Design Guidelines of Insulator for Improving Stability and Performance of Nanoelectrocatalyst/Insulator/Semiconductor Photoelectrochemical Cells

Abstract

Electrocatalyst/insulator/serniconductor configurations have been considered as promising designs for efficient photoelectrochemical (PEC) water-splitting reactions. However, the roles and effects of the insulator on the PEC reactions have not been clearly understood, in particular, for the nanoelectrocatalyst integrated semiconductor. In this study, we investigated the effects and ability of insulator material and thickness in terms of the stability and performance for PEC alkaline water reduction reaction by integrating nanocrystalline NiOx electrocatalyst/insulator/p-Si photocathodes. This was clearly understood by comparing the stability and performance of amorphous TiOx and SiO2. We demonstrated that the a-TiOx with low barrier height for electron transfer relative to that for hole transfer shows the ability for selective collection of photogenerated minority charge (electron) carriers. This enables a high open circuit potential while minimizing the kinetic overpotential required for electron transfer. The a-TiOx also renders excellent passivation ability for the Si surface defects, minimizing the recombination loss. In addition to these PEC performance improvements, the ability to protect completely the Si surface against corrosive electrolyte permeating through the nanocrystalline NiOx ensures long-term stability. All these abilities were maximized by optimizing the thickness of the a-TiOx (10 nm), thereby enabling the sustainable generation of a photocurrent of 10 mA/cm(2) at a high potential level of 0.3 V (vs reversible hydrogen electrode). These results present design guidelines for the insulator along with methods to determine the effects of the insulator on PEC responses.