| Summary: | On-face electronics (On-faceE) are urged to sense “anytime, anywhere” for enabling human senses to globally dominate the Internet of Things. However, with the limited lifetime of batteries and the miniaturization of the On-faceE, On-faceE are confronting two challenges: sustainable operation at the temperature (T) < 0 °C and frost/ice accretion security hazard. Of note, the face and On-faceE themselves continuously generate heat and are more reliable than solar-/motion-based heat supplies. However, such self-generated heat often occurs as waste heat, lost into the environment. Here, a film pioneering the intelligent conservation and utilization of this waste self-generated heat for enabling On-faceE to work even at -30 °C for 8 h is developed, through making a versatile cellulose hydrogel and enabling the super-hygroscopic gel to capture moisture at the T < 0 °C. It creates a ΔT up to 60 °C between inside T and ambient T (-30 °C) after sealing On-faceE and, importantly, intelligently stops conserving heat when the working T > 30 °C and demonstrates outstanding heat-conserving stability and sustainability, thus solving the two challenges without the expense of energy for heating and positioning it as an energy-saving “smart” T-regulating candidate. This work could address the energy shortage and heating costs for conquering low-T limitations for globalizing On-faceE.
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