The photoanodes made of Cd0.3Zn0.7S and FTO were prepared and modified by Ni(OH)2, Zn(OH)2, and NiS as co-catalysts. The amounts of the co-catalysts were the same as those in the most active photocatalysts tested earlier in photocatalytic hydrogen production. The obtained electrodes were studied by X-ray diffraction and photoelectron spectroscopy, scanning and transmission electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The modification of the photoelectrode surface led to the growth of short-circuit current density, power conversion efficiency and photogenerated charge carriers lifetime, while open-circuit voltage, fill factor, and resistivity fell. The changes in the photocatalytic activity and the photoelectrochemical properties of the tested samples were found to correlate with each other, which indicated the same origin of the studied phenomenon.