Constructing a Thin Layer of the Concentrated Polyelectrolyte Solution on the Hydrogel Surface That Can Considerably Improve the Solar Evaporation Efficiency

Converting solar energy to evaporative energy to obtain clean water has been intensively studied. However, the efficiency of the reported solar evaporators remains limited, and their construction is complex and challenging to control. Here, we report a facile method for constructing efficient solar evaporators by utilizing a thin-layer, highly concentrated polyelectrolyte solution as the evaporation layer. Under an electric field, a single layer of polyelectrolyte–shelled micelles is grafted onto a hydrogel surface, controllably and stably modifying highly concentrated polyelectrolyte chains on the outermost surface. These chains, with their low chemical potential, efficiently absorb water to form the evaporation layer. Theoretical calculations indicate that the water molecules in the evaporation layer possess high energy as the hydrogen bonds between them are significantly disrupted, thus minimizing the evaporation energy. Consequently, for simulated seawater and under 1 kW m^–2 irradiation, the as-prepared evaporator without a photothermal component achieves a high evaporation rate of 3.74 kg m^–2 h^–1 (1.5 times the highest nonphotothermal hydrogels) and that with photothermal particles β-Ti₃O₅ reaches a record-breaking value (6.92 kg m^–2 h^–1). Remarkably, the ion rejection ratio is as high as 99.97% due to repulsion from the positively charged polyelectrolyte.