The morphology and film thickness of as-prepared BiVO4, Mo-BiVO4 and Mo-BiVO4/CoPOM photoanodes were investigated by field emission scanning electron microscopy (FESEM). As shown in Fig. , all of the films are composed of uniform and homogeneous worm-like nanoparticles with an average diameter of ~100-200 nm, forming a three-dimensional mesoporous structure with pore sizes in the range of tens of nanometers. The introduction of F-108 as a structural agent during the synthesis is responsible for inducing this porous architecture, which serves as the foundation for all subsequent surface-modified photoanodes. Notably, both Mo doping shown in Fig. and surface modification with CoPOM shown in Fig. have no appreciable effect on the morphology of BiVO4, retaining the typical porous structure. Fig. shows the cross-section SEM images of all three photoanodes, showing that the material layers have a comparable thickness of 600 ± 20 nm. Since the structure of the Mo-BiVO4 material is porous and the CoPOM was deposited via the impregnation method, a homogenous distribution of the co-catalyst throughout the porous layer is expected. To investigate the distribution of CoPOM, EDX elemental mapping was carried out. For both in the cross-section and the surface of Mo-BiVO4/CoPOM, the elements Mo, Bi, V and O (representing Mo-BiVO4) and Co, W (representing CoPOM) have been detected. These EDX mapping results demonstrate a very dense and uniform distribution of CoPOM within the mesoporous Mo-BiVO4 structure (Fig. and S2e †). A closer look with the help of high-resolution transmission electron microscopy (HRTEM) revealed that Mo-BiVO4/CoPOM contains uniformly distributed nanospheres with a diameter of less than 10 nm (Fig. and). Since these nanospheres are completely absent in the (CoPOM-free) Mo-BiVO4 photoanode (Fig. and), we assume the nanospheres to be CoPOM nanoparticles. These CoPOM nanospheres are closely spaced and homogeneously distributed on the surface of the Mo-BiVO4 porous support (Fig. and). Furthermore, Fig. In order to further verify the presence of CoPOM in the Mo-BiVO4/CoPOM and to investigate the surface chemical composition of the photoelectrode material, XPS analysis was carried out at BiVO4, Mo-BiVO4 and Mo-BiVO4/CoPOM electrodes. As shown in Fig. †, all expected signals of Mo, Bi, V, O, Na, Co and W elements are observed in the XP survey spectrum of Mo-BiVO4/CoPOM, which indicates the successful preparation of the composite material. Two typical spin-orbit coupling peaks of Bi (at 164.3 eV and 159.1 eV for Bi 4f5/2 and Bi 4f7/2, respectively) are assigned to Bi 3+ in BiVO4 (Fig. and S3b †). The O 1s XP spectrum (Fig. ) can be fitted to two peaks located at 529.8 eV and 530.7 eV, which are assigned to lattice oxygen in BiVO4 and surface hydroxyl oxygen, respectively. The vanadium signals (Fig. and) can be fitted into two spin-orbit coupling peaks located at 524.0 eV (V 2p1/2) and 516.6 eV (V 2p3/2), which are characteristic of V 5+ species in BiVO4.