Gradient Pore Engineering of MXene-Based Foam Evaporators for Efficient Solar Interfacial Evaporation and Evaporation-Induced Electricity Generation

Abstract Solar-driven interfacial evaporation coupled with evaporation-induced electricity generation offers a promising route for simultaneous freshwater production and low-grade energy harvesting, but its performance is often limited by the trade-off among water transport, heat localization, and ion migration. Here, an MXene-based porous foam evaporator with coupled pore-size and wettability gradients was fabricated through prefreezing and freeze-drying. The resulting architecture comprised a small-pore upper layer, an interconnected middle layer, and a large-pore bottom layer, enabling localized heating, continuous capillary water supply, rapid vapor escape, and directional ion transport. Benefiting from the broadband photothermal response of MXene and the hydrophilic PAAm-SA network, the optimized evaporator achieved solar absorptance above 90% and an evaporation rate of 1.44 kg m–2 h–1 under one sun, and an equivalent evaporation enthalpy of approximately 1.43 kJ g–1. After 100 h, 94.4% of the initial evaporation rate was retained. The device also exhibited stable electrical output, with voltage and current retentions of 93.4% and 90.1%, respectively. This work provides a simple strategy for integrating solar-driven interfacial evaporation and evaporation-induced electricity generation.