Liquid-Phase Exfoliated GeSe Nanoflakes for Photoelectrochemical-Type Photodetectors and Photoelectrochemical Water Splitting

Abstract

Photoelectrochemical (PEC) systems represent powerful tools to convert electromagnetic radiation into chemical fuels and electricity. In this context, two-dimensional (2D) materials are attracting enormous interest as potential advanced photo(electro)catalysts and, recently, 2D group-IVA metal monochalcogenides have been theoretically predicted to be water splitting photocatalysts. In this work, we use density functional theory calculations to theoretically investigate the photocatalytic activity of single-/few-layer GeSe nanoflakes for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in pH conditions ranging from 0 to 14. Our simulations show that GeSe nanoflakes with different thickness can be mixed in the form of nanoporous films to act as nanoscale tandem systems, in which the flakes, depending on their thickness, can operate as HER-and/or OER photocatalysts. On the basis of theoretical predictions, we report the first experimental characterization of the photo(electro)catalytic activity of single-/few-layer GeSe flakes in different aqueous media, ranging from acidic to alkaline solutions: 0.5 M H 2 SO 4 (pH 0.3), 1 M KCl (pH 6.5), and 1 M KOH (pH 14). The films of the GeSe nanoflakes are fabricated by spray coating GeSe nanoflakes dispersion in 2-propanol obtained through liquid-phase exfoliation of synthesized orthorhombic (Pnma) GeSe bulk crystals. The PEC properties of the GeSe nanoflakes are used to design PEC-type photodetectors, reaching a responsivity of up to 0.32 AW −1 (external quantum efficiency of 86.3%) under 455 nm excitation wavelength in acidic electrolyte. The obtained performances are superior to those of several self-powered and low-voltage solution-processed photodetectors, approaching that of self-powered commercial UV−Vis photodetectors. The obtained results inspire the use of 2D GeSe in proof-of-concept water photoelectrolysis cells.

Two-Dimensional Gallium Sulfide Nanoflakes for UV-Selective Photoelectrochemical-type Photodetectors

“…Consequently, group-IIIA monochalcogenides can be engineered to fulfill the fundamental requirements for the water splitting photo(electro)catalysts, 13 , 21 , 27 i.e., (1) E CBM > reduction energy level of H + /H 2 ( E (H + /H 2 )) and (2) E VBM < reduction energy level of O 2 /H 2 O ( E (O 2 /H 2 O)). 64 − 66 Despite the existence of few experimental studies on the PEC properties of the most established monochalcogenides, such as InSe, 67 GaSe, 9 and GeSe, 13 no PEC characterizations have been reported for GaS, which is, therefore, a subject matter of interest for the realization of UV-harvesting components in photocatalytic tandem structures (e.g., van der Waals type-I heterojunctions). In this context, the double peak feature around the Γ-point in the so-called “Mexican-hat-like” ring-shaped valence band dispersion of single-/few (≤5)-layer GaS flakes effectively enhances the photoabsorption cross section.…”

Synthesis and Characterization of π-SnS Nanoparticles and Corresponding Thin Films

“…Chemically fabricated π-SnS thin film solar cell with the structure of stainless steel (SS)/π-SnS /CdS/ZnO/ZnO:Al/Ag showed η of 1.28% with a relatively higher V OC of 0.470 eV compared to the α-SnS based solar cell [10]. On the other hand, metal monochalcogenides (SiS, SiSe, SiTe, GeS, GeSe, GeTe, SnS, and SnSe) were theoretically predicted to be economical and eco-friendly hydrogen production photocatalysts [12][13][14]. The polymorph of tin sulfide, π-SnS exhibited interesting characteristics such as a high absorption coefficient of 10 −4 cm −1 in the visible region, a direct optical bandgap of 1.7 eV, and a p-type conducting nature with dark conductivity of about 10 −6 Ω −1 cm −1 [9], and had good photoconductivity response [10].…”

Hybrid Organic/Inorganic Photocathodes Based on WS2 Flakes as Hole Transporting Layer Material

“…However, the degradation was ascribed to the catalyst detachments, whereas no chemical analysis of CuI after the HER operation was reported. [ 55 ] More recently, 2D materials such as graphene oxide (GO), reduced graphene oxide (RGO), and transition metal dichalcogenides (TMDs) have been demonstrated as efficient CTLs and buffer layers in organic and perovskite solar cells, [ 75–82 ] as well as in other types of photoelectrodes, [ 83,84 ] including those for PEC cells. [ 70,71,85 ] In particular, GO‐ and RGO‐based HTLs and p‐doped MoS 2 have boosted the PEC performances of rr‐P3HT:PCBM photocathodes up to, respectively, J 0vsRHE = 6.01 mA cm −2 , V op = 0.6 V, [ 85 ] and J 0vsRHE = 1.21 mA cm −2 ; V op = 0.56 V. [ 71 ] Among 2D TMDs, WS 2 represents one of the most promising candidates for HTLs, thanks to high hole mobility ( ≈ 50 cm 2 V ‐1 s −1 ) and low effective hole reduced mass ( ≈ 0.46).…”