Photoelectrochemical water splitting performed with semiconductor materials has attracted attention due to potential clean energy production, achievable utilizing light. In this context, TiO2 is the most investigated semiconductor, though characterized by i) low rate of photopromoted e- transfer and ii) high recombination rate of photoproduced charge carriers (e-/h+ pairs). Doping with non-metal elements is often suggested as a valuable remediation to limit the occurrence of these two drawbacks. In line with this, a series of fluorine-doped TiO2 samples (with F/O ratio varying in the 1–10 at.% range) were synthesized, in single step, by flame spray pyrolysis starting from organic solutions containing titanium tetra-isopropoxide (Ti(OC3H7)4) and hexafluorobenzene (C6F6) as titanium and fluorine precursors, respectively. By means of the selected synthesis technique, doping can be conveniently carried out by co-dissolving the dopant source, along with the TiO2 precursor, directly in the employed solvent (i.e., xylene), with a precise engineering of dopant concentration during synthesis. Quantitative crystalline phase analysis, performed by applying the Rietveld refinement method to XRPD data, highlighted the presence of both anatase and rutile phases in all the prepared samples, with the former being always predominant. Accordingly, all samples exhibited a UV-vis absorption edge at λ = ca. 400 nm. The prepared powders were then deposed on fluorine-doped tin oxide (FTO) glass by means of the doctor-blade technique, to investigate the effect of F-doping on the photoelectrochemical activity of TiO2. Incident Photon-to-Current Efficiency (IPCE), reflecting the semiconductor’s ability of generating and transferring photopromoted e-/h+ under irradiation and suitable applied voltage, was found to increase with increasing the F-dopant concentration, up to a F/O ratio of 5 at.%. This finding pointed to an improved separation of photopromoted electron-hole pairs, ascribed to the formation of intra-band gap states, induced by fluorine doping and able to efficiently trap photoproduced charge carriers. Conversely, when the amount of F-doping exceeded the optimum value, structural defects acting as e-/h+ recombination centers were formed, reasonably yielding lower photocurrent.

F-doped TiO2 prepared by flame spray pyrolysis: effect on the photoelectrochemical performance / G. Sinibaldi, F. Riboni, G.L. Chiarello, E. Selli. ((Intervento presentato al convegno Italian Photochemistry Meeting tenutosi a Besate nel 2014.

F-doped TiO2 prepared by flame spray pyrolysis: effect on the photoelectrochemical performance

F. Riboni
Secondo
;
G.L. Chiarello
Penultimo
;
E. Selli
Ultimo
2014

Abstract

Photoelectrochemical water splitting performed with semiconductor materials has attracted attention due to potential clean energy production, achievable utilizing light. In this context, TiO2 is the most investigated semiconductor, though characterized by i) low rate of photopromoted e- transfer and ii) high recombination rate of photoproduced charge carriers (e-/h+ pairs). Doping with non-metal elements is often suggested as a valuable remediation to limit the occurrence of these two drawbacks. In line with this, a series of fluorine-doped TiO2 samples (with F/O ratio varying in the 1–10 at.% range) were synthesized, in single step, by flame spray pyrolysis starting from organic solutions containing titanium tetra-isopropoxide (Ti(OC3H7)4) and hexafluorobenzene (C6F6) as titanium and fluorine precursors, respectively. By means of the selected synthesis technique, doping can be conveniently carried out by co-dissolving the dopant source, along with the TiO2 precursor, directly in the employed solvent (i.e., xylene), with a precise engineering of dopant concentration during synthesis. Quantitative crystalline phase analysis, performed by applying the Rietveld refinement method to XRPD data, highlighted the presence of both anatase and rutile phases in all the prepared samples, with the former being always predominant. Accordingly, all samples exhibited a UV-vis absorption edge at λ = ca. 400 nm. The prepared powders were then deposed on fluorine-doped tin oxide (FTO) glass by means of the doctor-blade technique, to investigate the effect of F-doping on the photoelectrochemical activity of TiO2. Incident Photon-to-Current Efficiency (IPCE), reflecting the semiconductor’s ability of generating and transferring photopromoted e-/h+ under irradiation and suitable applied voltage, was found to increase with increasing the F-dopant concentration, up to a F/O ratio of 5 at.%. This finding pointed to an improved separation of photopromoted electron-hole pairs, ascribed to the formation of intra-band gap states, induced by fluorine doping and able to efficiently trap photoproduced charge carriers. Conversely, when the amount of F-doping exceeded the optimum value, structural defects acting as e-/h+ recombination centers were formed, reasonably yielding lower photocurrent.
nov-2014
Settore CHIM/02 - Chimica Fisica
F-doped TiO2 prepared by flame spray pyrolysis: effect on the photoelectrochemical performance / G. Sinibaldi, F. Riboni, G.L. Chiarello, E. Selli. ((Intervento presentato al convegno Italian Photochemistry Meeting tenutosi a Besate nel 2014.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/278018
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