Ferroelectric polarization-enhanced charge separation in quantum dots sensitized semiconductor hybrid for photoelectrochemical hydrogen production

A major unresolved challenge in photoelectrochemical (PEC) solar fuels production is the efficient separation of charges. Here we successfully synthesized a hybrid ferroelectric-semiconducting TiO2 system as photoanode, sensitized with colloidal quantum dots (QDs) to enhance light absorption. By tuning the amount of barium titanate (BaTiO3, BTO) in the photoanode composition and its polarization state, we could obtain a remarkable enhancement up to + 105% compared to the simple TiO2 photoanode. By using engineered QDs with a gradient interface, the photoanode reached a photocurrent density (Jph) and charge-separation efficiency (ηseparation) of 15.3 mA cm−2 and 22.3% at 0.5 V versus the reversible hydrogen electrode (RHE), respectively. To investigate the general beneficial effect of the addition of BTO, three different kinds of QDs were used. By systematically investigating UV–Visible absorption and band alignment, we were able to attribute the increased Jph to an improved charge separation, which was induced by the ferroelectric depolarization electric field. The results were further confirmed by photoluminescence and electrochemical impedance spectroscopy measurements. Our work provides unique insights to improve the performance of PEC photoelectrodes by combining ferroelectric and semiconducting features with the broad absorption of colloidal QDs.