Understanding performance and stability of photoelectrode interfaces

Abstract

Photoelectrochemical cells (PECs) hold great promise as an environmentally friendly method of conver􀆟ng sunlight into energy-dense chemicals. For example, the PEC approach can find applica􀆟on in the synthesis of mul􀆟-carbon-based hydrocarbons (C2+) by solar driven reduc􀆟on of carbon dioxide (CO2R), and in the genera􀆟on of hydrogen by solar water spli􀆫ng. However, the (photo)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 characteriza􀆟on techniques that can help to quan􀆟fy the performance and stability of photoelectrode surfaces with nanometer resolu􀆟on, using, as a model system, thin films of TiO2 deposited for corrosion protec􀆟on by atomic layer deposi􀆟on (ALD). A detailed analysis of Kelvin probe force microscopy (KPFM) measurements under intermitent illumina􀆟on allows us to analyze the evolu􀆟on of surface poten􀆟al over 􀆟me and extract localized 􀆟me constants for carrier dynamic processes on the surface. Furthermore, using operando spectroscopic ellipsometry (SE), we can directly quan􀆟fy the intrinsic stability of these protec􀆟ve overlayers under PEC water spli􀆫ng condi􀆟ons, par􀆟cularly as a func􀆟on of the degree of crystallinity of the TiO2 film. In addi􀆟on, we show several different device architectures with different degree of stability, spanning from GaN cotaings on Si for H2 produc􀆟on to ZnTe for CO2 reduc􀆟on. Understanding photoelectrodes at the nanoscale allows the systema􀆟c improvement of photoelectrode stability.