The long-term photocatalytic stability of Co2+-modified P25-TiO2 powders for the H2 production from aqueous ethanol solution

In this paper, the long-term stability of photocatalytic activity of Co2+ doped P25-TiO2 nanoparticles for hydrogen production from aqueous ethanol solution is discussed using a photoelectrochemical method in detail. It was found that after a long-term photoreaction, the photocatalytic activity of Co2+ ion modified P25-TiO2 photocatalyst for hydrogen production has decreased by a factor of ca. 50%, and still was very high compared to that of pure P25-TiO2 photocatalyst. And the steady anodic photocurrent appeared to have an obvious decrease after photoreaction (from 2.75 × 10−4 to 1.5 × 10−4 A), but the character of photocurrent response was still similar to photoreaction before. Moreover, the most important reason for the decrease of photocatalytic activity is the removal of CoOx active species (x > 1) from the surface of TiO2 photocatalyst after a long-term photoreaction. In addition, a new CoOx intermediate species (x < 1, photooxidative potential at −0.36 V versus SCE) emerged on the surface of TiO2 photocatalyst during photoreaction.