Photocatalytic water splitting and alcohol reforming offer promising alternatives for clean H₂ production, in contrast to the industrially applied steam reforming of fossil fuels. However, the understanding of the reaction mechanisms, which is indispensable for tailored performance improvement, is complicated by the structural complexity of powdered catalyst. In contrast, well-defined planar catalysts are already used for fundamental studies in ultra-high vacuum, but a simple extrapolation of the results to applied conditions is impractical due to a significant pressure difference.

Therefore, we developed a µ-photoreactor for the evaluation of planar model catalysts like single crystals or epitaxially grown semiconductors at ambient conditions in a continuous gas flow. In this system, the catalyst serves as the bottom of the reactor, while a 200 µm sealing on top defines the reactor volume of only 10.5 µL. The reactor is closed by a UV-vis transparent lid, which allows illumination with an interchangeable light source. It contains lithographically implemented channels for gas feed access. The entire gas flowing through the reactor is transmitted to a QMS by a capillary, which enables time-resolved reaction monitoring with high sensitivity at ambient pressure.

We already demonstrated the functionality of the device by the photooxidation of ethanol over Pt loaded TiO₂ (P25) at varying illumination intensities. This device provides new testing possibilities for low photocatalyst amounts (µg scale) and planar catalysts like films including the option of post-reaction characterization.