Thermally Chargeable Supercapacitor with 3D Ti3C2Tx MXene Hollow Sphere Based Freestanding Electrodes

Abstract Thermally chargeable supercapacitors (TCSCs) are emerging and promising devices that could convert thermal energy spontaneously existing in nature into electricity and then store energy for further utilization. Herein, this work reports on the freestanding 3D Ti 3 C 2 T x MXene‐based TCSC, where lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), poly(ethylene oxide) (PEO), and polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP) serve as gel electrolyte. Different from the semiconductor‐based thermoelectric materials, the fabricated Ti 3 C 2 T x TCSC exhibits a high Seebeck coefficient of 78.4 mV K −1 . Moreover, when applying a temperature difference (ΔT) of 5.8 K between the cold and hot sides, the Ti 3 C 2 T x TCSC devices provide a stable high voltage of 400.6 mV. The charging/discharging cycles of the Ti 3 C 2 T x TCSC devices upon periodic Δ T of 3.3 and 5.8 K demonstrate their excellent stability. To realize the practical application, the four Ti 3 C 2 T x TCSCs devices connected in series are charged by supplying a Δ T of 5.8 K and used to power a digital timer, demonstrating the possibility and application of the TCSCs in self‐powered integrated electronics.