Alcogel-Based Interfacial Evaporation for Vertical Thermal Diode-Structured Smart Walls with Radiant Cooling

Traditional building envelopes with constant thermophysical properties constrain their capabilities in temperature regulation. Whether it is possible to achieve single-direction heat transfer along building envelopes with climate-adaptative thermophysical properties to enhance passive heat gain in winter and thermal dissipation in summer? In this work, through the capillary effect in interfacial evaporation and thermal diode structure, single-direction heat transfer with passively adjustable thermal properties in a vertical building envelope is practically achieved. An evaporation-condensation-based smart wall (ECSW) is manufactured for spontaneous and continuous cooling/heating supply to the built environment. The ECSW features climate-adaptative heat transfer characteristics with heat transfer coefficient transiting from 3.33 to ≈30 W m^-2 K^-1. Additionally, coupling with radiant cooling and photothermal capabilities, ECSW shows excellent thermal performances, i.e., a heat transfer at 5.44 W m^-2 by radiant cooling with a 5 °C cooler surface, and a heat transfer at 387.68 W m^-2 under solar illumination at 1000 W m^-2. Simulation results show that the ECSW enables building energy savings at 66.47% in Kunming. This study first reports vertical thermal diode building envelopes utilizing natural heating/cooling sources through interfacial evaporation for passive temperature regulation with low costs, performance stability and energy-saving potentials for smart and sustainable buildings.