Gradient Vertical Channels within Aerogels Based on N-Doped Graphene Meshes toward Efficient and Salt-Resistant Solar Evaporation

In the drive toward energy harvesting, graphene and their derivations are the most promising photothermal materials for solar evaporation. Here is a facile approach for constructing gradient vertical channels within a ring-like three-dimensional (3D) aerogel based on porous N-doped reduced graphene oxide (N-RGO) meshes toward interfacial water evaporation. Intriguing gradient microchannels are constructed by introducing a concentration gradient of NH4OH (as antifreeze) within the N-RGO hydrogel before traditional freeze-drying. Based on both theoretical simulation and experimental demonstrations, aerogels with ring-like photothermal structures harvest light without angle dependence and exhibit ring-by-ring thermal insulation and high photothermal conversion efficiency (74.8%). Moreover, unique 3D gradient vertical microchannels concentrate water into hot regions and achieve effective interfacial evaporation, leading to a high evaporation rate (2.53 kg·m–2·h–1, normalized to the evaporation area including both the top and side surface) and solar-to-vapor conversion efficiency (90.3% and 41% higher than that of honeycomb-like aerogels). Besides, the controllable N-doping in terms of concentration and configurations (i.e., pyridinic and graphitic N-dopants) greatly enhances the water transport and evaporation. The aerogel exhibits salt resistance in highly concentrated saline water under 5 h of cycling and also shows structural stability under the corrosive liquid and external mechanical compression. Our work provides attractive ways of constructing the 3D gradient ordered microstructures by assembling graphene meshes and achieving effective thermal management and interfacial water evaporation.