Humidity-thermoelectric bimodal energy harvester for sustainable power generation

Thermoelectricity is a promising solution to utilize waste heat for electrical energy, whereas thermal saturation or the temporal absence of thermal gradient incurs discontinuities in energy harvesting. Meanwhile, utilizing humidity has recently emerged as an energy harvesting stimulus owing to its sustainable availability, but its low power output limits feasibility. Herein, we report a humidity-thermoelectric bimodal energy harvester (HT-BET) for sustainable and complementary power generation. Aqueous and air electrothermal wave (ETW) uniformly deposits palladium nitrate precursors and directly fabricates tunable palladium/palladium oxide/carbon-based composites (Pd/Pd_xO_y @C) in terms of morphology, composition, and interfacial characteristics, thereby screening optimal electrochemical electrodes for humidity-driven energy-harvesting cells. An asymmetric cell incorporating a solidified poly(4-styrenesulfonic acid) (PSSH) between screened Pd/Pd_xO_y @C and carbon fibers is integrated with a thermoelectric p–n junction employing Bi₂Te₃ cells to complete the HT-BEH fabrication. The single HT-BEH exhibits highly improved output power by 67 times (0.3 µW), compared with a thermoelectric cell (4.5 nW) at 308.15 K (∆T = 10.35 K) and 30% relative humidity (RH). Furthermore, the flexible multi-array of HT-BEHs achieves 0.41 µW output power for 16 h through the human skin temperature, sweat, and surrounding RH, thereby confirming the capability of sustainable energy sources for wearable platforms in ambient environments.