This work investigates long-term photoelectrochemical hydrogen evolution (82 days) in 1 M HClO4 using a TiO2:H protected crystalline Si-based photocathode with metal-oxide-semiconductor (MOS) junctions. It is shown that day/night cycling leads to relatively rapid performance degradation while the photocurrent under the continuous light condition is relatively stable. We observed that the performance loss is mainly due to contamination of the catalytically active surface with carbonaceous material. By ultraviolet (UV) light exposure, we also observed that the activity can be restored, most likely due to photocatalytic degradation of organic compounds by the UV light excited TiO2 protection layer.@en