<p>Heterogeneous molecular catalysts have emerged as promising platforms for electroreduction reactions, yet their performance is limited by inefficient interfacial electron transfer across poorly coupled molecule–electrode interfaces. Here we report an interfacial engineering strategy using oxygen-functionalized ketjenblack as an electronic bridge to mitigate this interfacial barrier between spatially distorted copper phthalocyanine and the carbon matrix, enabling efficient electrochemical C–C coupling of benzaldehyde to achieve a hydrobenzoin production rate of 0.62 mmol h⁻¹ cm⁻². Experimental and theoretical analyses elucidate that the reinforced conjugation promotes *ketyl intermediate formation and drives subsequent C–C coupling through nucleophilic attack on benzaldehyde. The nucleophilicity index (<i>f</i>⁺) of aldehyde groups is identified as a key descriptor governing both reaction kinetics and stereoselectivity, where higher <i>f</i>⁺ values correlate with accelerated reduction rates and improved stereochemical outcomes. This interfacial modulation strategy is validated through enhanced performance in N=N coupling of nitrobenzene, CO₂ electroreduction and nitrite reduction. This work provides a general approach to regulate efficient molecular–electrode interfaces, addressing a key bottleneck in heterogeneous electrocatalysis.</p><p></p>