Sulfurization and Atmosphere Air Plasma Treatment of SnSx (x=1 2) Thin Films as an Effective Catalyst for Efficient Water Splitting

Abstract

Two-dimensional SnSx (x = 1 2) nanocrystals are attractive catalysts for photoelectrochemical water splitting as their components are earth-abundant and environmentally friendly SnS mixed-phase (orthorhombic and cubic phases) were synthesized by using a simple and facile colloidal method The tin precursor was synthesized using tin oxide (SnO) and oleic acid (OA) while the sulfur precursor was prepared using sulfur powder (S) and oleylamine (OLA) The sulfur precursor was injected into the tin precursor and the prepared SnS nanocrystals were precipitated at a final reaction temperature of 190oC In the first part of the study we have fabricated SnS thin-film photoelectrodes by spin coating mixed-phase SnS nanocrystals synthesized via a hot-injection technique on glass/Cr/Au substrates The obtained SnS thin films can be transformed into SnS2 by introducing structural phase changes via a facile low-vacuum annealing protocol in the presence of sulfur This sulfurization process enables the insertion of sulfur atoms between layers of SnS and results in the generation of shallow donors that alter the mechanism for water splitting The SnS2 thin films are used as stable photocatalysts to drive the oxygen evolution reaction and the light-current density of 0 233 mA/cm2 at 1 1V vs RHE can be achieved due to the high carrier density lower charge transfer resistance and a suitable reaction band position Based on a combination of UV-Vis spectroscopy (ultraviolet and visible spectroscopy) cyclic voltammetry and Mott–Schottky analysis the band positions and band gaps of SnS and SnS2 relative to the electrolyte are determined and a detailed mechanism for water splitting is presented Second we demonstrate enhanced water-splitting performance (I = 10 mA/cm2 Tafel slope = 60 mV/dec onset potential = -80 mV) of atmospheric air plasma treated (AAPT) SnS thin films through hydrogen evolution reaction (HER) The as-prepared SnS films are subjected to Atmospheric Air Plasma Treatment (AAPT) which leads to formation of additional phases of Sn and SnO2 at plasma powers of 150 W and 250 W respectively The AAPT treatment at 150 W leads to the evaporation of the S atoms as SO2 generating a number of S-vacancies and Sn active edge sites over the surface of the SnS thin film S-vacancies also create Sn active edge sites surface p-type pinning that tunes the suitable band positions and the hydrophilic surface which is beneficial for hydrogen adsorption/desorption At high plasma power (250 W) the surface of the SnS films get oxidized and degrade the HER performance Our results demonstrate the potential of the sulfurization and atmospheric air plasma treatment (150W) process is capable to improve the HER performance of SnS thin films as promising photocatalysts for efficient and large-scale water splitting

Date of Award	2019
Original language	English
Supervisor	Jow-Lay Huang (Supervisor)