Dual Co Sites in n─n Type Heterojunction Enable Selective Electrochemical Co‐Valorization of HMF and CO 2

Abstract Electrocatalytic oxidation of biomass‐derived hydroxymethylfurfural (HMF) to 2,5‐furandicarboxylic acid (FDCA) and electrocatalytic reduction of CO 2 into CO are two highly investigated areas. Efficient electrocatalytic system design that combines CO 2 valorization with biomass upgrading offers a viable solution to produce high‐value chemicals and renewable energy at the same time. Here, we demonstrate an interfacial‐engineered CoS/Co─N─C n─n type heterojunction featuring unique dual Co sites and strong built‐in electric field (BEF) effects, which enables efficient electrochemical coupling of 5‐hydroxymethylfurfural oxidation reaction (HMFOR) and CO 2 reduction reaction (CO 2 RR). The optimized catalyst achieves exceptional performance metrics, i.e., a record‐low onset potential of 1.12 V (versus RHE), with 99% selectivity and 98.2% faradaic efficiency (FE) for 2,5‐furandicarboxylic acid (FDCA) in HMFOR, coupled with 98.6% CO 2 ─to─CO selectivity and the FE average was retained 98.4% in CO 2 RR, which outperform the previously reported state‐of‐the‐art electrocatalysts. Moreover, the integrated HMFOR//CO 2 RR system demonstrates impressive stability over 50 h continuous operation. Through systematic experimental examination and theoretical calculations, we reveal that the BEF boosts the formation of the unique dual Co coordination environments (Co─N 4 electron‐deficient and Co─S electron‐rich configurations) through modulation of charge transport dynamics, facilitating HMF activation through *OH intermediate stabilization while promoting multi‐electron CO 2 reduction via charge accumulation. This work establishes a blueprint for developing multi‐functional catalytic architectures that address the thermodynamic and kinetic challenges in coupled electrochemical systems, advancing the frontier of sustainable electrosynthesis technologies.