Three-dimensional hierarchical oxygen vacancy-rich WO₃-decorated Ni foam evaporator for high-efficiency solar-driven...

Solar steam generation is considered to be an effective strategy to alleviate the global water shortage problem. Therefore, exploring highly efficient and thermal stability photothermal conversion materials is highly essential and urgent. In this work, we develop a three-dimensional (3D) oxygen vacancy-rich WO₃ with ''nanorod array grown on nanosheet array" unique architecture decorated on Ni foam (denoted as WO_3-x/NF) through a simple and effective hydrothermal method followed by an annealing route, which is applied as light-absorbing material. The 3D hierarchical porous unique structure of the WO_3-x/NF evaporator can supply a channel steam escaping and enhance the light trapping due to the multi-scattering effect, and the localized surface plasmon resonance (LSPR) effects of WO_3-x also contribute to increase the light absorption in the full solar spectrum. The as-prepared WO_3-x/NF evaporator reveals a high solar absorption (95%), an evaporation rate of 1.50 kg m^-2 h^-1 under one sun illumination, and a light-to-heat conversion efficiency of about 88%, as well as stable salt-resistance performance. The water purification results show that WO_3-x/NF evaporator has a significant effect on seawater desalination without significant salt accumulation and purification of heavy metal wastewater. Furthermore, the first-principles calculations reveal that WO₃ with oxygen vacancies has a narrower bandgap, which is more conducive to absorb solar energy from the whole spectrum. This work can provide a new avenue toward the design of other high photothermal conversion system.