Operation mechanism of amorphous molybdenum sulfide catalyst during the H2 evolution investigated by an operando electrochemical quartz crystal microbalance analysis
摘要
Water splitting is considered as the most effective green hydrogen production method in the near future. Among various catalysts, amorphous molybdenum sulfide (MoSx) exhibits itself as an attractive Pt-free catalyst to promote the hydrogen evolution reaction (HER). In this research, we employed electrochemical quartz crystal microbalance (E-QCM) to track the mass fluctuation during HER operation. The mass loss of approximately 20% was recorded while holding the catalyst at -0.11 V vs RHE, indicating the material was activated prior to proton reduction. A drastic increase in HER catalytic performance with the 90 mV shifting of onset potential from −0.23 V vs RHE for pristine MoSx to −0.145 V vs RHE for the activated material was recorded. The current density increases ca. 5 times from 5.02 to 25.02 mA/cm2 at −0.3 V vs RHE (iR correction). The mechanism of catalyst activation was also proposed by the elimination of S atoms from the MoSx polymeric structure generating H2S and [Mo3S7] clusters that may serve as actual active sites for HER. The generated clusters then gradually dissolved in the solution causing catalyst degradation that diminished catalytic performance of MoSx.