In Situ Reactive Imaging of Photoassisted Water Splitting Reaction Intermediates on n-Doped Strontium Titanate Using Surface Interrogation Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) gives spatially resolved information about electrochemical reactions occurring on surfaces, and easily probes reaction mechanisms. The in situ surface study of photoelectrochemical processes, such as water splitting at semiconductor electrodes, is challenging due to its fast kinetics and the multiple reactive intermediates formed. By combining the surface interrogation mode (SI-) of SECM ^[1] with transport simulations, the reactivity of multiple adsorbed intermediates resulting from water splitting on gently n-doped strontium titanate (STO) was investigated.  Using this technique, we addressed the in situ detection of long lived holes and photogenerated hydroxyl radical on STO. Combined with the measurements on the local production of oxygen using the collection mode of SECM, our methodology provides an integrated view of reactivity at photocatalytic surfaces.

In our SI-SECM measurements, a micro- or nano-electrode used as SECM tip was positioned close to the STO surface and activated to generate a redox titrant that provided information about the surface coverage and reaction kinetics of adsorbed intermediates. By addressing different parts on the electrode surface, it is possible to obtain information about different surface condition son the STO electrode. This combined methodology brings spatial resolution to SI-SECM, and measured different adsorbate coverage on pristine and defective STO (100) surfaces. For the first time, SI-SECM was adapted to the reactive imaging of adsorbates to show how these affect photocatalytic performance on a heterogeneous surface.

[1] Rodríguez-López, J. The Surface Interrogation Mode of Scanning Electrochemical Microscopy (SI-SECM): an approach to the study of adsorption and (electro)catalysis at electrodes. In Electroanalytical Chemistry, a series of advances. Vol. 24. Bard, A.J. and Zoski, C.G., Eds. 2012, CRC Press, pp. 287-352.