Brian Zutter1,Zejie Chen2,Aliya Lapp1,Kenta Watanabe3,Luisa Barrera4,Austin Bhandarkar1,Akihiko Kudo3,Rohini Bala Chandran4,Shane Ardo2,A. Talin1
Sandia National Laboratories1,University of California, Irvine2,Tokyo University of Science3,University of Michigan–Ann Arbor4
Brian Zutter1,Zejie Chen2,Aliya Lapp1,Kenta Watanabe3,Luisa Barrera4,Austin Bhandarkar1,Akihiko Kudo3,Rohini Bala Chandran4,Shane Ardo2,A. Talin1
Sandia National Laboratories1,University of California, Irvine2,Tokyo University of Science3,University of Michigan–Ann Arbor4
Solar-powered water splitting using nanoparticle photocatalyst suspensions is a promising route to economical, clean hydrogen production. In the Z-scheme approach, hydrogen and oxygen-evolving photocatalysts, such as SrTiO<sub>3</sub>:Rh and BiVO<sub>4</sub>, are coupled with a redox mediator to improve light absorption compared to single-photocatalyst systems. A key step in the water-splitting process is the separation and transport of photo-excited electrons and holes to the photocatalyst surface. Here we characterize charge transport in individual SrTiO<sub>3</sub>:Rh and BiVO<sub>4 </sub>nanoparticles using a nanoprobe within a scanning electron microscope, and directly map internal electric fields with electron-beam induced current. Charge transport in SrTiO<sub>3</sub>:Rh particles is limited by bulk defect states within the nanoparticle, in contrast to nearly Ohmic conduction in BiVO<sub>4</sub> nanoparticles. SrTiO<sub>3</sub>:Rh particles contain insignificant built-in E fields, while BiVO<sub>4</sub> nanoparticles contain built-in E field between different facets of the nanoparticle which can efficiently separate e-h pairs. Inefficient charge transport and lack of built-in electric field explain why the H<sub>2</sub>-evolving SrTiO<sub>3</sub>:Rh nanoparticles are the limiting component within this Z-scheme system.