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 FeS₂ heterostructures anchored on N-doped lignin-derived carbon fibers (Cu-FeS₂/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-FeS₂ domains. Aberration-corrected TEM, x-ray absorption fine structure, and DFT confirm the highly dispersed Cu-containing species and interfacial coupling between Cu-FeS₂ and the carbon matrix. The electronically activated Cu-S-Fe interface modulates the local reaction environment at Fe²⁺ 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-FeS₂/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.