Emerging 2D MXene Materials for Flexible Thermoelectric Energy Harvesting

The pursuit of energy-efficient technologies is crucial for achieving sustainability amid rising global energy demands and climate concerns. MXenes-a class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides-have recently attracted significant attention in thermoelectric (TE) research due to their outstanding electrical conductivity, tunable surface chemistry, and unique layered structures. This review uniquely focuses on the integration of MXenes into flexible and wearable platforms, offering a systematic analysis of material innovations specifically tailored to mechanical compliance. Beyond material-level transport properties, we critically evaluate actual device-level demonstrations, including fabrication strategies for flexible TE generators (f-TEGs), that achieve impressive outputs, such as Seebeck voltages of up to 399.9 mV for 200 p-n modules. To assist readers in gauging progress, we provide a comprehensive comparative analysis of diverse MXene architectures, summarized in a quantitative benchmark table covering Seebeck coefficients (S), electrical conductivity (σ), power factor (PF), and ZT values. Notably, experimental optimization has led to performance breakthroughs, with MXene-based flexible films exhibiting power factors exceeding 2100 µW m^-1 K^-2 and ZT values as high as 1.33 at room temperature. Finally, critical challenges, including environmental stability and large-scale manufacturing, are discussed alongside future perspectives on multifunctional MXene systems.