NOVELTY - A photoelectrolytic apparatus comprises housing (38) capable of holding an aqueous medium, permitting ultraviolet and visible light (37) to enter the interior of housing; an electrode (39) comprising substrate having undulating surface and semiconductor film conforming to undulating surface so as to induce a stress 100 mPa in part of semiconductor film, thus altering bandgap of the stressed part of semiconductor film; a second electrode (44); and means for collecting hydrogen gas generated at second electrode free from oxygen generated at the semiconductor film.    USE - As a photoelectrolytic apparatus for production of hydrogen gas from an aqueous medium (claimed) and in other applications such as photovoltaics (electrical power from sunlight), photocatalytic disinfection and detoxification, point-of-use photoelectrolysis for use in internal combustion engines, for example, and stress-induced tunable bandgap components for communications.    ADVANTAGE - In the photoelectrolytic device, stress is induced and managed in a thin film of titania in order to shift and lower the bandgap energy into the longer wavelengths that are more abundant in sunlight to match the band gap of the titania more efficiently with the solar spectrum at the earth's surface for photoelectrolysis. Thus the semiconductor photocatalyst has a bandgap that is better matched to the solar spectrum and/or artificial illumination for higher efficiency or even to work at all. The photocatalyst increase photocatalytic surface area, and prevents delamination of the film from the substrate.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a process for generating hydrogen from water involving providing an electrode comprising a substrate having an undulating surface and semiconductor film on the undulating surface, where the semiconductor film conforms to the undulating surface so as to induce a stress of 100 mPa in part of the semiconductor film, thus altering the bandgap of the stressed part of the semiconductor film; and contacting the semiconductor film with an aqueous medium while illuminating the semiconductor film, thus causing the semiconductor film to generate hydrogen from the aqueous medium.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of a complete photoelectrolysis cell employing stress-induced band-gap shifted titania as one of the electrodes.    UV or visible light (37)    Housing (38)    Titania coated electrode (39)    Separator membrane (41)    Second electrode (44)