Enhanced Heat Transfer for Thermomagnetic Generation in Low‐grade Waste Heat Harvesting

Thermomagnetic generation (TMG) is a potential technology for harvesting low-grade waste heat. However, the limited heat transfer of TMG materials constrains their practical performance. In this study, low-melting point metal indium (In) with high thermal conductivity is introduced into a Ni─Mn─In Heusler alloy to fabricate Ni─Mn─In/In TMG composites. The thermal conductivity increased significantly from 14.86 W m^-1 K^-1 for the Ni─Mn─In alloy to 65.2 W m^-1 K^-1 for the Ni─Mn─In/In composite. The composite containing 40 wt.% In (In40) exhibits superior TMG performance, with an average voltage of 2.38 mV g^-1, a maximum power density of 0.433 µW g^-1, and a cost index of 0.116 µW per CNY, which are 3.8, 2.4, and 1.1 times higher than those of the Ni─Mn─In alloy. By further changing the geometry, a 2 mm thick In40 with 7 holes achieves a thermal conductivity 15 times higher and a power generation index 8 orders of magnitude greater than those of other reported TMG materials. The combination of enhanced TMG performance and improved heat transfer, along with zero thermal hysteresis, good machinability, high corrosion resistance, and long-term cycle stability, makes this composite a strong candidate for low-grade waste heat recovery applications.