DSA-type Ti/Ru x Sn 1-x O 2 electrodes were prepared by thermal decomposition method as photoelectrocatalysts (PECs) and extensively characterized by various sophisticated techniques. First-principles calculations was employed to study the effects of Ru content on the electronic structures of the Ru x Sn 1-x O 2 coatings. The photoelectric-synergistic catalytic activity of the Ti/Ru x Sn 1-x O 2 electrodes was evaluated for the degradation of methyl orange (MO) in aqueous solution. The results show that the RuO 2 − SnO 2 solid solution could be formed. The band gaps of the Ru x Sn 1-x O 2 coatings gradually decreased and eventually turned into metallic conductivity with the increase of ruthenium content. As a PEC electrode, reducing band gap is helpful to improve electronic conductivity and the electrocatalytic activity, but not always advantageous to increase the photocatalytic activity. Because too narrow band gap will sacrifice the photogenerated charge carriers and thus reduce photocatalytic activity of the electrode. In our experiments, the rate constant of Ti/Ru 0.05 Sn 0.95 O 2 electrode increased with increasing Ru content and exhibited the maximum rate for 5% Ru loading. The stability test showed the photoelectrocatalytic activity of the Ti/Ru 0.05 Sn 0.95 O 2 electrode almost had no attenuation after 100 h photoelectrolysis, revealing that this electrode has good long-term stability. [ABSTRACT FROM AUTHOR]