Sunflower-inspired smart evaporator with omnidirectional solar tracking for highly enhanced energy-capturing and sustainable freshwater harvesting

Efficient solar energy utilization and stability are critical for the developed field operation of interfacial solar vapor generation. Inspired by natural sunflowers, we developed an advanced biomimetic phototropic solar interfacial evaporator (BPSIE) capable of omnidirectional light tracking and efficient solar energy harvesting without any electronics. The stem of BPSIE is comprised of a stimuli-responsive hydrogel that detects incident light and moves in any direction in 3D space using embedded negative feedback control. The BPSIE maintains a high level of light-to-vapor energy conversion efficiency of 99.27 % and a water evaporation rate reaching 6.18 kg m^-2 h⁻¹ under 4 simulated solar irradiations due to its phototropism at incidence angles from 0° to 180°, enhancing energy harvest by 200 % compared to non-tropistic materials, which is confirmed by simulations of time-dependent volume shrinkage and temperature distribution. Different from other phototropic solar evaporators, our developed BPSIE is highly porous and mechanically strong and thus can hold itself in air. With only its stem immersed, the porous structure exhibits fast water transport from the water surface to evaporating disk. Additionally, the BPSIE is capable of fast self-healing if severely broken, providing additional stability and enabling sustainable field operation in the real world.