The detailed descriptions for the fabrication of BiVO4 and Mo-BiVO4/CoPOM films are given in the ESI †. The fabrication protocols (incl. doping concentration and co-catalyst loading) were optimized by screening for the highest photoelectrocatalytic activity in each case. In short, the BiVO4 and Mo-BiVO4 films were prepared via spin coating onto FTO glass substrates, followed by drying and calcination. The CoPOM complex was synthesized according to a previously reported method, and deposited via impregnation to obtain Mo-BiVO4/CoPOM photoelectrodes. The X-ray diffraction (XRD) patterns of all BiVO4-based photoanodes exhibit the typical diffraction peaks of monoclinic scheelite BiVO4 (Fig. ), indicating that the crystal structure of BiVO4 is not significantly altered upon Mo-doping or deposition of CoPOM. No shifts of diffraction peaks or new reflexes related to molybdenum oxide were detected, which suggests that Mo is present in low amount as a homogenously distributed dopant without affecting the structure of BiVO4. As expected, as the amount of deposited CoPOM was very low, it could be detected neither in XRD nor by Fourier-transform infrared spectroscopy (FT-IR) (Fig. ). However, the presence of CoPOM in Mo- BiVO4/CoPOM was verified by transmission electron microscopy, energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) (see below).