Empirical Analysis of the Photoelectrochemical Impedance Response of Hematite Photoanodes for Water Photo-Oxidation

TL;DR

This paper introduces an empirical DRT-based analysis method for PEIS spectra of hematite photoanodes, providing unbiased insights into water oxidation mechanisms without relying on prior assumptions.

Contribution

It presents a novel, assumption-free approach combining DRT analysis with circuit modeling to better understand photoelectrode behavior.

Findings

DRT analysis reveals key relaxation processes in hematite photoanodes.

The method uncovers the evolution of mechanisms with potential and electrolyte composition.

Identifies a common step in water and H2O2 oxidation reactions.

Abstract

Photoelectrochemical impedance spectroscopy (PEIS) is a useful tool for the characterization of photoelectrodes for solar water splitting. However, the analysis of PEIS spectra often involves a priori assumptions that might bias the results. This work puts forward an empirical method that analyzes the distribution of relaxation times (DRT), obtained directly from the measured PEIS spectra of a model hematite photoanode. By following how the DRT evolves as a function of control parameters such as the applied potential and composition of the electrolyte solution, we obtain unbiased insights into the underlying mechanisms that shape the photocurrent. In a subsequent step, we fit the data to a process-oriented equivalent circuit model (ECM) whose makeup is derived from the DRT analysis in the first step. This yields consistent quantitative trends of the dominant polarization processes observed. Our observations reveal a common step for the photo-oxidation reactions of water and H2O2 in alkaline solution