Interfacial Molecular Engineering of Cobalt Catalysts Enables Efficient Bifunctional Electrocatalysis

Molecularly defined bifunctional electrocatalysts that operate efficiently across a broad pH range remain a formidable challenge in electrocatalysis. Herein, we present a rationally designed hybrid system that systematically disentangles the distinct roles of molecular anchoring and support functionalization—a critical but previously overlooked distinction in carbon‐based electrocatalyst design. By noncovalently immobilizing cobalt‐cyclen complexes bearing either aromatic (benzyl) or aliphatic side chains onto carboxylated multiwalled carbon nanotubes (MWCNTs‐COOH), we construct molecular–carbon interfaces that allow the relationship between molecular structure and catalytic activity to be examined. The benzyl‐functionalized Co(12‐TBC)/MWCNTs‐COOH hybrid delivers exceptional bifunctional performance, outperforming its aliphatic analog by a striking 358 mV reduction in hydrogen evolution reaction (HER) overpotential at −10 mA cm −2 ( η 10 ) in neutral media, alongside significantly enhanced oxygen evolution reaction (OER) activity. Remarkably, this hybrid maintains impressive activity across acidic ( η 10 = 161 mV for HER, 283 mV for OER) and alkaline (343/359 mV) conditions, underscoring its pH‐universal versatility. Comprehensive electrochemical studies show that surface carboxylation increases accessible active‐site density and improves intrinsic catalytic activity and interfacial electron‐transfer characteristics. This work highlights interfacial molecular organization as an important design parameter and validates noncovalent immobilization as a scalable, broadly applicable strategy for advanced molecular electrocatalysis.