It is known that PEI can be protonated in a wide pH range (pH 3-10) when dissolved in aqueous solutions. The positively charged cationic PEI thus plays a role of an electrostatic linker between CNx and CoPOM that are both charged negatively. For comparison, the CNx-TiO2 electrodes were also only dipped into the CoPOM solution resulting in the reference, linker-free electrodes CoPOM-CNx-TiO2. To evaluate and compare the CoPOM loading of the two CoPOM-containing CNx-TiO2 electrodes, energy dispersive X-ray (EDX) spectra were recorded. The CoPOM-PEI-CNx-TiO2 electrode shows significantly higher concentration of elements contained in CoPOM, with 0.35 at% Co, 0.13 at% P and 0.97 at% W, compared to 0.05 at% Co, 0.07 at% P and 0.03 at% W in case of the PEI-free CoPOM-CNx-TiO2 reference electrode (Supporting Information, Fig. ). The higher CoPOM loading of CoPOM-PEI-CNx-TiO2 was further corroborated by XPS, showing the increase of surface concentration of Co by the factor of 3.4 in photoelectrodes comprising the PEI linker (Supporting Information, Figure ). In addition, the EDX mapping (Supporting Information, Fig. ) depicts the homogeneous distribution of CoPOM within the porous CNx-TiO2 structure. Finally, only in case of CoPOM-PEI-CNx-TiO2, the characteristic IR fingerprint of CoPOM is detectable (Fig. ), which confirms improved CoPOM immobilization compared to electrodes without the cationic PEI linker. We conclude that the more effective immobilization of CoPOM in the CoPOM-PEI-CNx-TiO2 photoanodes is due to beneficial effect of the electrostatic attraction between the positively charged PEI linker and the negatively charged CNx and CoPOM components.