Physical hydrogel evaporators with uniformly dispersed hydrophobic components for freshwater and electricity cogeneration

Solar hydrogel evaporators are attracting increasing attention due to the growing scarcity of freshwater resources. EGaIn liquid metal (LM), known for its excellent photothermal conversion and electrical conductivity, holds promise for enhancing hydrogel evaporators. However, the poor dispersion and tendency to deposit in water limit the practical application of LM. To overcome this challenge, carboxylated multi-walled carbon nanotubes (CNT-COOH) and chitosan hydrochloride (HACC) are employed to uniformly diffuse and stabilise LM in this work, forming a stable suspension that can be used to prepare efficient hydrogel evaporators. A purely physical crosslinked hydrogel is then fabricated by carefully regulating intermolecular interactions. Since no chemical crosslinking agents are used, the risk of contaminating purified water through potential leakage is eliminated. This hydrogel evaporator exhibits excellent solar absorption (85 % across the 250–2500 nm wavelength range), a high evaporation efficiency of 91.2 %, and an evaporation rate of 2.50 kg m -2 h −1 under 1 kW m −2 irradiation. The ion concentrations in the purified water are reduced by three orders of magnitude, well below the WHO standard. Additionally, this gel evaporator also generates electricity, offering an approach to addressing both freshwater scarcity and clean energy needs simultaneously.