte solution layer provided between the photocatalytic electrode and the counter electrode; a separator that separates the electrolyte solution layer into a first electrolyte solution layer in contact with the photocatalytic electrode and a second electrolyte solution layer in contact with the counter electrode; a first gas outlet, connected to the first electrolyte solution layer, for discharging oxygen gas or hydrogen gas generated in the first electrolyte solution layer; and a second gas outlet, connected to the second electrolyte solution layer, for discharging hydrogen gas or oxygen gas generated in the second electrolyte solution layer, wherein the photocatalytic electrode and the counter electrode are arranged so that a surface of the photocatalytic layer and a surface of the counter electrode face each other, the separator allows an electrolyte in the electrolyte solution layer to pass therethrough and prevents hydrogen gas and oxygen gas in the electrolyte solution layer from passing therethrough, a light irradiation efficiency when the photocatalytic layer is irradiated with light from a side of the transparent substrate is lower than a light irradiation efficiency when the photocatalytic layer is irradiated with light from a side of the photocatalytic layer, the photocatalytic layer is formed of a first n-type semiconductor layer and a second n-type semiconductor layer disposed in this order from a side of the transparent conductive layer, or a first p-type semiconductor layer and a second p-type semiconductor layer disposed in this order from a side of the transparent conductive layer, when the photocatalytic layer is formed of the first n-type semiconductor layer and the second n-type semiconductor layer, relative to a vacuum level, (I) band edge levels of a conduction band and a valence band in the second n-type semiconductor layer, respectively, are higher than band edge levels of a conduction band and a valence band in the first n-type semiconductor layer, and (II) a Fermi level of the first n-type semiconductor layer is higher than a Fermi level of the second n-type semiconductor layer, and when the photocatalytic layer is formed of the first p-type semiconductor layer and the second p-type semiconductor layer, relative to a vacuum level, (I) band edge levels of a conduction band and a valence band in the second p-type semiconductor layer, respectively, are lower than band edge levels of a conduction band and a valence band in the first p-type semiconductor layer, and (II) a Fermi level of the first p-type semiconductor layer is lower than a Fermi level of the second p-type semiconductor layer.