RATE-DETERMINING STEP IN PHOTOCATALYTIC PRODUCTION OF HYDROGEN

Photocurrent and dark current measurements were made using n-type and p-type Si electrodes with thin Pd overlayers to determine the rate-determining step in the photocatalytic production of hydrogen. Since exposure of Pd to hydrogen is known to reduce its work function, the possible change in Schottky barrier height was investigated by measuring the onset potential for photocurrent of Si/SiOx/Pd electrodes before and after exposing the electrode surface to hydrogen. At low light intensity (6.4 μW cm-2), the results for n-type and p-type Si/SiOx/Pd electrodes support the predictions of the metal/semiconductor interface model. However, at high light intensity (34 mW cm-2), the results of p-type Si/SiOx/Pd electrodes are found to be in agreement with the metal/solution interface model. The dependence of the photocurrent change on light intensity suggests that the magnitude of the surface recombination rate constant is important in locating the rate-determining step in the photoelectrochemical system. © 1990.