Abstract
Single crystal samples of reduced rutile used as anodes in a photoelectrochemical cell with 
show significant changes with use. Saturated photocurrent as a function of illumination wavelength and differential capacitance as a function of anode half‐cell voltage were measured before and after varying periods of operation under intense illumination. Shifts in the photoresponse and capacitance are observed only when the illuminating photon energy exceeds the bandgap energy of rutile and when a field exists in the crystal. The changes, possibly indicating a motion of donors toward the crystal surface, are also accompanied by an eventual loss in quantum efficiency and striking alterations in surface morphology. Reduced rutile may not have sufficient stability for prolonged use as the anode in electrochemical cells.