A photoelectrolysis cell is described herein. The cell includes a photoelectrode based on a material having the general formula (Ln1−xMx)(Nb1−yTay)O1+xN2−x. Ln is at least one lanthanide element; M is at least one alkaline earth metal; 0≦x≦0.99; and 0≦y≦1. The photoelectrolysis cell further includes a counter-electrode formed from at least one metal or metallic alloy. An electrolyte which is in contact with both the photoelectrode and the counter-electrode is another component of the cell, along with a means for collecting hydrogen produced by the cell. A related process for producing hydrogen in a photoelectrolysis cell is also described.