Upcycling Agro-Food Industrial Biomass Waste into Functional Activated Carbon for Selective CO2 Capture and Supercapacitor Applications

Abstract Activated carbon (AC) materials were developed via a single-step method from three different biowaste sources and tailored for application in carbon dioxide (CO2) capture and electrochemical energy storage, combining the concept of biowaste valorisation with sustainable environmental and energy applications. This work investigated the use of three underexplored agro-food waste streams as precursors, namely flour mill waste (BW1), old corn waste (BW2), and feed waste (BW3), and performed a systematic comparison of their conversion under the same activation conditions, as well as characteristics and performance. The developed AC materials demonstrated properties such as high graphitization, favorable pore-structure configuration and surface area, and favorable surface characteristics. CO2 adsorption experiments at 298 K showed a capacity of 2.55 mmol/g at 1 bar with stability over multiple cycles for AC2, as well as high CO2/N2 selectivity, reaching 48 at 1 bar (ideal adsorbed solution theory (IAST)) for a 15:85 v/v CO2/N2 mixture for AC1, suggesting a high selective affinity for CO2 capture at ambient conditions. Furthermore, electrochemical experiments revealed stable performance as electric double-layer capacitors as a result of low solution and charge-transfer resistance, demonstrating capacitive performance in the order of 250 F/g at a scan rate of 5 mV/s for AC3, which was tested at different increasing scan rates and determined to retain a capacitance value higher than 90 F/g at a high scan rate of 100 mV/s. Galvanostatic charge−discharge (GCD) investigations revealed virtually symmetric charge−discharge curves with an acceptable rate capability for a symmetric AC3 full cell, retaining ∼70% of initial capacitance despite a 4-fold increase in current density, and preserving ∼78% of initial capacitance after 1000 cycles. These results reveal the potential of agro-industrial waste streams-derived AC materials for selective carbon capture and electrochemical energy storage, enabling them a simple, potentially scalable, and sustainable material platform for such applications. The key contribution is the processing of three previously underutilized agro-food industrial biomass wastes into functional AC materials for energy storage and CO2 capture via a single-step KOH activation approach, allowing for direct comparison and correlation of precursor chemistry. Furthermore, this provides a solid basis for future precursor-specific tuning of KOH loading, activation temperature and time, pore structure, and surface functioning to optimize properties and performance.