Polyzwitterionic double-network hydrogel with high salt resistance and low evaporation enthalpy for efficient solar desalination and electricity generation

Abstract

Solar-driven interfacial evaporation has emerged as a sustainable and promising technology for addressing the freshwater scarcity and energy resource limitations. Nevertheless, its practical implementation is still constrained by salt deposition, high evaporation enthalpy and intermittent solar illumination. Herein, a facile preparation method is used to prepare a polyzwitterionic double network hydrogel-based solar steam generator. The inherent anti-polyelectrolyte effect of zwitterionic groups makes the hydrogel form a more hydrated polymer network in high-concentration brine, improving the evaporation performance. The interpenetrating network structure formed from chitosan and polyacrylic acid improves the mechanical properties. The evaporator possesses a higher evaporation rate of 2.26 kg m⁻² h⁻¹ and the lower evaporation enthalpy of 1019 J g⁻¹ in 10 wt% brine than that in pure water (evaporation rate: 2.08 kg m⁻² h⁻¹; evaporation enthalpy: 1128 J g⁻¹). The evaporator keeps a stable evaporation rate after 7 evaporation cycles and shows a long-term durability in outdoor evaporation experiments. Furthermore, the hydrogel evaporator is employed for temperature difference power generation and thermoelectric evaporation, generating a high output power density (181.25 mW m⁻² in wet state) under 1.0 sun and achieving an evaporation rate of 1.23 kg m⁻² h⁻¹ without solar illumination in 10 wt% brine. This study proposes a novel strategy to construct durable solar evaporators with high salt resistance and low evaporation enthalpy for efficient water production and electricity generation.