Thermal stability of thermoelectric devices plays a pivotal role in their practical applications. Chemical reaction/diffusion between thermoelectric materials and electrodes is one of the primary factors contributing to the degradation/failure of device performance at elevated temperatures. Introducing barrier layers to impede the behavior of chemical reactions has emerged as an effective approach for averting the failure of these devices. In this work, the FeSi is revealed to be a potent material of barrier layer in high-performance Mg₂Si_0.3Sn_0.7 thermoelectric material based on the considerations of interfacial reaction energy and sinterability. The well-established bond in Mg₂Si_0.3Sn_0.7/FeSi joint results in a low contact resistivity of ~20 μΩ⸱cm² and a conversion efficient of ~6.5% for the Mg₂Si_0.3Sn_0.7 single-leg device is achieved at a temperature difference of ~290 K. Long-term measurements of the device at a hot-side temperature of 600 K reveal that the performance remains nearly invariable as time further increases, which suggests that the FeSi layer retards the chemical reaction/diffusion.

Recently, flexible electrodes with biaxial/omnidirectional stretchability have attracted significant attention. However, most existing pliable electrode materials can be only stretched in one direction. In this work, an unexpected isotropic van der Waals (vdW) heterostructure is proposed, based on the assembly of two- dimensional crystals of anisotropic black phosphorene (BP) and transition metal carbide (TiC₂). Using vdW-corrected density functional theory calculations, the BP/TiC₂ vdW heterostructure was predicted to have excellent structural and mechanical stability, superior electrical conductivity, omnidirectional flexibility, and a high Li storage capacity. We have unraveled the physical origin of the excellent stability, as well as the Li adsorption preferences of the lithiated heterostructure, based on a three-step analysis of the stability of the Li-adsorption processes. In addition, the BP/TiC₂ vdW heterostructure can also be applied as the anode material for flexible Na-ion batteries because of its high Na storage capacity and strong Na binding. However, compared with Na adsorption, the capacity is higher, and the adsorption energy is more negative for Li adsorption. Our findings provide valuable insights into the exploration of a rich variety of vdW heterostructures for next-generation flexible energy storage devices.