Contrasting transient photocurrent characteristics for thin films of vacuum-doped "grey" TiO2 and "grey" Nb2O5

Author(s)

de Araujo, Moises A. ; Gromboni, Murilo F. ; Marken, Frank ; Parker, Stephen C. ; Peter, Laurence M. ; Turner, Josh ; Aspinall, Helen C. ; Black, Kate ; Mascaro, Lucia H.

• Document type: Journal article
• Source: APPLIED CATALYSIS B-ENVIRONMENTAL; v. 237, p. 14-pg., 2018-12-05.

Abstract

Photo-catalytic performance for oxide films, here for inkjet-printed TiO2 (ca. 1 mu m thickness on PTO) and for spray-pyrolysis-coated Nb2O5 (ca. 1 mu m thickness on PTO), is affected by oxygen vacancies that form during vacuum-heat treatment at 550 degrees C. The effects of the oxygen vacancies are associated with formation of Ti(III) and Nb(IV) sites, respectively, and therefore optically visible as "grey" coloration. Photo-electrochemical light-on-off transient experiments are performed in the limit of thin film photoanodes, where front and back illumination result in the same photo-current responses (Le. with negligible effects from internal light absorption gradients). It is shown that generally the magnitude of photo-currents correlates linearly with light intensity, which is indicative of dominant "photo-capacitive" behaviour. At an applied voltage of 0.4 V vs. SCE (in the plateau region of the photo-current responses) the potential and also the pH (going from 1.0 M KOH to 0.1 M HClO4 in the presence of methanol quencher) have no significant effect on photo-currents; that is, surface chemical/kinetic effects appear to be unimportant and interfacial hole transfer may be rate limiting. Under these conditions (and based on a simplistic mechanistic model) changes in photo-currents introduced by oxygen vacancy doping (detrimental for TiO2 and beneficial for Nb2O5) are assigned primarily to changes in electron mobility. (AU)

• FAPESP's process: 16/12681-0 - Preparation and characterization of ternary sulfide semiconductor thin films of antimony and tin, TAS (T = tin, antimony and A = S = sulfur), for use in photovoltaic cells
• Grantee: Moisés Albuquerque de Araújo
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 14/50249-8 - Green chemistry: sustainable synthetic methods employing benign solvents, safer reagents, and bio-renewable feedstock
• Grantee: Arlene Gonçalves Corrêa
• Support Opportunities: Research Grants - Research Centers in Engineering Program
• FAPESP's process: 13/07296-2 - CDMF - Center for the Development of Functional Materials
• Grantee: Elson Longo da Silva
• Support Opportunities: Research Grants - Research, Innovation and Dissemination Centers - RIDC