Visualizing the structural evolution of individual active sites in MoS2 during electrocatalytic hydrogen evolution reaction

Understanding the structural evolution of individual active sites during a reaction is a long-standing target in surface science and catalysis. It is still challenging to precisely characterize in situ the intrinsic nature and evolution of the active site because the active site is too small for characterization techniques to decipher the local properties. Here we used electrochemical tip-enhanced Raman spectroscopy to monitor the geometric and electronic evolution of individual active sites of MoS2 during the hydrogen evolution reaction. Reconstruction regions of 40 nm with varied lattice and electron density from the edge to the nearby basal plane were observed during the hydrogen evolution reaction. We further revealed the progressive generation of active sites during the activation process. The synergistic reconstruction around edge due to the lattice deformation reduces the activation energy barriers and promotes the electrocatalytic reaction. These discoveries offer insights into our understanding of the active site and its dynamics during electrocatalysis. Electrocatalysts are often dynamic and their surface structure changes under working conditions. Now the dynamic evolution of MoS2 edges is monitored with nanometre-resolution via electrochemical tip-enhanced Raman spectroscopy during the hydrogen evolution reaction.