Bottom-Up Synthesized MoS2 Interfacing Polymer Carbon Nanodots with Electrocatalytic Activity for Hydrogen Evolution

Enhanced Microbial Protein Production from CO2 and Air by a MoS2 Catalyzed Bioelectrochemical System

Carbon dioxide can be relatively easily reduced to organic matter in a bioelectrochemical system (BES). However, due to insufficient reduction force from in-situ hydrogen evolution, it is difficult for nitrogen reduction. In this study, MoS2 was firstly used as an electrocatalyst for the simultaneous reduction of CO2 and N2 to produce microbial protein (MP) in a BES. Cell dry weight (CDW) could reach 0.81±0.04 g/L after 14 d operation at -0.7 V (vs. RHE), which was 108±3 % higher than that from non-catalyst control group (0.39±0.01 g/L). The produced protein had a better amino acid profile in the BES than that in a direct hydrogen system (DHS), particularly for proline (Pro). Besides, MoS2 promoted the growth of bacterial cell on an electrode and improved the biofilm extracellular electron transfer (EET) by microscopic observation and electrochemical characterization of MoS2 biocathode. The composition of the microbial community and the relative abundance of functional enzymes revealed that MoS2 as an electrocatalyst was beneficial for enriching Xanthobacter and enhancing CO2 and N2 reduction by electrical energy. These results demonstrated that an efficient strategy to improve MP production of BES is to use MoS2 as an electrocatalyst to shift amino acid profile and microbial community.

Facile and Scalable Colloidal Synthesis of Transition Metal Dichalcogenide Nanoparticles with High-Performance Hydrogen Production

Transition metal dichalcogenides (TMDs) have garnered significant attention as efficient electrocatalysts for the hydrogen evolution reaction (HER) due to their high activity, stability, and cost-effectiveness. However, the development of a convenient and economical approach for large-scale HER applications remains a persistent challenge. In this study, we present the successful synthesis of TMD nanoparticles (including MoS2, RuS2, ReS2, MoSe2, RuSe2, and ReSe2) using a general colloidal method at room temperature. Notably, the ReSe2 nanoparticles synthesized in this study exhibit superior HER performance compared with previously reported nanostructured TMDs. Importantly, the synthesis of these TMD nanoparticles can readily be scaled up to gram quantities while preserving their exceptional HER performance. These findings highlight the potential of colloidal synthesis as a versatile and scalable approach for producing TMD nanomaterials with outstanding electrocatalytic properties for water splitting.

Carbon Dots Strongly Immobilized onto Carbon Nanohorns as Non-Metal Heterostructure with High Electrocatalytic Activity towards Protons Reduction in Hydrogen Evolution Reaction

Highly performing, non-metal inexpensive electrocatalysts for the production of hydrogen via electrochemical water splitting are called for the replacement of current platinum-based ones. In order to speed up the electrocatalytic hydrogen evolution, abundant active sites but also efficient charge transfer is needed. In this context, 0D carbon dots (CDs) with large specific surface area, low cost, high conductivity, and rich functional groups emerge as promising non-metal electrocatalysts. Additionally, the use of conductive substrates provides an effective strategy to boost their electrocatalytic performance. Herein, the unique 3D superstructure of carbon nanohorns (CNHs), as well as without any metal content in their structure, is used to provide a conductive support of high porosity, large specific surface area, and good electrical conductivity, for the in situ growth and immobilization of CDs, via a simple hydrothermal method. The direct contact of CDs with the 3D conductive network of CNHs promotes charge transfer, accelerating hydrogen evolution. The all-carbon non-metal CDs/CNHs nanoensembleshows an onset potential close to the one of Pt/C, low charge transfer resistance, and excellent stability.

Synthesis and Characterization of Transition Metal Dichalcogenide Nanoribbons Based on a Controllable O2 Etching

Although the synthesis of monolayer transition metal dichalcogenides has been established in the last decade, synthesizing nanoribbons remains challenging. In this study, we have developed a straightforward method to obtain nanoribbons with controllable widths (25-8000 nm) and lengths (1-50 μm) by O₂ etching of the metallic phase in metallic/semiconducting in-plane heterostructures of monolayer MoS₂. We also successfully applied this process for synthesizing WS₂, MoSe₂, and WSe₂ nanoribbons. Furthermore, field-effect transistors of the nanoribbons show an on/off ratio of larger than 1000, photoresponses of 1000%, and time responses of 5 s. The nanoribbons were compared with monolayer MoS₂, highlighting a substantial difference in the photoluminescence emission and photoresponses. Additionally, the nanoribbons were used as a template to build one-dimensional (1D)-1D or 1D-2D heterostructures with various transition metal dichalcogenides. The process developed in this study offers simple production of nanoribbons with applications in several fields of nanotechnology and chemistry.

Molybdenum Diselenide and Tungsten Diselenide Interfacing Cobalt-Porphyrin for Electrocatalytic Hydrogen Evolution in Alkaline and Acidic Media

Easy and effective modification approaches for transition metal dichalcogenides are highly desired in order to make them active toward electrocatalysis. In this manner, we report functionalized molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2) via metal-ligand coordination with pyridine rings for the subsequent covalent grafting of a cobalt-porphyrin. The new hybrid materials were tested towards an electrocatalytic hydrogen evolution reaction in both acidic and alkaline media and showed enhanced activity compared to intact MoSe2 and WSe2. Hybrids exhibited lower overpotential, easier reaction kinetics, higher conductivity, and excellent stability after 10,000 ongoing cycles in acidic and alkaline electrolytes compared to MoSe2 and WSe2. Markedly, MoSe2-based hybrid material showed the best performance and marked a significantly low onset potential of -0.17 V vs RHE for acidic hydrogen evolution reaction. All in all, the ease and fast modification route provides a versatile functionalization procedure, extendable to other transition metal dichalcogenides, and can open new pathways for the realization of functional nanomaterials suitable in electrocatalysis.

Facile Synthesis of MoP-RuP2 with Abundant Interfaces to Boost Hydrogen Evolution Reactions in Alkaline Media

Exploiting efficient electrocatalysts for hydrogen evolution reactions (HERs) is important for boosting the large-scale applications of hydrogen energy. Herein, MoP-RuP₂ encapsulated in N,P-codoped carbon (MoP-RuP₂@NPC) with abundant interfaces were prepared via a facile avenue with the low-toxic melamine phosphate as the phosphorous resource. Moreover, the obtained electrocatalyst possessed a porous nanostructure, had abundant exposed active sites and improved the mass transport during the electrocatalytic process. Due to the above merits, the prepared MoP-RuP₂@NPC delivered a greater electrocatalytic performance for HERs (50 mV@10 mA cm⁻²) relative to RuP₂@NPC (120 mV) and MoP@NPC (195 mV) in 1 M KOH. Moreover, an ultralow potential of 1.6 V was required to deliver a current density of 10 mA cm⁻² in the two-electrode configuration for overall water splitting. For practical applications, intermittent solar energy, wind energy and thermal energy were utilized to drive the electrolyzer to generate hydrogen gas. This work provides a novel and facile strategy for designing highly efficient and stable nanomaterials toward hydrogen production.

Sulfur-Doped Carbon Nanohorn Bifunctional Electrocatalyst for Water Splitting

Sulfur-doped carbon nanohorns (S-CNHs) were prepared by an easy one-pot solvothermal process and were employed as efficient electrocatalysts towards water splitting. Initially, oxidation of CNHs followed by thermal treatment with the Lawesson's reagent resulted in the formation of S-CNHs with the sulfur content determined as high as 3%. The S-CNHs were thoroughly characterized by spectroscopic, thermal and electron microscopy imaging means and then electrocatalytically screened. Specifically, S-CNHs showed excellent activity and durability for both O2 and H2 evolution reactions, by showing low overpotential at 1.63 and -0.2 V vs. RHE for oxygen and hydrogen evolution reaction, respectively. Additionally, S-CNHs showed significantly lower Tafel slope value and lower current resistance compared to oxidized and pristine CNHs for both electrocatalytic reactions. The outstanding electrocatalytic properties and high conductivity, along with the high S-doping level, render S-CNHs a promising bifunctional electrocatalyst for water splitting.

Defect Engineering of Molybdenum-Based Materials for Electrocatalysis

Molybdenum-based electrocatalysts have been widely applied in electrochemical energy conversion reactions. The essential roles of defects, including doping, vacancies, grain boundaries, and dislocations in improving various electrocatalytic performances have been reported. This review describes the latest development of defect engineering in molybdenum-based materials for hydrogen evolution, oxygen reduction, oxygen evolution, and nitrogen reduction reactions. The types of defects, preparation methods, characterization techniques, and applications of molybdenum-based defect materials are elucidated. Finally, challenges and future research directions for these types of materials are also discussed.

Stabilization of metallic phases through formation of metallic/semiconducting lateral heterostructures

In this study, we develop a new approach for stabilization of metallic phases of monolayer MoS₂ through the formation of lateral heterostructures composed of semiconducting/metallic MoS₂. The structure of metallic (a mixture of T and T') and semiconducting (2H) phases was unambiguously characterized by Raman spectroscopy, x-ray photoelectron spectroscopy, photoluminescence imaging, and transmission electron microscope observations. The amount of NaCl, reaction temperature, reaction time, and locations of substrates are essential for controlling the percentage of metallic/semiconducting phases in lateral heterostructures; loading a large amount of NaCl at low temperatures with short reaction times prefers metallic phases. The existence of the semiconducting phase in MoS₂ lateral heterostructures significantly enhances the stability of the metallic phases through passivation of reactive edges. The same approach can be applied to other transition metal dichalcogenides (TMDs), such as WS₂, leading to boosting of basic research and application of TMDs in metallic phases.

Carbon Nanohorn-Based Electrocatalysts for Energy Conversion

In the context of even more growing energy demands, the investigation of alternative environmentally friendly solutions, like fuel cells, is essential. Given their outstanding properties, carbon nanohorns (CNHs) have come forth as promising electrocatalysts within the nanocarbon family. Carbon nanohorns are conical nanostructures made of sp2 carbon sheets that form aggregated superstructures during their synthesis. They require no metal catalyst during their preparation and they are inexpensively produced in industrial quantities, affording a favorable candidate for electrocatalytic reactions. The aim of this article is to provide a comprehensive overview regarding CNHs in the field of electrocatalysis and especially, in oxygen reduction, methanol oxidation, and hydrogen evolution, as well as oxygen evolution from water splitting, underlining the progress made so far, and pointing out the areas where significant improvement can be achieved.