Tunable Water Delivery in Carbon-Coated Fabrics for High-Efficiency Solar Vapor Generation

Solar vapor generation by localized heating and evaporation has potential to be a viable and "green" way to produce fresh water. This work reports a carbon black-coated cotton fabric with a tunable water delivery property for high-efficiency solar vapor generation under 1 sun. The fabric is prepared by an electrospray of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) on one-side of the fabric followed by dip-coating of the fabric with carbon black as a photothermal absorber. Depending on the duration of electrospray, the roughness gradient generated by the PVDF-HFP layer in the fabric leads to guided and continuous one-way water transport from the electrosprayed hydrophobic side to the hydrophilic side with a tunable delivery rate. The tunable water delivery capability of the fabric regulates the amount of water supplied to the vicinity of the photothermal absorber. Additionally, the fabric shows excellent broadband absorption and low thermal conductivity. In comparison with the carbon black-coated fabric without a roughness gradient, the regulation of water improves the solar vapor conversion efficiency, owing to reduced heat loss and better heat allocation. Under optimal conditions, a solar vapor conversion efficiency of 88.9% and a stable water evaporation rate of 1.33 kg (m²·h)^-1 under 1 sun are achieved.