Enhancing Hydrogen Evolution Activity of Monolayer Molybdenum Disulfide via a Molecular Proton Mediator

Spatially Confined Microcells: A Path toward TMD Catalyst Design

With the ability to maximize the exposure of nearly all active sites to reactions, two-dimensional transition metal dichalcogenide (TMD) has become a fascinating new class of materials for electrocatalysis. Recently, electrochemical microcells have been developed, and their unique spatial-confined capability enables understanding of catalytic behaviors at a single material level, significantly promoting this field. This Review provides an overview of the recent progress in microcell-based TMD electrocatalyst studies. We first introduced the structural characteristics of TMD materials and discussed their site engineering strategies for electrocatalysis. Later, we comprehensively described two distinct types of microcells: the window-confined on-chip electrochemical microcell (OCEM) and the droplet-confined scanning electrochemical cell microscopy (SECCM). Their setups, working principles, and instrumentation were elucidated in detail, respectively. Furthermore, we summarized recent advances of OCEM and SECCM obtained in TMD catalysts, such as active site identification and imaging, site monitoring, modulation of charge injection and transport, and electrostatic field gating. Finally, we discussed the current challenges and provided personal perspectives on electrochemical microcell research.

ZnMo-MOF as anti-CO hydrogen electrocatalyst enhance microbial electrosynthesis for CO/CO2 conversion

Microbial electrosynthesis (MES) is an electrically driven technology that can be used for converting CO/CO2 into chemicals. The unique electronic and substrate properties of CO make it an important research target for MES. However, CO can poison the cathode and increase the overpotential of hydrogen evolution reaction (HER), thus reducing the electron transfer rate via H2. This work evaluated the effect of an anti-CO HER catalyst on the performance of MES for CO/CO2 conversion. ZnMo-metal-organic framework (MOF) materials with different calcination temperatures were synthesized. ZnMo-MOF-800 with Mo2C nanoparticles as active centers exhibited excellent resistance to CO toxicity. It also obtained the highest hydrogen evolution and enhanced electron transfer rate in CO atmosphere. MES with ZnMo-MOF-800 cathode and Clostridium ljungdahlii as biocatalyst obtained 0.31 g L-1 d-1 acetate yield, 0.1 g L-1 d-1 butyrate yield, and 0.09 g L-1 d-1 2,3-butanediol yield in CO/CO2, while Pt/C only get 0.076 g L-1 d-1 acetate yield, 0.05 g L-1 d-1 butyrate yield and 0.02 g L-1 d-1 2,3-butanediol yield. ZnMo-MOF-800 was conducive to biofilm formation, enabling it to better resist CO toxicity. This work provides new opportunities for constructing a highly efficient cathode with an anti-CO hydrogen evolution catalyst to enhance CO/CO2 conversion in MES.

Tunable-pH Environment Induced by Local Anchor Effect of High Lewis Basicity Conductive Polymers toward Glycerol Upgrading Assisted Hydrogen Evolution

Hybrid organic/inorganic composites with the organic phase tailored to modulate the local chemical environment at the transition metal-based catalyst surface arise as an enchanting category of catalysts for electrocatalysis. A fundamental understanding of how the conductive polymers of different Lewis basicities affect the reaction path is, however, still lacking to guide rational catalyst design. Herein, polyaniline (PANI), poly(3,4-ethylenedioxythiophene) (PEDOT), and poly(vinyl alcohol) (PVA) manifesting different Lewis basicities are compared for their regulatory roles on the hydrogen evolution reaction (HER) and glycerol electrooxidation (GOR) pathways regarding local proton coverage. Concerted efforts from in situ Raman and DFT theoretical calculations unveil that conductive polymer/V2O5 surface with tunable local pH regulated by Lewis acidity/basicity. As a result of the tailored chemical environment, the restructured V2O5/PANI/NF composite demonstrates a low overall potential of 1.55 V at the partial current density of 50 mA cm-2 for formate. The glycerol upgrading assisted hydrogen evolution device composed of V2O5/PANI/NF exhibits excellent electrochemical performance at a maximal Faraday efficiency of 82%, ranking among state of the art.

Validating the Use of Conductive Atomic Force Microscopy for Defect Quantification in 2D Materials

Defects significantly affect the electronic, chemical, mechanical, and optical properties of two-dimensional (2D) materials. Thus, it is critical to develop a method for convenient and reliable defect quantification. Scanning transmission electron microscopy (STEM) and scanning tunneling microscopy (STM) possess the required atomic resolution but have practical disadvantages. Here, we benchmark conductive atomic force microscopy (CAFM) by a direct comparison with STM in the characterization of transition metal dichalcogenides (TMDs). The results conclusively demonstrate that CAFM and STM image identical defects, giving results that are equivalent both qualitatively (defect appearance) and quantitatively (defect density). Further, we confirm that CAFM can achieve single-atom resolution, similar to that of STM, on both bulk and monolayer samples. The validation of CAFM as a facile and accurate tool for defect quantification provides a routine and reliable measurement that can complement other standard characterization techniques.

Toward Edge Engineering of Two-Dimensional Layered Transition-Metal Dichalcogenides by Chemical Vapor Deposition

The manipulation of edge configurations and structures in atomically-thin transition metal dichalcogenides (TMDs) for versatile functionalization has attracted intensive interest in recent years. The chemical vapor deposition (CVD) approach has shown promise for TMD edge engineering of atomic edge configurations (1H, 1T or 1T'-zigzag or armchair edges) as well as diverse edge morphologies (1D nanoribbons, 2D dendrites, 3D spirals, etc.). These edge-rich TMD layers offer versatile candidates for probing the physical and chemical properties and exploring potential applications in electronics, optoelectronics, catalysis, sensing, and quantum technologies. In this Review, we present an overview of the current state-of-the-art in the manipulation of TMD atomic edges and edge-rich structures using CVD. We highlight the vast range of distinct properties associated with these edge configurations and structures and provide insights into the opportunities afforded by such edge-functionalized crystals. The objective of this Review is to motivate further research and development efforts to use CVD as a scalable approach to harness the benefits of such crystal-edge engineering.

Waste-Derived Catalysts for Water Electrolysis: Circular Economy-Driven Sustainable Green Hydrogen Energy

The sustainable production of green hydrogen via water electrolysis necessitates cost-effective electrocatalysts. By following the circular economy principle, the utilization of waste-derived catalysts significantly promotes the sustainable development of green hydrogen energy. Currently, diverse waste-derived catalysts have exhibited excellent catalytic performance toward hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water electrolysis (OWE). Herein, we systematically examine recent achievements in waste-derived electrocatalysts for water electrolysis. The general principles of water electrolysis and design principles of efficient electrocatalysts are discussed, followed by the illustration of current strategies for transforming wastes into electrocatalysts. Then, applications of waste-derived catalysts (i.e., carbon-based catalysts, transitional metal-based catalysts, and carbon-based heterostructure catalysts) in HER, OER, and OWE are reviewed successively. An emphasis is put on correlating the catalysts' structure-performance relationship. Also, challenges and research directions in this booming field are finally highlighted. This review would provide useful insights into the design, synthesis, and applications of waste-derived electrocatalysts, and thus accelerate the development of the circular economy-driven green hydrogen energy scheme.

Polyaromatic cores for the exfoliation of popular 2D materials

Two-dimensional (2D) nanomaterials have attracted interest from the scientific community due to their unique properties. The production of these materials has been carried out by diverse methodologies, the liquid phase exfoliation being the most promising one due to its simplicity and potential scalability. The use of several stabilizers allows to obtain dispersions of these 2D nanomaterials in solvents with low boiling points. Herein we describe a general exfoliation method for different 2D materials employing a biphasic water/dichloromethane system and two different (poly)aromatic hydrocarbons (PAHs). This method allows us to obtain dispersions of the exfoliated 2D materials with high concentrations in the organic solvent. Due to the low boiling point of dichloromethane, and therefore its easy removal, the obtained dispersions can be employed as additives for different composites. We corroborate that the exfoliation efficiency is improved due to the π-π and van der Waals interactions between the PAHs and the layers of the 2D materials.

Reconciling the Volcano Trend with the Butler-Volmer Model for the Hydrogen Evolution Reaction

The volcano trend has been widely utilized to forecast new optimum catalysts in computational chemistry while the Butler-Volmer relationship is the norm to explain current-potential characteristics from cyclic voltammetry in analytical chemistry. Herein, we develop an electrochemical model for hydrogen evolution reaction exchange currents that reconciles device-level chemistry, atomic-level volcano trend, and the Butler-Volmer relation. We show that the model is a function of the easy-to-compute hydrogen adsorption energy invariably obtained from first-principles atomic simulations. In addition, the model reproduces with high fidelity the experimental exchange currents for elemental metal catalysts over 15 orders of magnitude and is consistent with the recently proposed analytical model based on a data-driven approach. Our findings based on fundamental electrochemistry principles are general and can be applied to other reactions including CO2 reduction, metal oxidation, and lithium (de)intercalation reactions.

Surface engineering strategies for MoS2 towards electrochemical hydrogen evolution

Water splitting driven by renewable energy sources is an environmentally friendly and sustainable way to produce hydrogen as an ideal energy source in the future. Electrocatalysts can promote the water splitting performance at the both ends. Therefore, the development of cost-effective, high-performance electrocatalysis is a key factor in promoting water decomposition and renewable energy conversion. Among candidates, layered molybdenum disulfide (MoS 2 ) is considered as a most promising electrocatalyst to replace Pt for hydrogen evolution reaction (HER). Surface atomic engineering and interface engineering can induce new physicochemical properties for MoS 2 to greatly enhance HER activity. In this report, we summarize the latest improvement strategies and research progress to improve the catalytic activity of MoS 2 -based material catalysts through the surface and interface atomic and molecular engineering, thus effectively improving HER process. In addition, some unsolved problems in the large-scale application of modified MoS 2 catalyst are also discussed.

Super-stable SnO2/MoS2 enhanced the electrocatalytic hydrogen evolution in acidic environments

We designed a superstable SnO2/MoS2 coupled nanosheet array on carbon cloth, which exhibited interface engineering of SnO2/MoS2 with fast electron transfer and proton adsorption boosting electrocatalytic hydrogen evolution in acidic environments.