A Molecularly Engineered Zwitterionic Hydrogel with Strengthened Anti-Polyelectrolyte Effect: from High-Rate Solar Desalination to Efficient Electricity Generation

Polyzwitterionic hydrogel is an emerging material for solar-driven water evaporation in saline environment due to its special anti-polyelectrolyte effect, which is a promising approach to co-generation of freshwater and electricity. However, the molecular impact on anti-polyelectrolyte effect remains unclear, let alone to optimize the zwitterionic structure to promote water evaporation efficiency in high-salinity brine. Herein, a molecularly engineered zwitterionic hydrogel is developed and the incorporated phenyl-methylene-imidazole motif greatly enhances the salt binding ability and strengthens anti-polyelectrolyte effect, leading to boosted hydration, improved salt tolerance, ultra-low evaporation enthalpy (almost half of traditional zwitterionic gel), and durable anti-microbial ability in brine. Besides, gradient solar-thermal network is penetrated to optimize water transport channel and heat confinement. The gel exhibits excellent evaporation rate of 3.17 kg m ⁻² h ⁻¹ in seawater, which is 1.6 times of that in water and such high efficiency could be maintained during 8 h continuous desalination, demonstrating outstanding salt tolerance. The high flux of ion stream can generate considerable voltage (321.3 mV) simultaneously. This work will bring new insights to the understanding of anti-polyelectrolyte effect at molecular level and promote materials design for saline water evaporation.