Enhanced Photocatalytic H₂-Production Activity of TiO₂ by Ni(OH)₂ Cluster Modification

Abstract

Ni(OH)2 cluster-modified TiO2 (Ni(OH)2/TiO2) nanocomposite photocatalysts were fabricated by a simple precipitation method using Degussa P25 TiO2 powder (P25) as support and Ni(NO3)2 as precursor. The effect of Ni(OH)2 cluster loading content on the photocatalytic hydrogen production rates of the as-prepared samples in methanol aqueous solution was investigated. The results showed that the photocatalytic H2-production activity of TiO2 was significantly enhanced by loading Ni(OH)2 clusters. The optimal Ni(OH)2 loading content was found to be 0.23 mol %, giving a H2-production rate of 3056 μmol h−1 g−1 with quantum efficiency (QE) of 12.4%, exceeding that on pure TiO2 by more than 223 times. This high photocatalytic H2-production activity is due to the deposition of Ni(OH)2 clusters on the surface of TiO2. The enhanced mechanism is because the potential of Ni2+/Ni (Ni2+ + 2e− = Ni, Eo = −0.23 V) is slightly lower than conduction band (CB) (−0.26 V) of anatase TiO2, meanwhile higher than the reduction potential of H+/H2 (2H+ + 2e− = H2, Eo = −0.00 V), which favors the electron transfer from CB of TiO2 to Ni(OH)2 and the reduction of partial Ni2+ to Ni0. The function of Ni0 is to help the charge separation and to act as cocatalyst for water reduction, thus enhancing the photocatalytic H2-production activity.