Circumventing Concentration Limitations in Electrocatalytic Hydrogenation of 5‐Hydroxymethylfurfural through Alkali Metal Ion Mediated Supramolecular Control

Performance deterioration in the electrocatalytic hydrogenation (ECH) of concentrated biomass platform molecules remains a major obstacle for practical implementation, largely due to an incomplete understanding of concentration‐dependent mechanisms. Using the 5‐hydroxymethylfurfural reduction reaction (HMFRR) as a model system, we uncover an unanticipated role of intermolecular hydrogen bonding under high reactant concentrations as revealed by constant‐potential DFT calculations and AIMD simulations. Guided by this mechanistic insight, we develop a cation‐modulation strategy and identify Li + ion as the most effective promoter of HMFRR, via a synergistic combination of (i) disruption of intermolecular hydrogen bonds in HMF dimers enabled by the small ionic radius, deep penetration into the inner Helmholtz plane and low coordinated structure of Li + , (ii) enhanced *H transfer arising from its strong electron‐withdrawing character, and (iii) preservation of high HMFRR selectivity at moderate Li + concentrations. Experimental electrochemical measurements and 1 H nuclear magnetic resonance ( 1 H NMR) spectroscopy validate these predictions. This work resolves a long‐standing challenge in high‐concentration ECH and establishes a generalizable paradigm for upgrading concentrated biomass‐derived platform molecules through rational interfacial engineering.