Brian Zutter1,Zejie Chen2,Luisa Barrera3,Aliya Lapp1,Austin Bhandarkar1,William Gaieck2,Kenta Watanabe4,Akihiko Kudo4,Daniel Esposito5,Rohini Chandran3,Shane Ardo2,A. Talin1
Sandia National Laboratories1,University of California, Irvine2,University of Michigan–Ann Arbor3,Tokyo University of Science4,Columbia University5
Brian Zutter1,Zejie Chen2,Luisa Barrera3,Aliya Lapp1,Austin Bhandarkar1,William Gaieck2,Kenta Watanabe4,Akihiko Kudo4,Daniel Esposito5,Rohini Chandran3,Shane Ardo2,A. Talin1
Sandia National Laboratories1,University of California, Irvine2,University of Michigan–Ann Arbor3,Tokyo University of Science4,Columbia University5
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 photocarrier diffusion lengths with electron-beam induced current. Charge transport in SrTiO<sub>3</sub>:Rh particles is space-charge limited by bulk Rh<sup>4+</sup> defect states within the nanoparticle, in contrast to nearly Ohmic (band) conduction in BiVO<sub>4</sub> nanoparticles. Photogenerated e-h pairs diffuse less than 10 nm before recombining within SrTiO<sub>3</sub>:Rh particles due to the high concentration of Rh traps (1%), whereas band conduction in BiVO<sub>4</sub> particles allows for photocarrier diffusion lengths in excess of 400 nm. Inefficient charge transport explains why the H<sub>2</sub>-evolving SrTiO<sub>3</sub>:Rh nanoparticles are the limiting component within this Z-scheme system.