Ion Permeation in Zwitterionic Hydrogel for Stable Solar Desalination and Power Generation

Interfacial solar evaporation holds promise for desalination but suffers from salt accumulation and unutilized salinity-gradient energy. Conventional salt-rejection strategies largely rely on passive diffusion, which is frequently compromised under high salinity. Here, we propose an ion permeation strategy using a zwitterionic hydrogel evaporator. The charge-balanced hydrogel network enables downward ion permeation while suppressing upward water convection, thereby preventing interfacial crystallization. As a proof-of-concept, a zwitterionic hydrogel evaporator featuring spatially separated channels for brine convection and ion permeation was engineered. It sustained high evaporation rates over 3.50 kg m^-2 h^-1 across 0-25 wt.% brines and showed no salt accumulation after 105 h of continuous desalination in 3.5 wt.% brine. Spectroscopy and simulations validated the ion permeation mechanism. Furthermore, the resulting salinity gradient was leveraged for power generation, delivering a record-high power output of 24 W m^-2. This work presents a stable ion permeation-regulated paradigm for synergistic brine resource and solar energy utilization.