In this work, the growth of FeS 2 by direct sulfuration of Fe thin films is examined with the purpose of elucidating the nature of the Fe to FeS 2 transformation and to state some of its characteristics. To this aim, the film Seebeck coefficient (S) was measured during the whole sulfuration treatment. The S value changes from positive (ca. +8 μV K −1 ) to negative values (ca. −15 μV K −1 ) and, then, to very positive (ca. +100 μV K −1 ) at the end of the sulfuration process. To understand the film transformations and the resulting S evolution (mainly, the cause of its negative values) some Fe films were sulfurated during some selected times and, then, quickly cooled (to prevent changes in the chemical composition of the films) from the corresponding sulfuration temperature to room temperature (RT). Chemical composition and structural analyses of the quenched samples were accomplished at RT. Using the obtained data, it was concluded that the sulfuration transforms the original Fe film into hexagonal pyrrhotite (Fe 1−x S H ), which partially converts to its orthorhombic (Fe 1−x S O ) phase through a Neél transformation. Then, both the orthorhombic and hexagonal pyrrhotites react with sulfur to form pyrite (FeS 2 ). These chemical transformations are accompanied by changes of the film conductivity type: from p-type (Fe) to n-type (pyrrhotites) and finally to p-type (FeS 2 ). The intermediate pyrrhotite phases appear to be precursors of the final pyrite phase. Results are discussed in the light of former data on sulfurated thin films and Fe bulk samples.
N-Type
pyrite (FeS2) thin films, deposited on titanium
substrates, have been synthesized and photoelectrochemically characterized.
Its flat band potential has been estimated to be −0.75 ±
0.05V vs Ag/AgCl by electrochemical impedance spectroscopy (EIS).
The corresponding energy level diagram of the FeS2/electrolyte
interface has been established. Profuse hydrogen flows have been produced
under visible light illumination of FeS2 photoanode in
a photoelectrochemical cell (PEC) at different bias potentials. Their
values, measured by mass spectrometry (MS), were higher than 5 μmol
H2/min·cm2. Hydrogen photogeneration efficiencies
of ∼8% have been reached.
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