Nickel nanoparticle-activated MoS2 for efficient visible light photocatalytic hydrogen evolution

Activating two-dimensional semiconductors for photocatalysis: a cross-dimensional strategy

The emerging two-dimensional (2D) semiconductors substantially extend materials bases for versatile applications such as semiconductor photocatalysis demanding semiconductive matrices and large surface areas. The dimensionality, while endowing 2D semiconductors the unique properties to host photocatalytic functionality of pollutant removal and hydrogen evolution, hurdles the activation paths to form heterogenous photocatalysts where the photochemical processes are normally superior over these on the mono-compositional counterparts. In this perspective, we present a cross-dimensional strategy to employ thenD (n= 0-2) clusters or nanomaterials as activation partners to boost the photocatalytic activities of the 2D semiconductors. The formation principles of heterogenous photocatalysts are illustrated specifically for the 2D matrices, followed by selection criteria of them among the vast 2D database. The computer investigations are illustrated in the density functional theory route and machine learning benefitted from the vast samples in the 2D library. Synthetic realizations and characterizations of the 2D heterogenous systems are introduced with an emphasis on chemical methods and advanced techniques to understand materials and mechanistic studies. The perspective outlooks cross-dimensional activation strategies of the 2D materials for other applications such as CO2removal, and materials matrices in other dimensions which may inspire incoming research within these fields.

Doped MoS2 Polymorph for an Improved Hydrogen Evolution Reaction

Green hydrogen produced from solar energy could be one of the solutions to the growing energy shortage as non-renewable energy sources are phased out. However, the current catalyst materials used for photocatalytic water splitting (PWS) cannot compete with other renewable technologies when it comes to efficiency and production cost. Transition-metal dichalcogenides, such as molybdenum disulfides (MoS₂), have previously proven to have electronic and optical properties that could tackle these challenges. In this work, optical properties, the d-band center, and Gibbs free energy are calculated for seven MoS₂ polymorphs using first-principles calculations and density functional theory (DFT) to show that they could be suitable as photocatalysts for PWS. Out of the seven, the two polymorphs 3H_a and 2R₁ were shown to have d-band center values closest to the optimal value, while the Gibbs free energy for all seven polymorphs was within 5% of each other. In a previous study, we found that 3H_b had the highest electron mobility among all seven polymorphs and an optimal bandgap for photocatalytic reactions. The 3H_b polymorphs were therefore selected for further study. An in-depth analysis of the enhancement of the electronic properties and the Gibbs free energy through substitutional doping with Al, Co, N, and Ni was carried out. For the very first time, substitutional doping of MoS₂ was attempted. We found that replacing one Mo atom with Al, Co, I, N, and Ni lowered the Gibbs free energy by a factor of 10, which would increase the hydrogen evolution reaction of the catalyst. Our study further shows that 3H_b with one S atom replaced with Al, Co, I, N, or Ni is dynamically and mechanically stable, while for 3H_b, replacing one Mo atom with Al and Ni makes the structure stable. Based on the low Gibbs free energy, stability, and electronic bandgap 3H_b, MoS₂ doped with Al for one Mo atom emerges as a promising candidate for photocatalytic water splitting.

A High-Performance MoS2-Based Visible-Near-Infrared Photodetector from Gateless Photogating Effect Induced by Nickel Nanoparticles

Recent advancements in two-dimensional materials have shown huge potential for optoelectronic applications. It is challenging to achieve highly effective and sensitive broadband photodetection based on MoS₂ devices. Defect engineering, such as introducing vacancies, can narrow the bandgap and boost the separation of photogenerated carriers by defect states but leads to a slow response speed. Herein, we propose a nickel nanoparticle-induced gateless photogating effect with a unique energy band structure to enable the application of defect engineering and achieve high optoelectronic performance. The device based on Ni nanoparticle-decorated MoS₂ with S vacancies exhibited high responsivities of 106.21 and 1.38 A W^-1 and detectivities of 1.9 × 10¹² and 8.9 × 10⁹ Jones under 532 and 980 nm illumination (visible to near infrared), respectively, with highly accelerated response speed. This strategy provides new insight into optimizing defect engineering to design high-performance optoelectronic devices capable of broadband photodetection.

Theoretical prediction and shape-controlled synthesis of two-dimensional semiconductive Ni3TeO6

Current progress in two-dimensional (2D) materials explorations leads to constant specie enrichments of possible advanced materials down to two dimensions. The metal chalcogenide-based 2D materials are promising grounds where many adjacent territories are waiting to be explored. Here, a stable monolayer Ni3TeO6 (NTO) structure was computationally predicted and its stacked 2D nanosheets experimentally synthesized. Theoretical design undergoes featuring coordination of metalloid chalcogen, slicing the bulk structure, geometrical optimizations and stability study. The predicted layered NTO structure is realized in nanometer-thick nanosheets via a one-pot shape-controlled hydrothermal synthesis. Compared to the bulk, the 2D NTO own a lowered bandgap energy, more sensitive wavelength selectivity and an emerging photocatalytic hydrogen evolution ability under visible light. Beside a new 2D NTO with the optoelectrical and photocatalytic merits, its existing polar space group, structural specification, and design route are hoped to benefit 2D semiconductor innovations both in species enrichment and future applications.

High-performance ZnIn2S4/Ni(dmgH)2 for photocatalytic hydrogen evolution: Ion exchange construction, photocorrosion mitigation, and efficiency enhancement by photochromic effect

In this work, a novel photocatalyst of ZnIn₂S₄/Ni(dmgH)₂ was designed by a simple chemical precipitation method and used to enhance hydrogen evolution under visible light irradiation. Along with vigorous discharges of hydrogen bubbles, an optimal rate of 36.3 mmol/g/h was reached under UV-Vis light for hydrogen evolution, nearly 4.9 times of the one from pure ZnIn₂S₄. The heterojunction exhibits steady hydrogen evolution capability and owns a high apparent quantum efficiency (AQE) of 20.45% under the monochromatic light at 420 nm. By coupling ZnIn₂S₄ with Ni(dmgH)₂, an extraordinary photochromic phenomenon was detected and attributed to the active Ni-S component in situ formed between the nickel and sulfur composites under light irradiation. The emerging sulfide benefits light absorption of the system and separation of photogenerated electron and hole pairs. Besides providing a promising photocatalyst for visible light hydrogen production, the present work is hoped to inspire new trends of catalytic medium designs and investigations.