Enhanced photocatalytic hydrogen production from water - methanol solution by nickel intercalated into titanate nanotube

Nickel-intercalated titanate nanotube was hydrothermally synthesized and evaluated for photocatalytic hydrogen production from methanol-water solution under UV light irradiation. The nickel intercalated into the nanotube was present as a hydrated Ni complex of [Ni_x ^II(OH) _2x-1(OH₂)]⁺ and was responsible for a dramatic enhancement of hydrogen evolution rate relative to that of titanate nanotube itself. The nickel species in the interlayer provided active sites for proton reduction and caused fast diffusion of photoelectrons generated from titanate layers toward the nickel sites, leading to a high photocatalytic activity. Upon annealing at 400 °C, the hydrated nickel complex was partly converted to NiO and the hydrogen evolution rate was reduced, indicating that the nickel hydroxide was a more efficient cocatalyst for titanate nanotube. A high and stable photocurrent generation was also observed from a film made of the nickel-intercalated titanate nanotube immersed in a NaOH solution.