From polyethylene terephthalate waste to a multilayer MOF: a sustainable strategy for enhanced supercapacitor performance.

The escalating demand for high-performance energy storage systems necessitates the development of electrode materials that synergistically combine high capacity, rate capability and long-term durability. Metal-organic frameworks (MOFs) offer exceptional structural tunability and redox activity but are often limited by dense particle packing and restricted ion diffusion. Here, we report a rationally designed La-Fe-La multilayer MOF electrode constructed via a sequential MOF-on-MOF growth strategy using a benzenedicarboxylic acid linker derived entirely from post-consumer polyethylene terephthalate (PET) waste. This sustainable architecture transforms the morphology from bulky nanoparticles to a hierarchical flower-like nanosheet network, substantially increasing electroactive site accessibility and shortening ion diffusion pathways. The multilayer electrode delivers a remarkable specific capacity of 341.6 C g-1 at 1 A g-1-more than double that of the pristine La-MOF (168.6 C g-1)-while retaining 95.0% of its initial capacitance after 5000 cycles. Kinetic analysis reveals a mixed charge-storage mechanism with increasing surface-controlled contribution at higher scan rates (reaching 56% at 100 mV s-1), while EIS confirms reduced charge-transfer resistance and enhanced ion diffusion. This work establishes multilayer engineering as a powerful strategy to overcome intrinsic limitations of conventional MOFs and demonstrates a scalable, waste-to-energy pathway for next-generation supercapacitor electrodes.