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.