On-Chip Microdevice Unveils Reactant Enrichment Effect Dominated Electrocatalysis Activity in Molecular-Linked Catalysts.

Molecular functionalization has been intensely studied and artificially constructed to advance various electrocatalytic processes. While there is a widely approved charge-doping effect, the underlying action for reactant distribution/transport remains long neglected. Here an on-chip microdevice unravels that the proton enrichment effect at prototypical methylene blue (MB)/MoS2 interfaces rather than charge doping contributes to the hydrogen evolution reaction (HER) activity. Back-gated electrical/electrochemical tests detect quantitatively a strong charge injection from MB to MoS2 realized over diploid carrier density, but these excess carriers are unqualified for the actual enhanced HER activity (from 32 to 125 mA cm-2 at -0.29 V). On-chip electrochemical impedance further certifies that the proton enrichment in the vicinity of MoS2, which is generated by the nucleophilic group of MB, actually dominates the HER activity. This finding uncovers the leading function of molecular-linked catalysts.