title: On the nature of defect states in tungstate nanoflake arrays as promising photoanodes in solar fuel cells.
abstract: An electrochemical method is presented to study the nature of the defect states in sub-stoichiometric tungsten oxide nanoflake photoanodes used in water splitting. First, stoichiometric/sub-stoichiometric tungstate nanoflake arrays were deliberately developed via annealing under different atmospheres (air, O2, and H2) in different sequences. UV-Vis diffuse reflectance spectra and Tauc analysis indicated the presence of oxygen vacancies, which was also confirmed via XRD and Raman analysis, with samples annealed in an air/O2 sequence resulting in the most stoichiometric monoclinic structures. A defect sensitivity factor was proposed to explain the nature of defects whether they are deep or shallow. Mott-Schottky analysis was used to confirm the expected defect donor densities, as well as to confirm the nature of the developed oxygen vacancy defect states. The tungstate photoanodes were tested in photoelectrochemical water splitting cells and their photoconversion efficiency was demonstrated and discussed in detail.
authors.affiliation: Energy Materials Laboratory (EML), School of Sciences and Engineering, The American University in Cairo, New Cairo 11835, Egypt. nageh.allam@aucegypt.edu.
authors.forename: Aya M
authors.initials: AM
authors.lastname: Mohamed
authors.affiliation: Energy Materials Laboratory (EML), School of Sciences and Engineering, The American University in Cairo, New Cairo 11835, Egypt. nageh.allam@aucegypt.edu.
authors.forename: Ahmad W
authors.initials: AW
authors.lastname: Amer
authors.affiliation: Department of Chemistry and Earth Sciences, College of Arts and Sciences, Qatar University, P.O. Box 2713, Doha, Qatar.
authors.forename: Siham Y
authors.initials: SY
authors.lastname: AlQaradawi
authors.affiliation: Energy Materials Laboratory (EML), School of Sciences and Engineering, The American University in Cairo, New Cairo 11835, Egypt. nageh.allam@aucegypt.edu.
authors.forename: Nageh K
authors.initials: NK
authors.lastname: Allam