Semiconductor | Catalyst Interfaces in Photoelectrochemical Devices: Charge Transport Theory, Experimental Technique Development, and Nanoscale Applications

Abstract

Photoelectrochemical energy conversion is a promising method to harvest incident sunlight and convert/store the energy in stable hydrogen gas bonds. The process is reliant on coupling between a light-absorbing semiconductor and an electrocatalyst responsible for enhancing the oxygen/hydrogen evolution reaction. However, photoelectrochemical energy storage remains inefficient, in part because the semiconductor|catalyst interface is not well understood. Attaining a clearer understanding of the interface is critically important because it is responsible for separation and collection of photogenerated charge.

In the following dissertation the behavior of the semiconductor|catalyst interface is experimentally and theoretically analyzed. Chapter 1 introduces the reader to two experimental techniques which facilitate interfacial understanding: dual-working-electrode photoelectrochemistry and potential sensing electrochemical atomic force microscopy. These techniques enable direct observation of potential and current transport across the semiconductor|catalyst interface during device operation. Chapter 2 applies these techniques to examine two common electrochemical experimental methods. The results suggest that analyzing the semiconductor|catalyst interface with the two methods is more challenging than previously appreciated. Chapter 3 presents an analytical model describing charge transport across the semiconductor|catalyst interface. In Chapter 4 the experimental techniques from Chapter 1 are applied to analyze the semiconductor|catalyst behavior of two model systems with interfacial heterogeneity. The anomalously good performance of some devices is attributed to an increase in interfacial selectivity caused by the “pinch-off” effect.

This work builds upon and improves understanding of the semiconductor|catalyst interface in photoelectrochemical devices. The dissertation contains previously published and un-published co-authored materials.