Hydrogel-Enabled Interfacial Water Regulation for Enhanced Multistage Solar Evaporation

Solar-driven interfacial evaporation offers an ecofriendly and sustainable route for clean water production, but its performance is fundamentally limited by the energy input and conversion efficiency of single-stage systems. Hydrogel-based materials have demonstrated advantages in regulating water existing and interfacial properties in single-stage evaporation systems. However, their integration with multistage evaporation architectures has not been systematically explored. In response, we used bacterial cellulose (BC) gel as a model material, constructing a cascade multistage solar evaporation unit (CSU) that features latent heat recovery, effective thermal localization, and confined interfacial environments that modulate water states. This design accelerates vapor generation and enhances overall energy utilization. The 4-stage CSU achieves a high water production rate of 2.01 kg m⁻² h⁻¹ under 1 sun. Outdoor experiments confirm stable operation under fluctuating conditions and high-quality water production meeting drinking standards. In conclusion, this work provides a general strategy for coupling interfacial water regulation with multistage evaporation architecture, advancing high-efficiency solar desalination technologies. © 2026 The Author(s). Small Structures published by Wiley-VCH GmbH.