# Hydrogel‐Coated Foam Evaporator Achieving Four‐In‐One Benefits for Efficient and Stable Solar‐Driven Water Purification

## TL;DR

A new foam-based solar evaporator with a hydrogel coating improves water purification by reducing energy use and enhancing stability.

## Contribution

A universal strategy for foam-based solar evaporators using hydrogels to address multiple challenges in one approach.

## Key findings

- The hydrogel-coated foam evaporator achieved a 62% improvement in evaporation performance for melamine foam.
- The FCH evaporator reached an evaporation rate of 7.93 ± 0.37 kg m−2 h−1 under 1 sun irradiation.
- The evaporator maintained high performance over 30 days of continuous seawater testing.

## Abstract

Interfacial solar evaporation has emerged as an innovative water purification strategy due to its environmental friendliness, high efficiency, adaptability to various water sources. This study introduces a universal strategy for foam‐based solar evaporators, leveraging unique advantages of hydrogel materials to effectively reduce evaporation enthalpy. At the same time, it addresses challenges such as the need for pore formation in hydrogels, water‐induced swelling, and the detachment of photothermal materials, achieving “four benefits in one approach.” The fabrication process takes only 40 min and features an extremely low carbon footprint (0.00462 kg CO2 eq kg−1). After modification, the evaporation performance of different foam‐based evaporators improved by 15%62%, with the melamine foam‐based evaporator showing the most notable enhancement (62%). Using melamine foam as the supporting material, a PVA‐melamine foam composite hydrogel evaporator (FCH) is successfully fabricated via the hydrogel‐based improvement technique. FCH evaporator achieved an exceptional evaporation rate of 7.93 ± 0.37 kg m−2 h−1 under 1 sun irradiation and maintained excellent stability during 30‐day continuous seawater test. Owing to the superior stability of the hydrogel thin layer, FCH evaporator retained high evaporation performance even under extreme conditions. This study provides new insights and practical solutions for advancing sustainable water purification technologies.

This study introduces a universal strategy for foam‐based solar evaporators, leveraging the unique advantages of hydrogel materials to effectively reduce evaporation enthalpy. At the same time, it addresses challenges such as the need for pore formation in hydrogels, water‐induced swelling, and the detachment of photothermal materials, achieving “four benefits in one approach.”