Understanding performance and stability of photoelectrode interfaces

Abstract

Photoelectrochemical cells (PECs) hold great promise as an environmentally friendly method of converting sunlight into energy-dense chemicals. For example, the PEC approach can find application in the synthesis of multi-carbon-based hydrocarbons (C2+) by solar driven reduction of carbon dioxide (CO2R), and in the generation of hydrogen by solar water splitting. However, the electrochemical environment poses significant challenges to the performance and stability of semiconductor based photoelectrodes. Tackling these challenges requires careful understanding of the behaviour of photoelectrode interfaces at the microscopic scale. Here we show examples of characterization techniques that can help to quantify the performance and stability of photoelectrode surfaces with nanometer resolution, using, as a model system, thin films of TiO2 deposited for corrosion protection by atomic layer deposition (ALD). A detailed analysis of Kelvin probe force microscopy (KPFM) measurements under intermitent illumination allows us to analyze the evolution of surface potential over time and extract localized time constants for carrier dynamic processes on the surface. Furthermore, using operando spectroscopic ellipsometry (SE), we can directly quantify the intrinsic stability of these protective overlayers under PEC water splitting conditions, particularly as a function of the degree of crystallinity of the TiO2 film. We will also provide examples of stable photoelectrodes based on Si/GaN and ZnTe for H2 production and CO2 photoelectroreduction, respectively.