Unlocking the ignored triboelectric potential of fly ash: Random hierarchical micropatterned ultra-tough PVA composites for super-amplified energy harvesting in smart wearable and security applications

초록

Fly ash (FA), a hazardous byproduct of coal burning, poses serious environmental and health risks due to its large-scale production, improper disposal and inadequate strategies for sustainable recycling. Every year, millions of tons of FA are produced and landfilled, significantly contributing to environmental pollution. Although FA has been extensively utilised in the construction industry, its incorporation into polymer composites remains challenging due to its various particle sizes, complex surface chemistry, poor compatibility, and non-uniform dispersion within polymer matrices. For the first time, we have created an ultra-tough polyvinyl alcohol (PVA)/FA composite exhibiting outstanding improvements, similar to 475% in elongation at break and similar to 626% in toughness compared to neat PVA film. Such high mechanical properties were achieved via tailoring surface chemistry, mixing strategies, and process optimisation. Furthermore, the composite demonstrates excellent potential for self-powered energy-harvesting devices, such as triboelectric nanogenerators (TENGs) and smart wearables. A hierarchical-random-micro-pattern, produced by sandpaper embossing on the composite surface and treated with in-situ ethylenediamine (EDA), increased device performance by 6.7-9.2-fold. A compact 3.06 cm(2) device achieved a V-OC of 184.7 V, I-SC of 17.6 mu A, and a power density of 1850 mW/m(2), surpassing many recent benchmarks. The device charged 2.2 and 4.7 mu F capacitors in just 13 and 18 s, respectively, and maintained about 98.8% efficiency over 12,500 cycles, remaining operational after 73 days. All underlying mechanisms were systematically explored. These results demonstrate that hazardous FA can be effectively valorised into high-performance composites and next-generation energy harvesting devices.

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