Powering the future: emerging role and mechanistic insights of polyoxometalates in piezo- and triboelectric energy materials

In recent years, the design of advanced piezoelectric and triboelectric nanogenerators (PENGs and TENGs) has gained significant momentum as a sustainable strategy for harvesting mechanical energy from the environment. A central approach to improve their performance involves the incorporation of functional fillers into host matrices, enabling enhancement of charge transport, dielectric properties, and interfacial stability. While numerous studies have focused on organic and inorganic fillers, polyoxometalates (POMs) remain an underexplored yet exceptionally promising class of multifunctional components. POMs exhibit unique structural diversity, highly tunable redox chemistry, strong electron-accepting ability, and rich opportunities for chemical modification, making them versatile platforms for tailoring energy conversion processes. This review provides a comprehensive discussion of recent progress in integrating POMs into piezoelectric and triboelectric materials, including ceramics, polymers, and composite systems. We highlight mechanistic insights into how variations in POM composition, heteroatoms, addenda atoms, counter-cations, and framework architectures influence dielectric response, electron transfer, and energy-harvesting efficiency. Furthermore, emphasis is placed on structure-property-performance correlations, revealing how rational design of POM-based fillers can yield NGs with higher output power, improved durability, and multifunctional capabilities. Beyond material optimization, POMs also open pathways for designing next-generation energy devices that exploit synergistic piezo-triboelectric effects, offering potential for self-powered electronics, wearable sensors, and green energy technologies. Overall, the review underscores the transformative role of POM-based fillers in advancing the frontiers of energy harvesting. By outlining future research opportunities, it aims to guide the development of innovative POM-enabled NGs for sustainable and scalable applications.