In a recent publication (Melo Jr. and coworkers, Nano Lett., Article ASAP, http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.7b04020) the Osterloh Lab used Surface Photovoltage Spectroscopy (SPS) to measure the photopotential across a Ru–SrTiO3:Rh/BiVO4 particle tandem photocatalyst for the first time.