  Photoelectrochemical water splitting is a promising route to produce hydrogen
from solar energy. However, corrosion of semiconducting photoelectrodes remains
a fundamental challenge for their practical application. The stability of
BiVO4, one of the best performing photoanode materials, is systematically
examined here using an illuminated scanning flow cell to measure its
dissolution operando. The dissolution rates of BiVO4 under illumination depend
on the electrolyte and decrease in the order: borate (pH=9.3) > phosphate
(pH=7.2) > citrate (pH=7.0). BiVO4 exhibits an inherent lack of stability
during the oxygen evolution reaction (OER), while hole-scavenging citrate
electrolyte offers kinetic protection. The dissolution of Bi peaks at different
potentials than the dissolution of V in phosphate buffer, whereas both ions
dissolve simultaneously in borate buffer. The life cycle of a 90 nm BiVO4 film
is monitored during one hour of light-driven OER in borate buffer. The
photocurrent and dissolution rates show independent trends with time,
highlighting the importance to measure both quantities operando. Dissolution
rates are correlated to the surface morphology and chemistry characterized
using electron microscopy, X-ray photoelectron spectroscopy and atom probe
tomography. These correlative measurements further the understanding on
corrosion processes of photoelectrodes down to the nanoscopic scale to
facilitate their future developments.
