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The ability to intercalate guest species into the van der Waals gap of 2D layered materials affords the opportunity to engineer the electronic structures for a variety of applications. Here we demonstrate the continuous tuning of layer vertically aligned MoS 2 nanofilms through electrochemical intercalation of Li + ions. By scanning the Li intercalation potential from high to low, we have gained control of multiple important material properties in a continuous manner, including tuning the oxidation state of Mo, the transition of semiconducting 2H to metallic 1T phase, and expanding the van der Waals gap until exfoliation. Using such nanofilms after different degree of Li intercalation, we show the significant improvement of the hydrogen evolution reaction activity. A strong correlation between such tunable material properties and hydrogen evolution reaction activity is established. This work provides an intriguing and effective approach on tuning electronic structures for optimizing the catalytic activity.2D materials | layer vertically standing | electrochemical catalysis L ayer-structured 2D materials are an interesting family of materials with strong covalent bonding within molecular layers and weak van der Waals interaction between layers. Beyond intensively studied graphene-related materials (1-4), there has been recent strong interest in other layered materials whose vertical thickness can be thinned down to less than few nanometers and horizontal width can also be reduced to nanoscale (5-9). The strong interest is driven by their interesting physical and chemical properties (2, 10) and their potential applications in transistors, batteries, topological insulators, thermoelectrics, artificial photosynthesis, and catalysis (4,(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25).One of the unique properties of 2D layered materials is their ability to intercalate guest species into their van der Waals gaps, opening up the opportunities to tune the properties of materials. For example, the spacing between the 2D layers could be increased by intercalation such as lithium (Li) intercalated graphite or molybdenum disulfide (MoS 2 ) and copper intercalated bismuth selenide (26-29). The electronic structures of the host lattice, such as the charge density, anisotropic transport, oxidation state, and phase transition, may also be changed by different species intercalation (26,27).As one of the most interesting layered materials, MoS 2 has been extensively studied in a variety of areas such as electrocatalysis (20)(21)(22)(30)(31)(32)(33)(34)(35)(36). It is known that there is a strong correlation between the electronic structure and catalytic activity of the catalysts (20,(37)(38)(39)(40)(41). It is intriguing to continuously tune the morphology and electronic structure of MoS 2 and explore the effects on MoS 2 hydrogen evolution reaction (HER) activity. Very recent studies demonstrated that the monolayered MoS 2 and WS 2 nanosheets with 1T metallic phase synthesized by chemical exfoliation exhibited superio...

Development of a non-noble-metal hydrogen-producing catalyst is essential to the development of solar water-splitting devices. Improving both the activity and the stability of the catalyst remains a key challenge. In this Communication, we describe a two-step reaction for preparing three-dimensional electrodes composed of CoSe2 nanoparticles grown on carbon fiber paper. The electrode exhibits excellent catalytic activity for a hydrogen evolution reaction in an acidic electrolyte (100 mA/cm(2) at an overpotential of ∼180 mV). Stability tests though long-term potential cycles and extended electrolysis confirm the exceptional durability of the catalyst. This development offers an attractive catalyst material for large-scale water-splitting technology.

Fabricating active materials into specific macrostructures is critical in the pursuit of high electro-catalytic activity. Herein we demonstrate that a three-dimensional (3D) architecture of NiFe layered double hydroxide (NiFe-LDH) significantly reduced the onset potential, yielded high current density at small overpotentials, and showed outstanding stability in electrochemical oxygen evolution reaction.