Ion‐Transfer Engineering via Janus Hydrogels Enables Ultrahigh Performance and Salt‐Resistant Solar Desalination

Abstract

Emerging solar interfacial evaporation offers the most promising response to the severe freshwater crisis. However, the most challenging bottleneck is the conflict between resisting salt accumulation and maintaining high evaporation performance since conventional salt‐resistant evaporators enhance water flow to remove salt, leading to tremendous heat loss. Herein, an ion‐transfer engineering is proposed via a Janus ion‐selective hydrogel that enables ion‐electromigration salt removal, breaking the historical dependence on water convection, and significantly lowering the heat loss. The hydrogels drive cations downward and anions upward, away from the evaporation surfaces. An electrical potential is thus established inside the evaporator and salt in 15 wt% brine is removed stably for seven days. A record‐high evaporation rate of 6.86 kg m−2 h−1 in 15 wt% brine, 2.5 times the previously reported works, is achieved. With the from‐scratch salt‐resistant route, comprehensive water‐thermal analysis, and record‐high performance, this work holds great potential for the future salt‐resistant evaporators.

Ion engines in hydrogels boosting hydrovoltaic electricity generation

“…Notably, as the primary substrate, the hydrogel can provide a higher evaporation rate (Fig. 3c) than other materials, 50–53 contributing to electricity generation.…”

“…Notably, as the primary substrate, the hydrogel can provide a higher evaporation rate (Fig. 3c) than other materials, [50][51][52][53] contributing to electricity generation. Secondly, using carbon fibre in tandem with the high-water absorption capacity of hydrogels guarantees that the ion-engine HEG is filled with water (Fig.…”

Self‐Assembled Nanofibrous Hydrogels with Tunable Porous Network for Highly Efficient Solar Desalination in Strong Brine

“…To simulate the salt distribution in NHSEs, a mass flux of NaCl (J evap ) was applied on the desalination interface: [44] J evap = q ,, evap ⋅ c h evap 𝜌 (20) 𝜌 (c, T) = 𝜌 0 (T) + 𝛽 ⋅ c (21) where q ,, evap represents the evaporation heat flux on the surface, c is the brine concentration, h evap is the latent heat at the desalination interface, 𝜌 is the brine density, which is affected by the brine concentration and temperature, and 𝛽 (0.033 kg mol −1 ) is a proportionality constant. The salt concentration at the bottom of NHSEs was set as the 3.5%-20%.…”

“…[14,15] Salt accumulation in HSEs often occurs during continuous evaporation especially in strong brine, which compromises the photothermal evaporation process by blocking water transport and solar reception. [16][17][18][19] Existing strategies for enhancing salt tolerance in HSEs include local crystallization, [18,20] ion rejection, [17,21] Janus design, [19,22] and back diffusion. [23][24][25] Among these approaches, promoting back diffusion of ions into the bulk water is advantageous since it aims to eliminate salt accumulation in HSEs with feasible structures.…”

Carbonized CMPs Hollow Microspheres-Based Hydrogel Composite Membranes with a Hierarchical Architecture for Efficient Solar-Driven Interfacial Evaporation

“…Water scarcity poses a growing threat to sustainable economic development and social progress . Continued population growth, climate change, and environmental pollution have exacerbated the shortage of fresh water. , Desalination technology of brackish water and seawater has become a key to addressing the cascading negative effects of global shortage of fresh water. , However, as this technology becomes increasingly dependent on fossil fuels, there is a growing need to seek and integrate renewable energy sources, such as solar energy. , Solar-driven distillation of seawater is an eco-friendly strategy that has received much attention. , However, in practical applications, the traditional mode of volumetric heating always led to a large amount of heat loss due to the easy dispersion of natural light. , Therefore, solar-driven interfacial evaporation (SDIE), an advanced strategy which localizes the conversion process at the “gas–liquid interface” and thus avoids huge heat losses, has been widely used. − Owing to the thermal-collection capability of the interface of SDIE being always dependent on the physical properties of evaporators, extensive efforts have been dedicated to designing ideal photothermal materials, including plasmonic metal nanoparticles, ,− semiconductors, − polymers, − carbon-based materials , and hydrogels, etc. , …”