The reactivity of photoelectrochemical interfaces is susceptible to the presence of surface and bulk chemical and structural perturbations. The need to understand their impact has become invigorated by the interest in plasmonics, co-catalysis, defects and bandgap engineering. Here we describe the spatially-resolved exploration of water oxidation anodes via a powerful toolset based on scanning electrochemical microscopy (SECM) for the identification of reactive features and the quantification of surface reactivity descriptors. Using a combination of product collection modes (O2, H2O2), redox mediator-based measurements, and transient redox titrations we are gaining quantitative insight into the role of local perturbations in conditioning, controlling and encoding reactivity on photoelectrochemical interfaces. In a first application, we will describe the direct measurement of plasmonic enhancements via sub-surface Al nano-dimers fabricated with precise control below a TiO2 photoanode. SECM in the collection mode enabled the imaging and correlation of O2 evolution rates with modified regions, as well as the confirmation of plasmonic effects via polarization-dependent studies, and the imaging and quantification of enhancements on small areas that would be difficult to detect using macroscopic tools. In a second application, we will discuss the use of Surface Interrogation SECM (SI-SECM) for obtaining information about individual surface defects. Using fully matched experiments to numerical analysis methods developed in our laboratory, we obtained the surface coverage and reaction dynamics of adsorbed reactive oxygen species (aROS) and photogenerated holes on lightly n-doped single crystal strontium titanate (SrTiO3) electrodes. We further introduced the use of this technique using nano-SECM probes. New in situ methods capable of elucidating the surface dynamics of operating photocatalysts are required to provide a new leap in the design of photochemical interfaces for environmental and energy applications.

Imaging and quantifying the reactivity of chemical and structural perturbations on operating water oxidation photoanodes

253rd National Meeting (2017)

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