Nitrogen-Doped Unusually Superwetting, Thermally Insulating, and Elastic Graphene Aerogel for Efficient Solar Steam Generation

By removing the oxygen-containing functional groups, thermal treatment in inert gas has been widely reported to improve the hydrophobicity of carbon materials. However, this work reports a contrary phenomenon for the nitrogen-doped graphene aerogel (NGA). As the temperature of thermal treatment increases from 200 to 1000 degrees C, NGA becomes more and more hydrophilic and the superwetting property remains for weeks in air. To uncover this unusual phenomenon, the effect of nitrogen doping is studied through both experiment and MD simulations. The effects of air exposure and air humidity are further investigated in detail to illustrate the whole physical picture clearly. The superwetting behavior is attributed to the preferential adsorption of water molecules to the nitrogen-doped sites, which significantly inhibits airborne hydrocarbon adsorption. In combination with the excellent properties including mechanical elasticity, high light absorption, and good thermal insulation, an efficient photothermal and solar steam generation performance is demonstrated by using NGA-600 as the photothermal material, presenting a high energy conversion efficiency of 86.2% and good recycling stability.