Olive-pomace-derived carbons for electrochemical energy storage: feedstock-process-structure-performance relationships

The increasing demand for sustainable and high-performance electrochemical energy-storage technologies has stimulated growing interest in biomass-derived carbon materials. Among agro-industrial residues, olive pomace represents an abundant and chemically versatile lignocellulosic feedstock whose valorization can contribute simultaneously to waste management, resource recovery, and the development of sustainable electrode materials. This review provides a critical and comprehensive assessment of olive-pomace-derived carbons for electrochemical energy-storage applications, with particular emphasis on the relationships between feedstock composition, synthesis strategy, structural properties, surface chemistry, and electrochemical performance. The main conversion routes, including pyrolysis, hydrothermal carbonization, physical activation, and chemical activation using KOH, ZnCl 2 , H 3 PO 4 , and K 2 CO 3 , are examined with respect to their effects on porosity, structural ordering, heteroatom functionality, and electrical conductivity. Particular attention is given to the distinct requirements of electric double-layer capacitors, pseudocapacitive and hybrid systems, and lithium (sodium)-ion battery anodes. Chemical activation generates highly porous carbons with competitive capacitance, whereas high-temperature carbonization favors turbostratic hard-carbon structures suited to sodium storage. However, the analysis also shows that high specific surface area alone is not a reliable predictor of electrochemical performance, as pore accessibility, pore-size distribution, surface chemistry, electrical conductivity, electrolyte composition, and electrode architecture play interconnected roles. A comparative benchmarking of reported materials further highlights significant differences in testing conditions. Finally, the review identifies major challenges related to feedstock variability, process optimization, chemical and energy consumption, scalability, techno-economic feasibility, and life-cycle impacts. Future research should therefore move beyond material-level optimization toward reproducible synthesis, robust processing tolerant to feedstock variability, green activation, rational heteroatom engineering, advanced electrolyte and electrode design, and integrated biorefinery approaches. Olive pomace-derived carbons consequently offer a promising platform for sustainable energy storage, provided that their environmental, economic, and electrochemical advantages are rigorously demonstrated at realistic device and process scales.