The electronic structure analysis provides insights into the stability, reactivity, and potential applications of the Chini clusters, with size-dependent properties playing a leading role. Not only the photochemical properties, such as the position of the electron absorption band, but also electron and hole transport properties change in line with their nuclearity number n. The reactivity of the Chini clusters towards the H and H2 species was also probed. Our calculations indicate that these systems may be considered as components of the catalytic materials used for hydrogen generation. These assumptions were confirmed by testing the Chini-TiO2 composites in the photocatalytic H2 generation from water -methanol mixture.