Structure of Nanocrystalline, Partially Disordered MoS$_{2+δ}$ Derived from HRTEM—An Abundant Material for Efficient HER Catalysis
Ronge, Emanuel ; Hildebrandt, Sonja ; Grutza, Marie-Luise ; Klein, Helmut ; Kurz, Philipp ; Jooss, Christian
Citable Link (URL):http://resolver.sub.uni-goettingen.de/purl?gs-1/17511
Journal Article (Published version)
First published (peer reviewed)
Catalysts 2020; 10(8) p.1-16: Art. 856
Abstract
Molybdenum sulfides (MoS$_x$, x > 2) are promising catalysts for the hydrogen evolution reaction (HER) that show high hydrogen evolution rates and potentially represent an abundant alternative to platinum. However, a complete understanding of the structure of the most active variants is still lacking. Nanocrystalline MoS$_{2+δ}$ was prepared by a solvothermal method and immobilized on graphene. The obtained electrodes exhibit stable HER current densities of 3 mA cm$^{−2}$ at an overpotential of ~200 mV for at least 7 h. A structural analysis of the material by high-resolution transmission electron microscopy (HRTEM) show partially disordered nanocrystals of a size between 5–10 nm. Both X-ray and electron diffraction reveal large fluctuations in lattice spacing, where the average c-axis stacking is increased and the in-plane lattice parameter is locally reduced in comparison to the layered structure of crystalline MoS$_2$. A three-dimensional structural model of MoS$_{2+δ}$ could be derived from the experiments, in which [Mo$_2$S$_{12}$]$^{2−}$ and [Mo$_3$S$_{13}$]$^{2−}$ clusters as well as disclinations represent the typical defects in the ideal MoS$_2$ structure. It is suggested that the partially disordered nanostructure leads to a high density of coordinatively modified Mo sites with lower Mo–Mo distances representing the active sites for HER catalysis, and, that these structural features are more important than the S:Mo ratio for the activity.
Sponsor:
Open-Access-Publikationsfonds 2020
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