We develop a method that can be used to qualitatively map photocurrent on photoelectrode surfaces, and show its utility for morphologically controlled W-doped BiVO4. The method is based on the deliberate photoinduced sintering of Au NPs, a photon-driven process that indicates oxidation with nanoscale-resolution. This strategy allows us to identify the active regions on W-doped BiVO4 photoelectrodes, and we observe a strong dependence of photoactivity on the electrode morphology, controlled by varying the relative humidity during the sol–gel fabrication process. We find that photoelectrode morphologies that exhibit the most evenly distributed Au sintering are those that yield the highest photoelectrochemical (PEC) activity. Understanding the correlation between electrode morphology and PEC activity is essential for designing structured semiconductors for PEC water splitting.