The study on the active origin of electrocatalytic water splitting using Ni-MoS2 as example

Recent Strategies for Ni3S2-Based Electrocatalysts with Enhanced Hydrogen Evolution Performance: A Tutorial Review

Water electrolysis represents one of the most environmentally friendly methods for hydrogen production, while its overall efficiency is primarily governed by the electrocatalyst. Nickel sulfides, e.g., Ni3S2, are considered to be highly promising catalysts for the hydrogen evolution reaction (HER) due to their distinctive chemical structure. However, the practical application of Ni3S2-based electrocatalysts is hindered by unsatisfactory high overpotential in the HER and weakened catalytic performance under alkaline conditions. Therefore, in this regard, further research on Ni3S2-based catalysts is being carried out to tackle these challenges. This review provides a comprehensive survey of the latest advancements in Ni3S2-based in improving the HER performance of Ni3S2-based electrocatalysts. The review may offer some inspiration for the rational design and synthesis of novel transition metal-based catalysts with enhanced water electrolysis performance.

A customizable wireless potentiostat for assessing Ni(OH)2 decorated vertically aligned MoS2 thin films for electrochemical sensing of dopamine

In this study, we show that on-chip grown, vertically aligned MoS2 films that are decorated with Ni(OH)2 catalyst are suitable materials to be applied as working electrodes in electrochemical sensing. The constructed sensors display a highly repeatable response to dopamine, used as a model analyte, in a large dynamic range from 1 μM to 1 mM with a theoretical detection limit of 0.1 μM. In addition, to facilitate practical implementation of the sensor chips, we also demonstrate a low power wireless cyber-physical system that we designed and accommodated for cyclic voltammetry measurements. The developed cost-effective and portable instrument enables straightforward data acquisition, transfer and visualization through an Android mobile interface, and has an accuracy comparable to reference analysis of our sensors using a commercial table-top laboratory potentiostat.

2D Monolayer Catalysts: Towards Efficient Water Splitting and Green Hydrogen Production

A viable alternative to non-renewable hydrocarbon fuels is hydrogen gas, created using a safe, environmentally friendly process like water splitting. An important role in water-splitting applications is played by the development of two-dimensional (2D) layered transition metal chalcogenides (TMDCs), transition metal carbides (MXenes), graphene-derived 2D layered nanomaterials, phosphorene, and hexagonal boron nitride. Advanced synthesis methods and characterization instruments enabled an effective application for improved electrocatalytic water splitting and sustainable hydrogen production. Enhancing active sites, modifying the phase and electronic structure, adding conductive elements like transition metals, forming heterostructures, altering the defect state, etc., can improve the catalytic activity of 2D stacked hybrid monolayer nanomaterials. The majority of global research and development is focused on finding safer substitutes for petrochemical fuels, and this review summarizes recent advancements in the field of 2D monolayer nanomaterials in water splitting for industrial-scale green hydrogen production and fuel cell applications.

Electrocatalytic hydrogenation of indigo by NiMoS: energy saving and conversion improving

An NiMo alloy bonded with sulfur (NiMoS) exhibits enhanced surface affinity toward water and organic molecules, thereby enhancing electrocatalytic hydrogenation (ECH) reactions through synergistic effects. In industrial processes, indigo, an ancient dye employed in the denim industry, is typically chemically reduced using sodium dithionite. However, this process generates an excess of toxic sulfide, which heavily contaminates the environment. ECH is a sustainable alternative for indigo reduction due to its reduced reliance on chemicals and energy consumption. In this study, carbon-felt (CF)-supported NiMoS was synthesized in a two-step process. First, the NiMo alloy was electrodeposited onto the CF surface, followed by sulfidation in an oven at 600 °C. NiMoS exhibits a larger electrochemically active surface area and a smaller charge transfer resistance compared to pure Ni and NiMo. Furthermore, NiMoS demonstrates excellent thermodynamic and kinetic properties for water splitting in strong alkaline solutions (1.0 M KOH). Additionally, optimal reaction conditions for the ECH of indigo were explored. Under the conditions of a 1.0 M KOH hydroxide medium with 10% methanol (v/v), an indigo concentration of 5 g L-1, a reaction temperature of 70 °C, and a current density of 10 mA cm-2, NiMoS/CF achieved remarkable improvements in both conversion (99.2%) and Faraday efficiency (38.1%). The results of this experimental work offer valuable insights into the design and application of novel catalytic materials for the ECH of vat dyes, opening up new possibilities for sustainable and environmentally friendly processes in the dye industry.

Mechanism of the two-dimensional WSeTe/Zr2CO2 direct Z-scheme van der Waals heterojunction as a photocatalyst for water splitting

The direct Z-scheme van der Waals (vdW) heterojunctions based on biomimetic artificial photosynthesis are a promising strategy for enhancing photocatalytic activity. Therefore, the search for superior direct Z-scheme photocatalysts is an urgent task. Herein, we predicted the WSeTe/Zr₂CO₂ heterostructure as a potential direct Z-scheme photocatalyst based on density functional theory (DFT). The bands of the WSeTe/Zr₂CO₂ heterojunction follow a typical Type-II arrangement, where the interlayer band gap is smaller than that of the individual molecular layers, and staggered alignment of the large band-edge creates conditions that allow for a direct Z-scheme. The position of the Fermi energy levels of the two monolayers determines the formation of the built-in electric field pointing from WSeTe to Zr₂CO₂, promoting the desired interlayer electron-hole (e^--h⁺) recombination and suppressing the undesired carrier recombination. Finally, in-plane biaxial strain can effectively modulate the optoelectronic properties of the catalyst, while compressive strain has a more pronounced effect on the overpotential driving force of the material. Therefore, the WSeTe/Zr₂CO₂ heterojunction is an effective new photocatalyst satisfying the direct Z-scheme charge transfer mechanism with its specific application.

Recent advances in heterostructured cathodic electrocatalysts for non-aqueous Li-O2 batteries

Developing efficient energy storage and conversion applications is vital to address fossil energy depletion and global warming. Li-O2 batteries are one of the most promising devices because of their ultra-high energy density. To overcome their practical difficulties including low specific capacities, high overpotentials, limited rate capability and poor cycle stability, an intensive search for highly efficient electrocatalysts has been performed. Recently, it has been reported that heterostructured catalysts exhibit significantly enhanced activities toward the oxygen reduction reaction and oxygen evolution reaction, and their excellent performance is not only related to the catalyst materials themselves but also the special hetero-interfaces. Herein, an overview focused on the electrocatalytic functions of heterostructured catalysts for non-aqueous Li-O2 batteries is presented by summarizing recent research progress. Reduction mechanisms of Li-O2 batteries are first introduced, followed by a detailed discussion on the typical performance enhancement mechanisms of the heterostructured catalysts with different phases and heterointerfaces, and the various heterostructured catalysts applied in Li-O2 batteries are also intensively discussed. Finally, the existing problems and development perspectives on the heterostructure applications are presented.

Theoretical investigation on the hydrogen evolution reaction mechanism at MoS2 heterostructures: the essential role of the 1T/2H phase interface

DFT calculations have been performed to study the HER mechanism at 1T/2H MoS₂ heterostructures. The HER activity along the 1T/2H phase interface is comparable with those at the Mo-edge of 2H MoS₂ and the basal plane of 1T MoS₂.

Environmentally-Friendly Exfoliate and Active Site Self-Assembly: Thin 2D/2D Heterostructure Amorphous Nickel-Iron Alloy on 2D Materials for Efficient Oxygen Evolution Reaction

A class of 2D layered materials exhibits substantial potential for high-performance electrocatalysts due to high specific surface area, tunable electronic properties, and open 2D channels for fast ion transport. However, liquid-phase exfoliation always utilizes organic solvents that are harmful to the environment, and the active sites are limited to edge sites. Here, an environmentally friendly exfoliator in aqueous solution is presented without utilizing any toxic or hazardous substance and active site self-assembly on the inert base of 2D materials. Benefiting from thin 2D/2D heterostructure and strong interfacial coupling, the resultant highly disordered amorphous NiFe/2D materials (Ti3C2 MXene, graphene and MoS₂ ) thin nanosheets exhibit extraordinary electrocatalytic performance toward oxygen evolution reaction (OER) in alkaline media. DFT results further verify the experimental results. The study emphasizes a viable idea to probe efficient electrocatalysts by means of the synergistic effect of environmentally friendly exfoliator in aqueous solution and active site self-assembly on the inert base of 2D materials which forms the unique thin 2D/2D heterostructure in-suit. This new type of heterostructure opens up a novel avenue for the rational design of highly efficient 2D materials for electrocatalysis.

Datura-like Ni-HG-rGO as highly efficient electrocatalyst for hydrogen evolution reaction in alkaline conditions

Development of highly-active and noble-metal-free electrocatalysts for hydrogen evolution reactions is a challenge, and optimizing the structure and the composition of the relative materials is critical to obtain the high-quality catalysts. Ni-based compounds are being explored as noble-metal-free electrocatalysts in hydrogen evolution reactions but the Ni-based needs to be modified effectively. In this work, we co-electrodeposited Ni nanoparticles, hydrophilic graphene and graphene oxide layers on Ni foam to synthesize Ni-HG-rGO/NF catalysts. It was presented a Datura-like shape allowing for high performance with current densities of -10 and -100 mA cm^-2 for HER at overpotentials of -50 and -132 mV, a low Tafel slope of -48 mV dec^-1 and excellent long-term stability in 1.0 M NaOH solution. These results demonstrate that the Ni-HG-rGO/NF electrode can be a competitive electrode materials for HER in alkaline conditions.