TiO_2-polyheptazine hybrid photoanodes: Effect of cocatalysts and external bias on visible light-driven water splitting

摘要

Photoanodes based on TiO_2-polyheptazine (T1O2-PH) hybrids are, due to the energetics of photogenerated charges, very promising for solar water splitting in terms of possibly reduced need for external electric bias. Visible (λ > 420 nm) light-driven photooxidation of water at TiO_2-PH electrodes loaded with two different metal oxide cocatalysts was investigated. As compared with TiO_2-PH photoanodes loaded with colloidal [iridium (IV) oxide] IrO_2 deposited by colloidal deposition, photoelectrodes modified with CoO_x oxygen-evolving cocatalyst (Co-Pi) deposited by photoassisted deposition precipitation method showed both higher photocurrents and more efficient oxygen evolution under prolonged irradiation. The minimum external electric bias needed to observe complete photooxidation of water to dioxygen at TiO_2-PH photoanodes modified with Co-Pi was estimated to be ～0.6 V at pH 7. The key factor limiting the photoconversion efficiency at low bias potentials is the fast primary recombination of photogenerated charges.