Enhanced photoelectrochemical water splitting on hematite thin film with layer-by-layer deposited ultrathin TiO2 underlayer

Hematite has attracted numerous scrutiny for photoelectrochemical water splitting using visible light because of its suitable band gap value and excellent stability in aqueous solution. Herein we report that ultrathin TiO2 underlayers, prepared by layer-by-layer deposition of highly crystallized titanate nanosheets (∼0.7 nm thick) followed with calcination, perform well on enhancing photoelectrochemical property of hematite film. The ultrathin TiO2 underlayers, made from 1 to 5 layers of titanate nanosheets, significantly shift the photocurrent onset to 0.9 V vs. RHE, ca. 0.6 V more negative than in the absence of TiO2 underlayer, and meanwhile increases photocurrent greatly. The ∼1.4 nm thick TiO2 underlayer, made from two layers of titanate nanosheets performs the best in the series of samples and increases the photocurrent of hematite films from 9.1 to 373 μA cm−2 at 1.23 V vs. RHE. The enhancement mechanism is attributed to the blocking effect of TiO2 underlayer, which could significantly suppress the electron back injection from SnO2:F electrode to hematite and consequently promote the separation efficiency of photogenerated charge carriers in hematite films.