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

Abstract

The efficient production of molecular hydrogen (H2) is a fundamental step toward an environmentally friendly economy. Photocathodes using organic bulk heterojunction (BHJ) films as light harvesters represent an attracting technology for low‐cost photoelectrochemical water splitting. These photocathodes need charge transporting layers (CTLs) to efficiently separate and transport either holes or electrons toward the back‐current collector and electrolyte, respectively. Therefore, it is pivotal to control the energy band edge levels and the work function (WF) of the CTLs to match the ones of the BHJ film, current collector, and electrolyte. Herein, the use of 2D p‐doped WS2 flakes as hole transporting material for H2‐evolving photocathodes based on the regioregular poly(3‐hexylthiophene):phenyl‐C61‐butyric acid methyl ester (rr‐P3HT:PCBM) BHJ film is proposed. The WS2 flakes are produced through scalable liquid‐phase exfoliation of the bulk crystal, whereas p‐type chemical doping allows the tuning of the WS2 WF. This approach boosts the performances of the photocathodes, reaching photocurrent densities up to 4.14 mA cm−2 at 0 V versus reversible hydrogen electrode (RHE), an onset potential of 0.66 V versus RHE, and a ratiometric power‐saved metric of 1.28% (under 1 sun illumination). To the best of the authors' knowledge, these performances represent the current record for 2D materials‐based CTLs.

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

“…GaS single-/few-layer flakes were produced through ultrasonication-assisted LPE of bulk β-polytype in eco-friendly anhydrous 2-propanol (IPA) (see SI, Methods section) . The use of IPA as the exfoliating solvent circumvents the processability drawbacks related to the use of high-boiling-point and toxic solvents often used for the exfoliation of layered materials, − e.g., N -methyl-2-pyrrolidone (NMP) for graphene , and several metal chalcogenides Figure a shows a photograph of a representative GaS crystal, together with the top- and side-views of its hexagonal double-layered structure with the Ga–Ga and Ga–S distances of 2.48 and 2.37 Å, respectively, , and an interlayer distance approximating the monolayer thickness of ∼0.75 nm…”

Recent research progress on operational stability of metal oxide/sulfide photoanodes in photoelectrochemical cells

“…Compared with metal oxides whose VB is composed of the 2p orbital of O, the VB of metal sulfides is more negative, which enables them to exhibit a narrower Eg and thus utilize wider sunlight. Most metal sulfides have suitable forbidden bandwidths, energy band positions, and morphologies and unique quantum confinement effects; therefore, applying metal sulfide materials in the field of photocatalysis has been extensively discussed [13,154].…”

Topochemical Transformation of Two-Dimensional VSe2 into Metallic Nonlayered VO2 for Water Splitting Reactions in Acidic and Alkaline Media

“…Even more, the recombination reaction of the two surface hydroxyl groups V–OH may form water, restoring catalytic sites for the water dissociation . Such effects are promising to be exploited for the OER in both acidic and alkaline media, as well as for the HER in alkaline media. , Motivated by the above discussion, herein, VO 2 (R) nanosheets were synthesized through a topochemical conversion process of two-dimensional (2D) VSe 2 nanosheets, the latter produced by liquid-phase exfoliation (LPE) , of synthesized bulk crystals. During the topochemical synthesis of VO 2 (R) nanosheets, the selenium of VSe 2 is substituted by oxygen once the sample is annealed at 500 °C in a reductive H 2 /Ar atmosphere and subsequently exposed to ambient temperature.…”