Fermat Spiral‐Engineered Thermoresponsive Hydrogel Evaporator Arrays: Breaking the Efficiency‐Stability Trade‐Off for All‐Day‐Round Solar‐Driven Water Production

ABSTRACT Constructing 3D hydrogel evaporator has emerged as a promising strategy to increase the evaporation surface area in solar‐driven water production systems. However, their practical application suffers from the trade‐off between overall efficiency and structural stability. Herein, a 3D Fermat‐spiral‐arranged cylindrical evaporator arrays (FSAE) is developed by combining Au‐decorated black phosphorus (Au/BP) as localized surface plasmon resonance (LSPR)‐enhanced light absorbers and hydrophilic calcium silicate hydrate (CSH)‐modified hydroxypropyl cellulose (HPC) as thermo‐responsive networks. According to finite element simulations, the Fermat‐spiral architecture optimizes space utilization and minimizes inter‐unit shading, enabling high‐efficient solar harvesting across different incident angles. Computed tomography and confocal microscopy reveal that the microchannels can be dynamically regulated via thermoresponsive HPC‐triggered hydrogen bonding rearrangement. Consequently, FSAE exhibits a remarkable evaporation rate of 3.92 kg m −2 h −1 under one sun illumination. Outdoor tests validate the all‐day‐round performance of steady water production (∼25.7 L m −2 day −1 ) and power generation (619.5 mV open‐circuit voltage) over continuous desalination, with capabilities to desalinate 20 wt.% brine, remove heavy metals/organic dyes, and support wheat cultivation with purified water. This work provides a viable route to surmount the trade‐off between the evaporation efficiency and stability during prolonged practical applications, offering a paradigm for high‐performance solar‐driven water production.