title: Templating Sol-Gel Hematite Films with Sacrificial Copper Oxide: Enhancing Photoanode Performance with Nanostructure and Oxygen Vacancies.
abstract: Nanostructuring hematite films is a critical step for enhancing photoelectrochemical performance by circumventing the intrinsic limitations on minority carrier transport. Herein, we present a novel sol-gel approach that affords nanostructured hematite films by including CuO as sacrificial templating agent. First, by annealing in air at 450 °C a film comprising an intimate mixture of CuO and Fe2O3 nanoparticles is obtained. The subsequent treatment with NaCl and annealing at 700 °C under Argon reveals a nanostructured highly crystalline hematite film devoid of copper. Photoelectrochemical investigations reveal that the incorporation of CuO as templating agent and the inert conditions employed during the annealing play a crucial role in the performance of the hematite electrodes. Mott-Schottky analysis shows a higher donor concentration when annealing in inert conditions, and even higher when combined with the NaCl treatment. These findings agree well with the presence of an oxygen-deficient shell on the material's surface evidenced by FT-IR and XPS measurements. Likewise, the incorporation of the CuO enhances the photocurrent obtained at 1.23 V from 0.55 to 0.8 mA·cm(-2) because of an improved nanostructure. Optimized films demonstrate an incident photon-to-current efficiency (IPCE) of 52% at 380 nm when applying 1.23 V versus RHE, and a faradaic efficiency for water splitting close to unity.
authors.affiliation: †Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin Key Laboratory of Applied Catalysis Science and Technology, State Key Laboratory of Chemical Engineering (Tianjin University), School of Chemical Engineering, Tianjin University, Tianjin 300072, China.|‡Laboratory for Molecular Engineering of Optoelectronic Nanomaterials, École Polytechnique Fédérale de Lausanne (EPFL), Station 6, 1015 Lausanne, Switzerland.
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.affiliation: ‡Laboratory for Molecular Engineering of Optoelectronic Nanomaterials, École Polytechnique Fédérale de Lausanne (EPFL), Station 6, 1015 Lausanne, Switzerland.
authors.forename: Néstor
authors.initials: N
authors.lastname: Guijarro
authors.affiliation: †Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin Key Laboratory of Applied Catalysis Science and Technology, State Key Laboratory of Chemical Engineering (Tianjin University), School of Chemical Engineering, Tianjin University, Tianjin 300072, China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Zhang
authors.affiliation: ‡Laboratory for Molecular Engineering of Optoelectronic Nanomaterials, École Polytechnique Fédérale de Lausanne (EPFL), Station 6, 1015 Lausanne, Switzerland.
authors.forename: Mathieu S
authors.initials: MS
authors.lastname: Prévot
authors.affiliation: ‡Laboratory for Molecular Engineering of Optoelectronic Nanomaterials, École Polytechnique Fédérale de Lausanne (EPFL), Station 6, 1015 Lausanne, Switzerland.
authors.forename: Xavier A
authors.initials: XA
authors.lastname: Jeanbourquin
authors.affiliation: ‡Laboratory for Molecular Engineering of Optoelectronic Nanomaterials, École Polytechnique Fédérale de Lausanne (EPFL), Station 6, 1015 Lausanne, Switzerland.
authors.forename: Kevin
authors.initials: K
authors.lastname: Sivula
authors.affiliation: §School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Chen
authors.affiliation: †Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin Key Laboratory of Applied Catalysis Science and Technology, State Key Laboratory of Chemical Engineering (Tianjin University), School of Chemical Engineering, Tianjin University, Tianjin 300072, China.
authors.forename: Yongdan
authors.initials: Y
authors.lastname: Li
keywords: copper oxide; hematite; photoelectrochemistry; sol−gel; water splitting