Janus monolithic thermal management via directional radiative cooling and heat dissipation

The surging heat from urban infrastructures calls for energy-efficient thermal management beyond electricity-intensive cooling. Here we realize directional heat conduction and emission using a Janus monolith composed of hierarchical melamine and chitosan anisotropic frameworks with crisscross channels formed by multidirectional ice-templating. Integrating silica microspheres enables effective interfacial radiative cooling, while liquid metal is selectively coupled into the basal chitosan channel walls to build lateral thermal pathways, boosting the local thermal conductivity by > 200-fold from 0.1 to 22.5 W m−1 K−1. The apical domain preserves radiative cooling and suppresses heat backflow over 10,000 cycles. With crisscross engineering, the Janus monolith exhibits all-day passive cooling capability, delivering a daytime net cooling power of 47.3 W m−2 and a nighttime net cooling power of 64.8 W m−2, while achieving a temperature reduction exceeding 5 °C under solar irradiation. In outdoor tests, it lowers the temperature of a sun-exposed metal surface by up to 29 °C and enables all-day sub-ambient regulation in a building-simulation setup, maintaining the indoor temperature >4 °C below ambient. Both mechanical properties and cooling performance retain >90% of their initial values after 30 days of outdoor exposure. Field tests on air conditioners and electric vehicles further show up to 23.0% energy savings, highlighting the promise of this low-cost bifunctional Janus architecture for adaptive building thermal management.