Sustainable heat harvesting via thermal nonlinearity

Converting the pervasive low-grade environmental waste heat of approximately 200 EJ globally per year (equivalent to 27 Gt of CO₂ emission) into electricity promises energy sustainability and would contribute to carbon neutrality. Heat harvesting technologies capture this waste heat through thermodynamic heat engines across various working media. Conventional heat harvesting approaches have primarily focused on limited incremental improvements in thermophysical output. However, advances in thermal nonlinearity and material anisotropy offer substantial gains but are often overlooked. In this Perspective, we delve into the role of intrinsic thermal nonlinearity with multiscale physical understanding to transform heat or thermal energy harvesting technologies from linear to nonlinear processes.