title: C=C π Bond Modified Graphitic Carbon Nitride Films for Enhanced Photoelectrochemical Cell Performance.
abstract: Applications of graphitic carbon nitride (g-CN) in photoelectrochemical and optoelectronic devices are still hindered due to the difficulties in synthesis of g-CN films with tunable chemical, physical and catalytic properties. Herein we present a general method to alter the electronic and photoelectrochemical properties of g-CN films by annealing. We found that N atoms can be removed from the g-CN networks after annealing treatment. Assisted by theoretical calculations, we confirm that upon appropriate N removal, the adjacent C atoms will form new C=C π bonds. Detailed calculations demonstrate that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are located at the structure unit with C=C π bonds and the electrons are more delocalized. Valence band X-ray photoelectron spectroscopy spectra together with optical absorption spectra unveil that the structure changes result in the alteration of the g-CN energy levels and position of band edges. Our results show that the photocurrent density of the annealed g-CN film is doubled compared with the pristine one, thanks to the better charge separation and transport within the film induced by the new C=C π bonds. An ultrathin TiO2film (2.2 nm) is further deposited on the g-CN film as stabilizer and the photocurrent density is kept at 0.05 mA cm-2at 1.23 V versus reversible hydrogen electrode after two-cycle stability assessment. This work enables the applications of g-CN films in many electronic and optoelectronic devices.
authors.affiliation: Department of Physics and Materials Science and Centre for Functional Photonics (CFP), City University of Hong Kong, No. 83, Tat Chee Avenue, Kowloon, Hong Kong Special Administrative Region (SAR), China.|Shenzhen Research Institute, City University of Hong Kong, Shenzhen, China.|Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, 14469, Potsdam, Germany.
authors.forename: Juncao
authors.identifier: http://orcid.org/0000-0003-1792-6988
authors.initials: J
authors.lastname: Bian
authors.affiliation: Institute Solar Fuels and Operando Characterization of Solar Fuel Materials (EE-NOC), Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489, Berlin, Germany.
authors.forename: Lifei
authors.initials: L
authors.lastname: Xi
authors.affiliation: Department of Physics and Materials Science and Centre for Functional Photonics (CFP), City University of Hong Kong, No. 83, Tat Chee Avenue, Kowloon, Hong Kong Special Administrative Region (SAR), China.|Shenzhen Research Institute, City University of Hong Kong, Shenzhen, China.
authors.forename: Jianfu
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China.
authors.forename: Ze
authors.initials: Z
authors.lastname: Xiong
authors.affiliation: Department of Physics and Materials Science and Centre for Functional Photonics (CFP), City University of Hong Kong, No. 83, Tat Chee Avenue, Kowloon, Hong Kong Special Administrative Region (SAR), China.|Shenzhen Research Institute, City University of Hong Kong, Shenzhen, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Huang
authors.affiliation: Institute Solar Fuels and Operando Characterization of Solar Fuel Materials (EE-NOC), Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489, Berlin, Germany.
authors.forename: Kathrin M
authors.initials: KM
authors.lastname: Lange
authors.affiliation: Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China.
authors.forename: Jinyao
authors.initials: J
authors.lastname: Tang
authors.affiliation: Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, 14469, Potsdam, Germany.|Department of Chemistry, Ben Gurion University of the Negev, Rager Boulevard 1, Beer-Sheva, Israel.
authors.forename: Menny
authors.initials: M
authors.lastname: Shalom
authors.affiliation: Department of Physics and Materials Science and Centre for Functional Photonics (CFP), City University of Hong Kong, No. 83, Tat Chee Avenue, Kowloon, Hong Kong Special Administrative Region (SAR), China.|Shenzhen Research Institute, City University of Hong Kong, Shenzhen, China.
authors.forename: Rui-Qin
authors.initials: RQ
authors.lastname: Zhang
keywords: annealing; electron delocalization; graphitic carbon nitride films; photoelectrochemical cell; pi bonds