Researchers Turn Waste Polystyrene Into Hydrogen Storage

Abstract

To address the dual challenges of plastic waste management and sustainable hydrogen storage, we propose an innovative strategy to upcycle post-consumer polystyrene (PS) waste into liquid organic hydrogen carriers (LOHCs). The process involves pyrolyzing PS into aromatic monomers, primarily styrene, which are subsequently hydrogenated into cyclic hydrocarbons such as ethylcyclohexane. Dehydrogenation of these hydrogen-rich LOHCs releases high-purity hydrogen, with catalytic performance strongly influenced by the properties of supported Pt catalysts. Among various supports, Pt catalysts on nanosheet-assembled Al2O3 demonstrated superior activity and stability, attributed to a higher proportion of metallic Pt0 species, low surface acidity, and enhanced pore structures. However, polycyclic compounds in the PS-derived LOHCs led to catalyst deactivation via coke formation, necessitating a distillation step to remove these precursors. Integration of distillation, energy recovery, and LOHC recycling were shown to maintain catalyst longevity and process efficiency. Life cycle assessment and techno-economic analysis confirmed that upcycling PS waste into LOHCs offers both environmental benefits, including a negative carbon footprint for LOHC production, and economic viability, with competitive hydrogen transport costs. This work not only presents a feasible route for converting PS waste into valuable energy carriers but also contributes to advancing circular carbon strategies and the hydrogen economy.

A research team, affiliated with UNIST has unveiled a novel technology that enables hydrogen to be stored within polystyrene-derived materials, particularly those originating from Styrofoam. This advancement not only offers a solution to the low recycling rate of polystyrene-less than 1%-but also makes hydrogen storage and transportation more practical and accessible, addressing the challenges associated with handling gaseous hydrogen.

Led by Professor Kwangjin An from the School of Energy and Chemical Engineering at UNIST, in collaboration with Dr. Hyuntae Sohn from KIST and Professor Jeehoon Han from POSTECH, the team successfully designed a comprehensive, closed-loop system to convert waste polystyrene into a liquid organic hydrogen carrier (LOHC). This innovative process enables efficient hydrogen storage, retrieval, and reuse.

LOHC molecules store hydrogen within their cyclic chemical structure, allowing safe, stable storage at room temperature and pressure. Their liquid form facilitates long-term storage and is compatible with existing oil transportation infrastructure-making this approach particularly promising for the hydrogen economy.

The reported approach exploits the aromatic-rich structure of polystyrene. When heated, polystyrene decomposes into low-molecular-weight aromatic compounds such as styrene and toluene. These compounds react with hydrogen at elevated temperatures to store hydrogen, which can later be released via catalytic dehydrogenation.

Catalysts are central to this process. Ruthenium catalysts facilitate hydrogen absorption, while platinum catalysts enable hydrogen release. Notably, the researchers discovered that the catalytic performance of platinum-supported catalysts varies significantly depending on the support structure. Among various options, nanosheet-assembled aluminum oxide demonstrated remarkable reactivity and stability, improving hydrogen release efficiency.

To prevent catalyst deactivation due to impurity buildup, the team implemented a distillation step to selectively remove polycyclic compounds and other contaminants, thereby extending catalyst lifespan and ensuring process durability.

Additionally, the researchers optimized the process for energy efficiency and economic viability by utilizing waste heat generated during the reaction-through the combustion of residual byproducts-reducing external energy consumption and increasing the throughput of polystyrene waste conversion.

Commenting on their findings, the research team stated, "This is the first-ever demonstration of converting waste polystyrene into a practical hydrogen storage medium. Our approach tackles two significant environmental challenges-plastic waste recycling and hydrogen storage-simultaneously." They further added, "We believe this technology has strong potential for industrial application and policy development in the future."

This research was supported by the Ministry of Science and ICT (MSIT), the National Research Foundation of Korea (NRF), and the Engineering Research Center (ERC) of Excellence Program. The findings were published as a back cover of the August 2025 issue of ACS Catalysis.

Journal Reference

Hyeongeon Lee, Yoondo Kim, Heedo Ryou, et al., "Upcycling Post-Consumer Polystyrene Waste into Liquid Organic Hydrogen Carriers," ACS Catal., (2025).