Researchers Develop Nanosheets for Hydrogen Generation and Optoelectronic Applications

By Taha KhanSep 7 2022Reviewed by Laura Thomson

The use of solar energy is regarded as one of the most promising and significant technologies. This is because of its powerful capacity for water separation during the creation of clean fuel, H₂, and the decrease in CO₂ gas emissions and degradation of organic contaminations that contribute to environmental protection. Converting solar energy into electricity using a photoelectrochemical (PEC) photoelectrode is a practical approach.

Photoelectrochemical (PEC) Electrode

A high-performance PEC electrode must have an efficient electron‐hole pair separation, excellent carrier transportation, broad spectral response, low cost, high conversion, and strong light‐matter interaction. Enlarging the surface area and active sites significantly improves the morphology of the produced materials. Nanotubes, nanowires, and nanosheets are attractive materials for use in the energy sector. The bandgap increases due to the improvement in morphology, making it more suited for Vis-region light absorption.

Various photoanode materials and nanostructures have been researched to improve the efficacy of light absorption and capture by photoanodes. In PEC solar energy applications, semiconductor materials, including ZnO, transition metal dichalcogenides (TMDs, such as WSe₂, MoS₂), CuO and TiO₂ are given more significant consideration than Pt because of their cost-effectiveness, acceptable bandgap, wide spectrum response, and excellent chemical stability.

Transition Metal Dichalcogenides (TMDs)

TMDs are 2D layered materials with strong semiconducting qualities and flexible features. Light-matter interactions are effective in TMDs with a few nanometers of thickness. As a result, they have a higher absorption capacity (up to 5–10% of incoming sunlight) than popular solar absorbers such as GaAs and Si. Due to their great optical benefits, TMDs are essential materials with high performance and flexible optical absorbance.

Molybdenum Disulfide (MoS₂)

Molybdenum disulfide (MoS₂) is a potential material for several fields, including optoelectronics, electronics, and photonics, because of its excellent semiconducting characteristics and wide range of applications. Because of its thickness-modulated optical energy gap, MoS₂ possesses a comprehensive spectrum response in the region from UV to near IR, making it possible for it to be used in photovoltaics.

This study describes the fabrication of 2D MoS₂ nanosheet film utilized as the photoelectrode material for PEC hydrogen generation and optoelectronics by light sensing. The film is coated on PET/ITO substrate through a simple one-step electrophoretic deposition (EPD) technique.

2D MoS₂ Nanosheets Film Preparation

As the film's predecessor, 2D MoS₂ nanosheet suspensions were used. The EPD process is a quick, clean, and economical way to create a film on any conductive substrate's surface. Using a PET/ITO conductive substrate, a DC voltage of 7 V was applied between two electrodes in the presence of the homogenous MoS₂ mixed solution to deposit the film. It was then allowed to cure for five hours at 80 °C in a drying oven.

Characterization and Measurement

Raman spectroscopy and X-ray diffraction (XRD) were used to analyze the crystal structure, whereas a scanning electron microscope (SEM) and a transmission electron microscope were used to capture the micrograph. In addition, a spectrophotometer was used to measure the optical absorbance in the spectral region of 250 to 1100 nm.

PEC performance was assessed using a typical three-electrode setup and an electrochemical workstation. The produced films were employed as a photoelectrode material for PEC applications, where experiments on PET/ITO/MoS2 were carried out using a conventional three-electrode system in an electrolyte of 0.5 M Na₂SO₄ (pH = 7). In this three-electrode system, the prepared film, Pt, and Ag/AgCl were used as the working electrodes (photoanodes), the reference electrodes, and the counter electrodes. A 300 W xenon light was used to illuminate the area.

Significant Findings of the Study

In this study, by using an EPD technique, a lateral 2D MoS₂ nanosheet was created. High-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), and SEM validated the homogeneous morphology with a particle size of 60 nm, whereas XRD determined the synthesized 2D MoS2's chemical structure.

The optical spectra yielded a band gap value of 1.59 eV. A xenon lamp is utilized as the light source to generate hydrogen using the PET/ITO/MoS₂ electrode and 0.5 M Na2SO_4, and the J_ph values range from 0.4 to 0.98 mA.cm^-2 for darkness and light, respectively.

Photocurrent is calculated for V = 0 V, where J_ph is 0.44 mA.cm^-2. The electrode's strong responsiveness shows the photoelectrode's optoelectronic behavior to light. This low-cost technology makes it simple and inexpensive to create the prepared electrode.

Reference

Ahmed Adel A. Abdelazeez, Amira Ben Gouider Trabelsi , Fatemah. H. Alkallas, Samira Elaissi and Mohamed Rabia. (2022) Facile Preparation of Flexible Lateral 2D MoS2 Nanosheets for Photoelectrochemical Hydrogen Generation and Optoelectronic Applications. Photonics. https://www.mdpi.com/2304-6732/9/9/638

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