Defect- and Composite-Engineered Free-Standing Nanoporous Graphene Film for High-Efficiency Solar-Driven Water Evaporation

Solar-driven interfacial evaporation has emerged as a promising strategy for sustainable freshwater production. However, simultaneously achieving efficient photothermal conversion and optimized water transport within a single material system remains challenging. Herein, three-dimensional (3D) nitrogen-doped nanoporous graphene (NG) with tunable microstructures is synthesized by tuning the composition of Ni-based nanoporous templates via chemical vapor deposition (CVD). The defect density of the CVD-grown NG clearly increases with the number of components (or entropy) of the nanoporous alloys, reducing thermal conductivity, and promoting heat localization. Furthermore, when Mo element is included in the nanoporous alloy template (np-MnNiCoFeMo), MoC forms during CVD, inducing secondary nanoholes on the graphene tube walls and creating more defects. By selectively removing the alloy template, the obtained nanoporous graphene/MoC composite (5-NG@MoC) exhibits synergistically enhanced photothermal conversion due to the combined light absorption from both components of the composite. Consequently, 5-NG@MoC achieves a broadband solar absorption of 94% (250-2500 nm) and delivers an evaporation rate of 1.76 kg·m-2·h-1 with a photothermal conversion efficiency of 92.8% under one-sun irradiation. The free-standing and ultralight composite also demonstrates excellent stability and salt resistance during seawater desalination. This work provides an effective strategy for engineering graphene-based photothermal materials toward high-efficiency water evaporation.