Atomic force microscopy resolved semiconductor-electrolyte interface for photocatalytic water splitting

The semiconductor-electrolyte interface properties can have substantial impacts on the photocatalytic performance of semiconductors. However, they remain unexplored due to the lack of a suitable tool. In this thesis, we developed an AM-AFM based method to resolve semiconductor-electrolyte interface properties on individual faceted semiconducting NPs in situ and operando with sub-facet resolutions. For the first the time, the facet and pH dependent surface charge/potential, surface photo voltage were determined in electrolytes. The high-resolution advantage of AFM enabled us to corelate the distinct charge behaviour and photo responses to heterogeneous surface structure especially on the wide defect rich regions and narrow atomic steps. It also demonstrated adjusting the fluid composition can tune the interface properties; indirectly, it controlled the reactivity and behaviours of the nanoparticles. This highlighted the importance of the in-situ measurements. Besides, the atomic surface structures and hydration structures were imaged in one of our systems. Finally, to explore the effects of the fluid compositions effect on the real reactions, photo deposition reactions were performed at different electrolyte conditions, the size of the cocatalysts, the location of the deposition can be tuned. All of the results are unique and crucial for facet-dependent phenomena, such as facet-selective accumulation of photo-generated charge carriers and photo deposition in the photocatalysis field, and organic adsorption and particulate aggregation in the colloidal society. By quantifying the effects from facets, the electrolyte composition, and illumination, better control on these processes can be obtained, eventually, the catalytic performances of the semiconductors can be optimised. Here is the summary of the thesis.