Charge Transfer Processes at WSe2 Electrodes with pH‐Controlled Stability

In aqueous solutions of low pH, the energy bands at the surface of n-WSe{sub 2} become unpinned upon illumination. The corresponding positive shift of bands is caused by accumulation of holes at the surface. This is understood as being due to a position of the corrosion potential positive of the valence band, which moves in a more negative direction with increasing pH. In acid solutions, the energy bands remain pinned under illumination in the presence of redox systems which have a standard potential located at or negative of the valence bandedge. Experiments with rotating ring disk electrodes have shown that in this case the electrode is completely stable. This is a very promising result with respect to regenerative solar cells, because for the first time a stabilization by a redox couple with a standard redox potential near the valence bandedge of a photocorroding n-type semiconductor was found. The charge transfer processes at n- and p-type electrodes are analyzed in detail in solutions of different pH.