Operando Characterization of an Amorphous Molybdenum Sulfide Nanoparticle Catalyst during the Hydrogen Evolution Reaction

Abstract

Molybdenum sulfide structures, particularly amorphous MoS 3 nanoparticles, are promising materials in the search for cost-effective and scalable watersplitting catalysts. Ex situ observations show that the nanoparticles exhibit a composition change from MoS 3 to defective MoS 2 when subjected to hydrogen evolution reaction (HER) conditions, raising questions regarding the active surface sites taking part in the reaction. We tracked the in situ transformation of amorphous MoS 3 nanoparticles under HER conditions through ambient pressure X-ray photoelectron spectroscopy and performed density functional theory studies of model MoS x systems. We demonstrate that, under operating conditions, surface sites are converted from MoS 3 to MoS 2 in a gradual manner and that the electrolytic current densities are proportional to the extent of the transformation. We also posit that it is the MoS 2 edge-like sites that are active during HER, with the high activity of the catalyst being attributed to the increase in surface MoS 2 edge-like sites after the reduction of MoS 3 sites.

In Situ Detection of Active Edge Sites in Single-Layer MoS2 Catalysts

“…where S2p BEs were found to be larger for the S atoms forming dimers than for monomeric edge S 21 . Another effect in our spectra is that the interaction with the Au support splits the basal plane S atoms into a higher BE component (for the bottom layer S atoms in contact with Au(111)) and a lower BE component (for the upper S layer).…”

Combining theory and experiment in electrocatalysis: Insights into materials design

“…in the fabrication of photoelectrochemical devices. The composition of the as-synthesized amorphous molybdenum sulfide materials was determined to be close to MoS 3 , but upon applying reducing potentials in an electrochemical cell, the surface transformed to MoS 2 as evidenced by in-situ studies (43,44). Amorphous molybdenum sulfides can be further doped with transition metals such as Fe, Co and Ni, improving their activity significantly (45).…”

Stability, Structure and Reconstruction of 1H‐Edges in MoS2

“…When reducing the lateral size of the 2D sheets to the nanoscale the properties of the edges become important and the relative stability of the different edges controls the morphology of small nanoclusters of MoS 2 . Edges play a crucial role in catalytic processes, such as the hydrodesulfurization reaction, the hydrogen evolution reaction, and the chemical functionalization of MoS 2 . They are also suggested to be important as anode catalysts in solid oxide fuel cells, and to have possible application as high power, fast charge/discharge cathodes for Li‐ion batteries, and spin‐filters .…”