Bio-derived lignin nanospheres as active interfacial regulators in defect-rich W₁₈O₄₉ electrochromic nanocomposites

Designing robust organic-inorganic interfaces is essential for resolving the kinetics-stability trade-off in electrochromic (EC) smart-window materials. Here, bio-derived lignin nanospheres (LNS) are used as active interfacial regulators for defect-rich W₁₈O₄₉ nanowires. Coordination-associated interactions between LNS and W₁₈O₄₉ are accompanied by changes in the local electronic environment and oxygen-vacancy-related defect states. The optimized W₁₈O₄₉/LNS film delivers an optical modulation of 76.1 ± 0.8% at 654 nm, a coloration efficiency of 31.7 ± 1.1 cm² C^-1, and a bleaching time of 7 ± 1 s, together with improved cycling retention. Semi-quantitative W L₃-edge X-ray absorption analysis indicates a decrease in the estimated average W oxidation state from 3.29 to 2.89. Operando FT-IR spectroscopy and DFT calculations reveal bias-induced changes in the interfacial redox and solvation environment, while ESR and electrochemical kinetic analyses support defect modulation and an increased surface-controlled contribution. These findings establish bio-derived interfacial regulation as a promising strategy for defect-rich functional oxide nanocomposites.