3D Cellulose‐Based Solar Evaporator with Tunable Porous Structures for High Steam Generation

Solar vapor evaporation have emerged as a promising green technology to harvest fresh water. Achieving high evaporation rates while employing accessible and renewable materials is key focus in this field. Here, a 3D cylindrical‐shaped solar evaporator composed of natural cellulose is fabricated through ice‐templating freezing combined with crosslinking gelation. It demonstrates an evaporation rate of 4.2 kg m −2 h −1 under 1 sun irradiation, and reaches an energy efficiency of 173%, surpassing most reported cellulose/wood‐based evaporators. This enhanced performance is facilitated by absorbing energy from surrounding, possessing connected pores, and reducing the evaporation enthalpy. Moreover, a systematic exploration of the correlation between pore size and evaporation performance reveals that the reduced pore size (several micrometers) does not necessarily result in a higher evaporation rate, despite improving the fluid transportation. The interaction between water and cellulose induces the formation of intermediate water and reduces the evaporation enthalpy by more than 35%. Thus, the final evaporation performance is determined by a synergistic effect involving water transport, hydrophilicity, and vaporization enthalpy. Giving the high evaporation rate achieved, this 3D cellulose‐based solar evaporator presents a promising candidate toward a high‐throughput, eco‐friendly solar steam generation devices, aligning well with the criteria of green and sustainable development.