Electron‐Delocalized Cu–S–Fe on High‐Conductivity Lignin Carbon Fiber Enables Efficient HMF Conversion

The rational design of robust electrocatalysts for biomass valorization is hindered by poor metal dispersion and sluggish charge transfer. Here, we report a lignin‐assisted electrospinning strategy to construct Cu‐doped FeS 2 heterostructures anchored on N‐doped lignin‐derived carbon fibers (Cu–FeS 2 /LCF). Lignin serves not only as a sustainable carbon precursor but also as a structural regulator that yields conductive, N‐doped carbon fibers capable of uniformly immobilizing ultrasmall Cu–FeS 2 domains. Aberration‐corrected TEM, x‐ray absorption fine structure, and DFT confirm the highly dispersed Cu‐containing species and interfacial coupling between Cu–FeS 2 and the carbon matrix. The electronically activated Cu–S–Fe interface modulates the local reaction environment at Fe 2+ sites, rebalancing the energy barriers for HMF adsorption, HMF* dehydrogenation, and *OH desorption. This promotes –OH‐mediated oxidation of HMF, enabling nearly complete HMF conversion with 98% FDCA selectivity in 1.5 h. DFT further shows that Cu incorporation accelerates electron transfer, while the N‐doped carbon fibers enhance HMF adsorption and reduce the activation energy of HMFOR. Overall, Cu–FeS 2 /LCF establishes a durable and efficient electrocatalyst platform for biomass upgrading and demonstrates lignin‐enabled fiber engineering as a general strategy for designing advanced heterogeneous electrocatalysts.