Design of Hydrogels with Dual Asymmetric Structures for Solar-Driven Water Evaporation and Evaporation-Induced Power Generation

The global challenges of freshwater scarcity and sustainable energy demand drive the development of integrated systems capable of concurrent solar desalination and electricity generation. We present a dual-asymmetric PVA/cellulose/CNT composite hydrogel synthesized via Pickering emulsion templating and freeze–thaw cycling. This design constructs a gradient porous network with continuous wettability and charge-density gradients by using CNF and CMC as structural and physicochemical modifiers. The dual asymmetry arises from the gradient porous architecture stabilized by CNF and CMC emulsions, as well as the continuous wettability and charge gradient derived from differing hydrophilicity and zeta potential between CNF and CMC. The incorporated CNTs act as efficient photothermal conversion agents, giving the hydrogel a broadband solar absorption efficiency of ∼98%. Under 1-sun irradiation, the optimized hydrogel achieves an evaporation rate of 1.21 kg m–2 h–1 for tap water and 0.95 kg m–2 h–1 for 3.5 wt % NaCl solution, while generating an open-circuit voltage up to 440 mV in saline and 470 mV in acidic solutions. The dual-asymmetric structure significantly enhances hydrovoltaic output by synergistically regulating ion transport and charge accumulation. This work provides a rational design for multifunctional hydrogel evaporators, offering a sustainable route for decentralized water and energy co-generation.