THE ROLE OF METAL-HYDRIDES IN ELECTRODE-REACTIONS ON METAL-OXIDE SEMICONDUCTORS

Metal hydrides formed on metal oxide semiconductors during reduction i n a hydrogen flow have been found to play an important role in electro de reactions, especially in the oxidation of water. By using a rotatin g-ring disk electrode, the difference in electrode kinetics between Ti O2 reduced in a N-2 and a H-2 flow was clarified. The TiO2 used was ma de by the sol-gel method, which allowed a large tunnel current. This a lso allows us to compare the difference between oxidation by a hole tr ansfer under light illumination, photooxidation, and by an electron tr ansfer under a tunneling in the dark, tunnel oxidation. It has been fo und that the collection efficiencies, N-8, in tunnel oxidation are ind ependent of the rotational speed and much larger than those in photoox idation. Some catalytic enhancement of the ring current due to oxidati on products produced at the TiO2 disk and carried away to the Pt ring is discussed.