Two-dimensional silicon chalcogenides with high carrier mobility for photocatalytic water splitting

Abstract

Highly-efficient water splitting based on solar energy is one of the most attractive research focuses in the energy field. Searching for more candidate photocatalysts that can work under visible-light irradiation are highly demanded. Herein, using first principle calculations based on density functional theory (DFT), we predict that the two dimensional silicon chalcogenides, i.e. SiX (X=S, Se, Te) monolayers, as semiconductors with 2.43 eV~3.00 eV band gaps, exhibit favorable band edge positions for photocatalytic water splitting. The optical adsorption spectra demonstrate that the SiX monolayers have pronounced optical absorption in the visible light region. Moreover, the band gaps and band 2 edge positions of silicon chalcogenides monolayers can be tuned by applying biaxial strain or increasing the number of layers, in order to better fit the redox potentials of water. The combined novel electronic, high carrier mobility, and optical properties render the two dimensional SiX a promising photocatalyst for water splitting.Recently, a variety of two dimensional (2D) materials have been extensively studied as the photocatalysts for water splitting, due to their large specific surface areas as well as the short charge migration distances, which could enhance the catalytic performance by hindering the electronhole recombination. 10-15 A typical example is monolayer SnS 2 , which 3 yielded a photocurrent density of 2.75 mA cm -2 at 1.0 V, nearly 72 times larger than that of bulk SnS 2 , proven in theory and experiment. 9 Other 2D materials such as transition metal dichalcogenides, 16 MXenes, 17 group-III monochalcogenides, 18 ternary zinc nitrides, 19,20 and MPSe 3 21 etc. have also been predicated theoretically for photocatalyst application.Moreover, the booming research advancements of the stabilities and electronic properties of group IV-VI monolayers, which are isoelectronic counterparts of group V such as phosphorene, have been reported in the last few years. [22][23][24][25][26][27][28][29][30][31][32] The group IV mono-chalcogenides MX (M= Si, Ge, Sn and X = S or Se), whose buckled honeycomb lattice is similar to that of black phosphorene, are also candidate materials for photocatalytic water splitting. Nevertheless, their calculated overpotentials for OER are quite large, or a specific basic or acidic condition is required to obtain good photocatalytic activity. 33 The monolayer germanium monochalcogenides, like blue phosphorene, was predicted as UV-light-driven photocatalyst, owing to the large band gap. 34 Therefore, it is highly worthwhile to further investigate the electronic and optical properties of other group IV-VI monolayers, for the sake of finding new candidate materials with improved properties for optoelectronic devices. Motivated by this conception, we have conducted a comprehensive investigation of the stability and electronic properties of silicon chalcogenides, i.e. SiX (X=S, Se and Te) monolayers, based on density 4 functional theory. It is found that the SiX monolayers are of high dynamic, m...

Prediction of hydrogenated group IV–V hexagonal binary monolayers

“…10 . A semiconductor could be a potential photocatalyst for water splitting if the CBM energy is higher than the reduction potential of , and the VBM energy is lower than the oxidation potential of 72 . It should be noted that there are not many photocatalysts that meet all of the requirements, so far.…”

Bonding, structure, and mechanical stability of 2D materials: the predictive power of the periodic table

“…225 The structural data of group IV-VI monolayers MX, with M = C, Si, Ge, Sn and X = S, Se, Te, has been determined in a comprehensive study by first-principles calculations. 225 Table 10 contains the cohesive energies and structural data of CS, 225 SiS, [225][226][227] GeS, 224,225,228 SnS, 224,225,229 CSe, 225,226,230,231 SiSe, [225][226][227] GeSe, 224,225,232 SnSe, 224,225,232 CTe, 225,226 SiTe, 225,233 GeTe, 225,226,234 and SnTe. 225,234 In a plot of cohesive energies versus the bond lengths of IV-VI monolayers, we group together chemically related compounds, obtained by combining one group IV element with all other group VI elements (see Fig.…”

“…The available linear and nonlinear mechanical properties studied for the compounds CSe, 231 SiS, 227 SiSe, 227 SiTe, 227,233 GeS, 14,[234][235][236] GeSe, 14,[234][235][236] GeTe, 234 SnS, 14,[234][235][236] SnSe, 14,[234][235][236] and SnTe 234 are summarized in Table 11. The plot of Young's modulus and strength versus bond length in Fig.…”

Reconsidering X-ray Photoelectron Spectroscopy Quantification of Substitution Levels of Monolayers on Unoxidized Silicon Surfaces

“…Within the continuum model as shown in Figure 5, the total Si 2p signal intensity at the alkyl chain-modified surface is given by 14If we assume , and , Eq 14 can be written as (15) Substituting Eq 10, , Eq 15 becomes (16) The carbon signal from the alkyl group is given by (17) where the same assumptions and substitutions are made when deriving Eq 16. The signal from the fluorine layer is given by (18) We can assume that , Eq 18 becomes Given that , the signal from the fluorine layer is given by (19) The intensity of adventitious carbon signal is given by (20) Combining Eq 17 and 20, the total intensity of the carbon signal is given by (21) After obtaining the intensity of the silicon signal, ISi (Eq 16), the intensity of fluorine signal, IF (Eq 19), and the total intensity of carbon signal, IC total (Eq 21), two quantification methods for the substitution level, using the ratio of C to Si, IC total /ISi, or the ratio of F to Si, IF/ISi, respectively, will be derived as shown below.…”