Publication of the Chemistry Laboratory in the journal ACS Catalysis on November 9, 2023. Communication of CNRS Chemistry on November 27, 2023.
Producing dihydrogen by electrolysis of water requires rare and therefore expensive catalysts. They could be replaced by another molybdenum-based catalyst, much more abundant but currently less efficient. Scientists are therefore trying to elucidate how it works, in order to improve its performance. A study by teams from the Chemistry Laboratory (CNRS/ENS de Lyon) and IFP Énergies nouvelles (IFPEN), published in ACS Catalysis.
Amorphous MoS3 (a-MoS3) is an appealing low-cost catalyst for the hydrogen evolution reaction (HER), which is a promising process for electrocatalytic hydrogen generation. In this study, we scrutinize the stability and HER catalytic activity of carbon-supported Mo3S9-x-clusters under electrochemical conditions by using grand-canonical density functional theory (GC-DFT) coupled with a cluster-continuum solvation strategy. We show that some sulfur atoms of the Mo3S9 cluster can be removed as H2S under HER conditions. This partial desulfurization leads to a stable working state of Mo3S8 or Mo3S7 with HER catalytic activity at moderate thermodynamic overpotentials. The desulfurization process simultaneously induces water adsorption on undercoordinated molybdenum sites. The so-formed hydrated Mo3S9-x-clusters can exhibit two distinct active sites. On Mo3S8(H2O)2, the top SH* species are active for the HER, whereas OH* species are involved in the HER on Mo3S7(H2O)3. By comparison with a previous study of the HER catalyzed by 2H-MoS2 edge sites, we demonstrate that S-defective a-MoS3 is an efficient HER electrocatalyst. Moreover, in contrast to active sites on 2H-MoS2, the HER mechanism on Mo3S9-x-clusters involves a protonation step instead of the common proton-coupled electron transfer, an elementary reaction step that required GC-DFT to be identified.
ReferenceElectrochemical Potential-Dependent Stability and Activity of MoS3 during the Hydrogen Evolution Reaction. Nawras Abidi, Amit Sahu, Pascal Raybaud, and Stephan N. Steinmann. DOI : 10.1021/acscatal.3c03292
Illustration credits: iStock, peterschreiber.media