A new electrochemical system efficiently converts PET plastic waste into glycolic acid and hydrogen, using alternating pulses and a stable alloy nanocatalyst to enable continuous, membrane-free operation.
(Nanowerk Spotlight) Plastic waste is now so deeply embedded in the environment that microplastics are found in drinking water, soil, and even human blood. Polyethylene terephthalate (PET), used in bottles, textiles, and food packaging, is a major contributor. Its durability, while useful in products, creates long-term pollution once discarded.
Conventional recycling methods, which mostly involve remelting, often degrade material quality and cannot keep pace with the growing volume of waste. At the same time, demand is increasing for cleaner sources of chemical feedstocks and hydrogen, a gas central to emerging low-carbon energy systems.
One proposed solution links these problems: using electrochemical methods to break down PET waste and convert its components into valuable products. A key target is ethylene glycol (EG), a compound released when PET is hydrolyzed in alkaline solution. This molecule can be selectively oxidized to glycolic acid (GA), a valuable chemical used in bioplastics, skincare, and pharmaceuticals.
Moreover, the same system could produce hydrogen at the cathode, creating a dual benefit. But the technology is not yet robust or efficient enough for large-scale use. The catalysts needed to drive these reactions—typically noble metals like platinum and palladium—are prone to rapid deactivation. Surface poisoning and metal oxidation reduce efficiency within minutes, especially under high current conditions required for industrial processing.
To extend catalyst life, pulsed electrochemical strategies have been developed, allowing the surface to periodically recover. These approaches, while helpful, come with a trade-off: during the “resting” phases of the cycle, no useful reaction occurs. This lowers charge efficiency and prolongs processing time. At scale, such inefficiencies translate to higher energy costs and limited throughput.
High-entropy alloys (HEAs) offer a materials-based route to improved performance. These are solid solutions made from five or more metals, whose mixed atomic structure gives rise to stability, corrosion resistance, and tunable surface chemistry. Combined with better control of operating conditions, HEAs could help resolve the tension between activity, selectivity, and durability. Yet so far, there has been no integrated solution that pairs these materials with an optimized operating protocol to fully exploit their capabilities in PET upcycling.
The innovation centers on a mesoporous film made from five metals—platinum, palladium, gold, silver, and copper—deposited onto a nickel foam substrate. The resulting material, termed m-HEA/NF, features a highly porous structure that maximizes the number of active sites and enhances mass transport. More importantly, it serves a dual role in the electrochemical cell: oxidizing ethylene glycol to glycolic acid at the anode while simultaneously producing hydrogen at the cathode.
Schematic illustration of traditional (a) static, (b) pulse, and (c) new ALT pulse system. Production is abbreviated as Pro. (Image: reprinted with permission by Wiley-VCH Verlag)
The key feature of the ALT strategy is its continuous switching between anodic and cathodic potentials. In the anodic phase, the catalyst drives the oxidation of EG to GA. In the cathodic phase, the same electrode surface undergoes a mild reduction step. This not only regenerates the metallic state of the catalyst by removing surface oxides but also produces hydrogen. This alternation ensures that the active surface is regularly restored while the system remains productive at all times—avoiding the inefficient “resting” stages of earlier pulse systems.
This dual-function approach achieved a Faradaic efficiency of 97 percent for glycolic acid and nearly 100 percent for hydrogen at a current density of 250 milliamperes per square centimeter. Faradaic efficiency refers to how effectively electrical charge is used to form the desired products—in this case, GA and hydrogen—rather than being wasted. The system also delivered high production rates: over 2 millimoles of GA and 108 milliliters of hydrogen per square centimeter per hour. Compared to traditional pulsed methods, this represents a doubling of output while maintaining high selectivity and stability.
To understand the stability of this catalyst under long-term operation, the researchers conducted in-depth structural and spectroscopic studies. Electron microscopy confirmed the uniform distribution of the five metals and the preservation of the porous structure after extended use. X-ray photoelectron spectroscopy showed that surface oxides formed during the anodic phase were effectively reduced during the cathodic cycle. This confirmed the ability of the ALT pulses to regenerate the active metallic surface repeatedly.
In situ Raman and infrared spectroscopy provided further insight. These techniques revealed that intermediate species—molecules that can temporarily block catalytic sites—accumulated during the anodic phase but were effectively removed during the cathodic phase. Simulations supported this, showing how alternating potentials help disperse reaction products and prevent their buildup near the electrode surface.
Electronic structure calculations helped explain why this high-entropy alloy performs better than single-metal catalysts. The mixing of elements like Pd, Pt, Cu, and Ag alters the electronic states at the surface. This tuning of electronic properties allows for a better balance between adsorbing reaction intermediates and releasing final products.
For hydrogen production, the alloy showed nearly ideal hydrogen binding energy, meaning it can both form and release hydrogen efficiently. For glycolic acid production, the reaction pathway had a lower energy barrier compared to that on pure palladium, further confirming the advantage of the alloyed surface.
The researchers also tested the system in a membrane-free flow reactor, which simplifies design and reduces cost. Membranes are typically used in electrolysis cells to separate products from the anode and cathode, but they add complexity and expense. The ALT system showed no evidence of cross-reactions between products at the two electrodes, meaning the membrane could be safely omitted. The setup was scaled up to deliver a current of 2 amperes with stable operation, demonstrating its potential for industrial application.
Long-term operation over 100 hours confirmed that the ALT pulse system could maintain high output and selectivity without structural degradation. A techno-economic analysis based on realistic market assumptions projected a net revenue of over 1200 US dollars per ton of processed PET, accounting for the sale of both glycolic acid and hydrogen. This positions the system as not only technically feasible but also economically competitive.
This study demonstrates how careful integration of material design, electrochemical control, and system architecture can overcome long-standing challenges in PET upcycling. By eliminating inefficient rest periods and stabilizing catalyst activity through dynamic regeneration, the alternating pulse strategy achieves continuous, scalable operation. The dual-function high-entropy alloy catalyst plays a central role, enabling both reactions to proceed in a single system. This approach advances the feasibility of electrochemical recycling technologies that are both sustainable and commercially viable.
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