Host-Guest Chemistry Creates an Oriented Shuttle Channel to Overcome Mass Transport Limitations in Electrocatalytic Hydrogenation.

Electrocatalytic hydrogenation offers a promising route to value-added chemicals, yet mass transport limitations at industrial current densities remain a critical challenge. Here, we introduce a cyclodextrin-regulated interfacial microenvironment that delivers a Faradaic efficiency (FE) of up to 88% for pyrazine hydrogenation at -100 mA cm-2. The hydroxyl-rich outer surface disrupts the ordered hydrogen-bond network by inhibiting the reorientation of interfacial H2O, facilitating the migration of the reactant to the electrode surface. Simultaneously, the hydrophobic cavities selectively recognize and bind substrates via host-guest interactions, creating oriented shuttle channel that lowers the transfer energy barrier and accelerates mass transport kinetics. This strategy can be extended to diverse hydrogenation reactions and to other deuteration reactions with improved FE at -100 mA cm-2. Moreover, the synthesis of deuterated piperazines and their conversion into deuterium-labeled drugs highlights their practical potential. This work provides a general interfacial engineering strategy to overcome mass transport bottlenecks in electrosynthesis, with broad implications for the production of high-value chemicals and isotopically labeled compounds.