Quantification of photocatalytic hydrogen evolution

A new photoreactor with defined irradiation geometry was developed and tested for the water reduction reaction using carbon nitride (C3N4) as a photocatalyst. The hydrogen evolution rate was investigated with a sun simulator (I = 1000 W m(-2)) in two different operation modes: circulation and stirring of the catalyst dispersion. Only in the stirred mode, where shear stress is lower, a stable hydrogen evolution rate of about 0.41 L m(-2) h(-1) is obtained. It is confirmed by experiments with D2O that hydrogen is obtained from the water splitting process and not by dehydrogenation of the sacrificial agent. The obtained rate results in an efficiency of <0.1% based on a reference experiment with a photovoltaic-powered electrolysis setup. The change from distilled water to tap or simulated sea water results in a lower hydrogen evolution rate of about 50%.