| Summary: | Waste heat management holds great promise to create a sustainable and energy-efficient society as well as contributes to the alleviation of global warming. Harvesting and converting this waste heat in order to improve the efficiency is a major challenge. Here we report biomimetic nacre-like hydroxyl-functionalized boron nitride (BN)-polyimide (PI) nanocomposite membranes as efficient 2D in-plane heat conductor to dissipate and convert waste heat at high temperature. The hierarchically layered nanostructured membrane with oriented BN nanosheets gives rise to a very large anisotropy in heat transport properties, with a high in-plane thermal conductivity (TC) of 51 W m−1 K−1 at a temperature of ∼300 °C, 7314% higher than that of the pure polymer. The membrane also exhibits superior thermal stability and fire resistance, enabling its workability in a hot environment. In addition to cooling conventional exothermic electronics, the large TC enables the membrane as a thin and 2D anisotropic heat sink to generate a large temperature gradient in a thermoelectric module (ΔT = 23 °C) through effective heat diffusion on the cold side under 220 °C heating. The waste heat under high temperature is therefore efficiently harvested and converted to power electronics, thus saving more thermal energy by largely decreasing consumption.
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