Fig. 3. Schematic and photocatalytic hydrogen evolution performance in the biphase and triphase reaction systems.

a Schematic of the biphase system with water steam/solid photocatalysts/hydrogen gas. b Schematic of a typical triphase system consisting of liquid water/solid photocatalysts/hydrogen gas. c Photo of the biphase photocatalytic system. d Photocatalytic hydrogen gas production rate from the triphase and biphase reaction systems. e Time-dependent photocatalytic hydrogen gas production from water steam with a flow rate of 62 ml h⁻¹. The light source is a solar simulator at AM 1.5 G illumination (100 mW cm⁻²). f The absorption spectra of CoO NPs before and after hydrogen gas production.