Upcycling Sugar Cane Biomass into 2G Sugars and Lignin-Derived Biochars for Preparing Carbon-Based Electrodes

Converting lignin into specialty and bulk chemicals enhances both the economic viability and the sustainability of biorefineries. Here, we present an integrated approach to produce monosaccharides, lignin, and lignin-derived biochars from two underutilized agricultural byproducts: sugar cane bagasse and sugar cane straw. Modified kraft and soda pulping yielded digestible pulps, which were readily hydrolyzed into monosaccharides with glucan conversions ranging from 76% to 96%. The corresponding pretreatment liquors provided lignins, which were pyrolyzed to obtain biochars. These biochars were blended with a binder to prepare biochar inks, which were deposited onto electrodes to create functional electrodes. SEM-EDX characterization revealed a higher silicate content in straw-derived biochars and increased sulfur levels in kraft-derived biochars. Such compositional differences influenced electrochemical stability and catalytic activity toward oxygen evolution (OER) and oxygen reduction (ORR) reactions. Bagasse-derived electrodes exhibited modest ORR currents, with onset potentials of 0.82 V (soda) and 0.76 V (kraft). In contrast, straw-derived electrodes displayed pronounced electrochemical instability in alkaline media, limiting their use as catalytic carbons for metal-air batteries. Nonetheless, their higher conductivity suggests potential as conductive additives in insertion-type battery electrodes. Overall, this work illustrates integrated strategies for valorizing agricultural byproducts, expanding the range of applications for lignin-derived materials within biorefinery processes.