Influence of compositional tuning on the power density of porous Zr-MOF/polyaniline hybrid flexible thermoelectric generators for waste-heat harvesting

The unique and promising thermoelectric properties of porous zirconium-metal-organic frameworks (Zr-MOFs) and conducting polymers are attracting increasing attention for the fabrication of eco-friendly, flexible thermoelectric generators. Achieving electrical conductivity in porous and insulating metal-organic frameworks requires infiltrating the pores with conductive guest molecules. However, the thermoelectric behaviour of Zr-MOF and polyaniline hybrid materials is not explored for screen-printed devices. Hence, this work presents, for the first time, the in-situ polymerisation and application of conducting polyaniline incorporating a Zr-MOF-based material for the fabrication of flexible thermoelectric generators, as per our literature review for low-grade temperature applications. Novel screen-printing inks for mass production were formulated using a cellulose-based bio-binder, incorporating Zr-MOF into a polyaniline matrix at varying concentrations. The presence of an optimum 5 % of Zr-MOF significantly tuned mobility, carrier concentration, bandgap, microstructure, and resistivity of polyaniline, resulting in the highest Seebeck coefficient of 57.02 μV/K and a power output of 0.504 nW at a temperature gradient of 65 K, which was 12.6 times higher than that of pure Polyaniline. This optimized concentration resulted in a power density of 0.288 mW/m². Furthermore, an 8-leg, p-n type flexible thermoelectric generator, incorporating MnO₂ as n-type legs, exhibited a power output and power density of 156.5 nW and 89.1 mW/m², respectively, at a temperature gradient of 65 K. The fabricated devices demonstrated good energy harvesting at low-grade temperatures and high mechanical flexibility, making them a potential candidate for use in wearable electronics and low-grade-temperature energy-harvesting systems. Further enhancement of power density can be achieved by connecting multiple FTEG's in series.