Researchers from India's Homi Bhabha National Institute and Bhabha Atomic Research Centre have demonstrated an efficient route for converting high-density polyethylene (HDPE) plastic waste into high-quality turbostratic graphene using flash Joule heating (FJH), while directly validating its performance in supercapacitor electrodes.
The approach relies on rapid capacitive discharge to drive extremely fast resistive heating of the polymer precursor, reaching temperatures above 2500°C within milliseconds. This ultrafast thermal spike induces carbonization and graphitization in a single step, eliminating the need for external furnaces, catalysts, or solvents. Compared to conventional graphene production routes such as chemical vapor deposition or chemical oxidation, the FJH process is significantly simpler, avoids hazardous chemicals entirely, and reduces both energy consumption and environmental impact.
HDPE, a widely used thermoplastic found in packaging and consumer products, represents a major fraction of global plastic waste. Its chemical stability and high molecular weight make it persistent in the environment, contributing to long-term pollution and microplastic formation. Traditional recycling methods often downgrade its value due to polymer degradation, and only a small portion of the more than 400 million tonnes of plastic produced annually is effectively recycled. Converting such waste into graphene offers a compelling upcycling pathway, transforming a low-value pollutant into a high-performance nanomaterial.
Material characterization confirms the high quality of the synthesized graphene. Raman spectroscopy shows a high I2D/IG ratio of 1.22 and a low ID/IG ratio of 0.05, indicating well-ordered graphitic domains with minimal defects. Complementary analyses using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) further validate the formation of turbostratic graphene structures. This form of graphene, characterized by rotational misalignment between layers and increased interlayer spacing, is particularly advantageous for electrochemical applications due to improved ion accessibility.
To demonstrate practical applicability, the researchers fabricated flexible electrodes using functionalized carbon nanotubes (FCNTs) as the current collector and HDPE-derived flash graphene (HDPE-FG) as the active material - without any additional conductive additives. This simplified architecture highlights the intrinsic conductivity and structural integrity of the produced graphene.
Electrochemical testing in a three-electrode configuration revealed strong performance in both alkaline and acidic electrolytes. The HDPE-FG electrodes achieved a specific capacitance of approximately 132.8 F/g in 1 M KOH and 102.5 F/g in 1 M H₂SO₄ at a current density of 0.3 A/g. These results indicate efficient charge storage and rapid energy delivery, consistent with graphene’s high surface area and electrical conductivity. The turbostratic structure likely plays a key role by reducing layer restacking and enhancing electrolyte ion transport.
The underlying mechanism of the FJH process is based on ultrafast Joule heating, where a high-current pulse generates localized temperatures sufficient to break polymer chains and reorganize carbon atoms into sp²-bonded graphene networks. Because the heating and cooling occur on millisecond timescales, the process suppresses the formation of amorphous carbon and promotes graphitic ordering, while also minimizing energy losses.
Overall, this work highlights a scalable and economically attractive pathway for plastic upcycling. By combining rapid, solvent-free synthesis with direct integration into energy storage devices, the study bridges waste remediation and advanced materials engineering, positioning HDPE-derived flash graphene as a promising candidate for next-generation supercapacitors.
