Contributions of Phase, Sulfur Vacancies, and Edges to the Hydrogen Evolution Reaction Catalytic Activity of Porous Molybdenum Disulfide Nanosheets

Abstract

Molybdenum disulfide (MoS2) is a promising nonprecious catalyst for the hydrogen evolution reaction (HER) that has been extensively studied due to its excellent performance, but the lack of understanding of the factors that impact its catalytic activity hinders further design and enhancement of MoS2-based electrocatalysts. Here, by using novel porous (holey) metallic 1T phase MoS2 nanosheets synthesized by a liquid-ammonia-assisted lithiation route, we systematically investigated the contributions of crystal structure (phase), edges, and sulfur vacancies (S-vacancies) to the catalytic activity toward HER from five representative MoS2 nanosheet samples, including 2H and 1T phase, porous 2H and 1T phase, and sulfur-compensated porous 2H phase. Superior HER catalytic activity was achieved in the porous 1T phase MoS2 nanosheets that have even more edges and S-vacancies than conventional 1T phase MoS2. A comparative study revealed that the phase serves as the key role in determining the HER performance, as 1T phase MoS2 always outperforms the corresponding 2H phase MoS2 samples, and that both edges and S-vacancies also contribute significantly to the catalytic activity in porous MoS2 samples. Then, using combined defect characterization techniques of electron spin resonance spectroscopy and positron annihilation lifetime spectroscopy to quantify the S-vacancies, the contributions of each factor were individually elucidated. This study presents new insights and opens up new avenues for designing electrocatalysts based on MoS2 or other layered materials with enhanced HER performance.

Cobalt-Doped Iron Sulfide as an Electrocatalyst for Hydrogen Evolution

“…[11][12][13][14] Among these materials, two-dimensional layered MoS 2 received great attention. Moreover, MoS 2 is the first earth abundant compound to be studied as an HER catalyst, and its catalytic activity has been significantly boosted over the last decade, [15][16][17] but beyond the scope of the present investigation.…”

Modifying Commercial Carbon with Trace Amounts of ZIF to Prepare Derivatives with Superior ORR Activities

“…Metal oxide nanoparticles, metal-N 4 complexes, metal-C-N moieties, and defects of the carbon substrates could all independently function as active centers, but it is unknown which of these centers is best for ORR. The methods to enhance electrochemical activities mainly rely on four aspects: (1) increasing the intrinsic activities of active centers, [23][24][25] (2) augmenting the amount or concentration of active centers, [25][26][27] (3) optimizing mass transfer during the reaction, [28,29] (4) enhancing the conductivity of catalysts. [10][11][12][13][14] Such catalysts should be further explored to fulfill the requirements of cell optimizations and applications.…”

“…[20] However, graphene and carbon nanotubes are not cheap, which have impeded practical applications. The methods to enhance electrochemical activities mainly rely on four aspects: (1) increasing the intrinsic activities of active centers, [23][24][25] (2) augmenting the amount or concentration of active centers, [25][26][27] (3) optimizing mass transfer during the reaction, [28,29] (4) enhancing the conductivity of catalysts. Vulcan XC72 conductive carbon black (VXC72) is one of the most widely used carbon materials in fuel cells due to its good dispersibility, large surface area, and high conductivity.…”

Hydrogen evolution activity of individual mono-, bi-, and few-layer MoS 2 towards photocatalysis

“…We note that both the edge sites of MoS 2 and the sulfur vacancies at the inert basal plane play an important role for the HER [66]. We assume a constant density of sulfur vacancies of SA −1 = (1.0 ± 0.5) · 10 13 cm −2 for our exfoliated MoS 2 flakes [67].…”