Fig. 3. Photocatalytic evaluation of black indium oxide.

a Photocatalytic CO₂ hydrogenation in a batch reactor. Conditions: H₂/CO₂ ratio = 1:1, light intensity = ~20 suns, no external heating and measurement time = 30 min. b Catalytic performance for S4 in a flow reactor at different temperatures, both with and without light irradiation; inset is the enlarged view of the catalytic performance for 200, 225 and 250 °C. c Stability test for S4 in a flow reactor at 300 °C with light irradiation for 70 h. Conditions for flow measurement: atmospheric pressure, H₂/CO₂ ratio = 1:1 with a flow rate of 1 mL min⁻¹ and light intensity of ~8 suns.