Nitrogen-Doped Graphene Aerogel toward Efficient Solar Steam Generation: Synergistic Effects of Thermal Conductivity and Wettability

Abstract

Solar-driven interfacial evaporation technology is regarded as a promising strategy for global freshwater shortage owing to its green and sustainable desalination process. Graphene aerogel (GA) is widely utilized in the design of solar-driven steam generation systems due to its excellent photothermal conversion efficiency and broad spectral absorption. Given the significant impact of hydrophilicity and thermal insulation on the performance of evaporators, nitrogen doping in the graphene structure not only effectively enhances its wettability but also allows for moderate tuning of its thermal conductivity, thereby optimizing the overall performance of the evaporator. Therefore, graphene oxide (GO) and ethylenediamine were used to prepare nitrogen-doped graphene aerogel (NGA) via a one-step hydrothermal method. Experimental investigations and molecular dynamics (MD) simulations were employed to explore the effects of varying nitrogen-doping concentrations on the thermal conductivity and wettability of NGA. The results revealed that as the nitrogen-doping concentration increased, the aerogel exhibited enhanced wettability, while the thermal conductivity initially decreased and then increased. This phenomenon is attributed to the fact that improved wettability can hinder heat convection, resulting in reduced heat transfer efficiency. However, further enhancement in wettability reduces the solid–liquid interfacial thermal resistance, thereby boosting heat transfer performance. Consequently, NGA-2, with an optimal nitrogen-doping concentration, demonstrated superior evaporation performance, achieving a high evaporation rate of 1.64 kg m^–2 h^–1 and an outstanding evaporation efficiency of 92.2% under one-sun irradiation. This study highlights the improved performance of solar evaporators through the synergistic effects of heat and mass transfer, underscoring their significant potential in seawater desalination applications.