Controlled Moderate Interfacial Reaction Facilitates High‐Strength Low‐Resistivity Barrier Layer for Half‐Heusler Thermoelectrics

Half-Heusler compounds serve as a compelling solution for medium- and high-temperature waste heat recovery owing to their exceptional thermal stability and superior thermoelectric properties. However, the practical application of their corresponding thermoelectric devices has long been constrained by thermal stress-induced cracking, particularly at the interface between electrodes and thermoelectric material. Here, we engineer an atomically bonded interface via a well-controlled interfacial reaction and propose a novel barrier layer design paradigm based on the thermodynamic parameters. By screening thermodynamic parameters, we have successfully fabricated a ZrNiSn/Co₂₅Fe₅₀Ni₂₅ thermoelectric junction exhibiting high bonding strength (77.0 MPa), low contact resistivity (1.16 µΩ·cm²), and excellent thermal stability at 923 K. The corresponding single-leg device achieves a power density exceeding 6.78 W/cm² and a conversion efficiency of over 6.13%. After annealing at 923 K for 168 h, the junction maintains a bonding strength of 60.0 MPa and a contact resistivity less than 5 µΩ·cm². These results underscore the pivotal role of controlled interfacial reactions in advancing medium- and high-temperature half-Heusler thermoelectric devices, providing a solid foundation for waste heat recovery applications.