This review explores the recent progress on carbon xerogels (CXs) and highlights their development and use as efficient electrodes in organic electric double-layer capacitors (EDLCs). In addition, this work examines how the adjustment of synthesis parameters, such as pH, polymerization duration, and the reactant-to-catalyst ratio, crucially affects the structure and electrochemical properties of xerogels. The adaptability of xerogels in terms of modification of their porosity and structure plays a vital role in the improvement of EDLC applications as it directly influences the interaction between electrolyte ions and the electrode surface, which is a key factor in determining EDLC performance. The review further discusses the substantial effects of chemical activation with KOH on the improvement of the porous structure and specific surface area, which leads to notable electrochemical enhancements. This structural control facilitates improvement in ion transport and storage, which are essential for efficient EDLC charge–discharge (C–D) cycles. Compared with commercial activated carbons for EDLC electrodes, CXs attract interest for their superior surface area, lower electrical resistance, and stable performance across diverse C–D rates, which underscore their promising potential in EDLC applications. This in-depth review not only summarizes the advancements in CX research but also highlights their potential to expand and improve EDLC applications and demonstrate the critical role of their tunable porosity and structure in the evolution of next-generation energy storage systems.

Plastic pyrolysis is widely used to treat polyolefin-rich waste; however, wax byproducts generated during these processes are typically regarded as low-value intermediates. Here, a byproduct-compatible upcycling strategy is proposed to convert polyethylene (PE) pyrolysis wax into activated carbon, enabling integration of functional carbon production into existing recycling value chains. Thermal oxidation was employed to stabilize the wax prior to carbonization, and stabilization at 300 °C yielded a mechanically stable precursor with a high carbon yield. Subsequent carbonization and KOH activation at 900 °C produced an activated carbon (PEWax_AC) with a specific surface area of 1704 m²/g, exceeding that of a representative commercial activated carbon (1575 m²/g). Microstructural analysis revealed predominantly amorphous carbon with locally ordered domains. In symmetric supercapacitor cells, PEWax_AC exhibited higher capacitance at low rates and superior rate capability at high scan rates and current densities, along with reduced charge-transfer resistance. Specifically, PEWax_AC delivered a specific capacitance of 22.9 F/g at 5 mV/s and exhibited a rate retention of 18.6% from 0.1 to 7.0 A/g. These findings demonstrate that plastic pyrolysis wax is a viable and scalable carbon precursor for high-performance supercapacitor electrodes.