An effective material for solar steam generation applications: Gradient graphene sponge

The efficient use of solar energy for clean water is a renewable and environmentally-friendly route to solve global water scarcity. For this, we report the preparation of light, mechanically durable, and effective photothermal material. A simple acid impregnation method was applied to graphene sponge material (GSM) possessing hydrophobic character to gain partial hydrophilicity to obtain a gradient structure. The morphological and structural properties of the gradient graphene sponge material (GGSM) were carried out using scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray powder diffraction patterns, Fouriertransformed infrared spectroscopy, and water drop contact angle measurements. GGSM showed fast and effective water vapor conversion performance due to the gradient structure, as well as the high rate of sunlight absorption and photothermal conversion thanks to graphene. With the advantageous feature of gradient structure, GGSM achieved a high water vapor conversion capacity (1.79 kg/m2h) and solar thermal efficiency of 57% compared to GSM (1.58 kg/m2h; 45%). This new material provides a novel approach to solar energy applications.