A Photoelectrochemical Device with Dynamic interface Energetics: Understanding of Structural and Physical Specificities and Improvement of Performance and Stability

Abstract

The basic configuration of a photoelectrochemical (PEC) water splitting device contains a semiconductor junction, which separates charge carriers by developing interface energetics. Recently, porous metal oxide/semiconductor junctions have shown that flat‐band potentials (Vfb), representing interface energetics, could be dynamically changed with PEC reactions. However, it remains unclear as to what structural and physical specificities of the porous metal oxide induce the dynamic Vfb. Herein, it is demonstrated that the electrolyte permeability and nanocrystal structure of porous NiOx are crucial for the dynamic Vfb in porous NiOx integrated Si photocathodes. A comparison of the dense and porous NiOx with electrolyte impermeable and permeable features, respectively, shows that Vfb changes only in the porous NiOx. The porous NiOx also exhibits a nanocrystal structure and increased Vfb values with a decrease in nanocrystal size. As a result of the increased Vfb, the porous NiOx achieves much higher PEC performance compared to that of the dense NiOx. However, electrolyte permeability causes electrochemical decomposition of the Si component. Thus, a cointegration of the porous and dense NiOx bilayers, which ensures stable PEC operation for 10 h while achieving high potentials of 0.2 V versus reversible hydrogen electrode at a photocurrent of 10 mA cm−2, is proposed.