Cellulose-based hydrogel simultaneously possessing solar and evaporative cooling performances for energy-saving window and personal thermal management.

Thermochromic smart windows have been widely developed for building energy saving. However, most smart windows suffer from limited energy-saving performance, fixed phase transition temperature, and are not suitable for the temperature regulation needs of different application scenarios. Herein, a unique self-adaptive thermochromic hydrogel (HBPEC-PNA) with self-moisture-absorbing performance is reported that assembles solar energy cooling and evaporative heat dissipation. Importantly, the hydrogel shows excellent energy-saving performance by using the synergistic interaction of solar and evaporative cooling. The HBPEC-PNA hydrogel has an adjustable critical transition temperature (21.8-33.9 °C), a high solar modulation (ΔT = 78.90 %), and a high light transmittance (T = 90.15 %). Interestingly, the hydrogel harvests water molecules from the surrounding air, enabling it to be directly used in circumstances without losing its ability to dynamically regulate solar energy transmission due to water loss. Furthermore, the indoor simulation experiments confirmed that the dual-cooling system can reduce 14.2 and 2.4 °C, respectively, compared to ordinary glass and conventional smart window. Dramatically, HBPEC-PNA hydrogel can be utilized to personal thermal management due to its superior cooling property. This work provides an attractive strategy that will contribute to the development of thermochromic materials with excellent temperature regulation ability.