Photoelectrochemical Study of Pyrargyrite in Acid Media

Abstract

Silver antimony sulfide (Ag 3 SbS 3 , pyrargyrite) was synthesized by a solid state route from silver, antimony and sulfur powder precursors under an argon atmosphere. The product was characterized by powder X-ray diffraction (XRD) and found to be Ag 3 SbS 3 pyrargyrite alone, with a bandgap (E g ) of 2.0 eV. We analyzed the ground sample by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The bulk composition was found to be consistent with stoichiometric ratios. Surface characterization by X-ray photoelectron spectroscopy (XPS) indicates that the surface is depleted of Ag and S with an excess of Sb. Surface oxygen was found to be predominantly bound to Sb. The electrochemical and photoelectrochemical behavior of films on fluorine-doped tin oxide was compared to the behavior of bulk electrodes prepared from pieces of pyrargyrite grown under Ar. The films' photoelectrochemical behavior was consistent with a p-type material with the conduction band aligned to reduce H + in acid media. The photocurrent showed evidence of states with energies in the forbidden region that were localized at the surface and filled in the dark. Under illumination, photogenerated holes oxidized these surface states and caused recombination. On platinized films, electrons from H 2 oxidation filled these states. Materials with photocatalytic activity in the visible region of solar spectra are of fundamental and practical interest. In applications for solar energy conversion such as water splitting, there is a need for stable materials that can perform electrochemical reactions.1 Since the first report on water splitting with TiO 2 , 2 the development of materials with lower bandgap, E g , than the ca. 3 eV of TiO 2 (e.g., for anatase E g = 3.2 eV) 3,4 has remained a challenge. Although significant progress has been made (e.g., Refs. 5-7) this remains a challenge because as well as E g , the valence band (VB) and conduction band (CB) must be aligned to enable the reaction of interest while the material must be stable. 8 In this paper, we present the preparation of phase-pure pyrargyrite, a material reported 9-11 to be p-type with E g = 2.0 eV. We propose that this material is of interest for water splitting because the conduction band is aligned for H + reduction to H 2 . Pyrargyrite is a naturally occurring silver ore. Its crystal structure has been studied from mined samples;12 natural crystals present high conductivity due to Ag ion mobility 13 with relatively low activation energy (ca. 0.5 eV). 12,13 This is one example of simple Ag-containing sulfosalts 12 that have received increasing attention because of their ionic conductive properties. 14 Pyrargyrite synthesized by a solid state route and its solid solutions of intermediate compositions covering Ag 2 S, Sb 2 S 3 and Ag 3 SbS 3 were studied electrochemically in aqueous cyanide solutions in the context of Ag extraction from Ag 3 SbS 3 and Ag 3 AsS 3 . 10In acid media, we are aware of two preliminary reports of pyrargyrite: one for mined powder in 2...

Ag3SbS3Liquid-Junction Semiconductor-Sensitized Solar Cells

“…24,25 It has wide applications in nonlinear optics and photocatalysts. 24,26 To our best knowledge, there has been no reports on the application of Ag 3 SbS 3 as a solar absorber material (preliminary photoelectrochemical study of Ag 3 SbS 3 has been explored, but no photovoltaic data were reported 27 ). Ag 3 SbS 3 nanoparticles, thin films and nanorods have been synthesized by hydrothermal, soft-chemical, polyol-mediated, chemical deposition and biomolecule-assisted methods.…”

“…24,25 It has wide applications in nonlinear optics and photocatalysts. 24,26 To our best knowledge, there has been no reports on the application of Ag 3 SbS 3 as a solar absorber material (preliminary photoelectrochemical study of Ag 3 SbS 3 has been explored, but no photovoltaic data were reported 27 ).…”