Dual Co sites in n‐n type heterojunction enable selective electrochemical co‐valorization of HMF and CO2

Electrocatalytic oxidation of biomass‐derived hydroxymethylfurfural (HMF) to 2,5‐furandicarboxylic acid (FDCA) and electrocatalytic reduction of CO2 into CO are two highly investigated areas. Efficient electrocatalytic system design that combines CO2 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 CO2 reduction reaction (CO2RR). The optimized catalyst achieves exceptional performance metrics, i.e., a record‐low onset potential of 1.12 V (vs. RHE), with 99% selectivity and 98.2% faradaic efficiency (FE) for 2,5‐furandicarboxylic acid (FDCA) in HMFOR, coupled with 98.6% CO2‐to‐CO selectivity and the FE average was retained 98.4% in CO2RR, which outperform the previously reported state‐of‐the‐art electrocatalysts. Moreover, the integrated HMFOR//CO2RR system demonstrates impressive stability over 50‐hour 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‐N4 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 CO2 reduction via charge accumulation.