Ultralight Biomass Porous Foam with Aligned Hierarchical Channels as Salt-Resistant Solar Steam Generators

The creation of solar steam generators with both high energy conversion efficiency and desired salt-resistant performance is essential for practical desalination. Herein, we report for the first time the fabrication of polypyrrole-coated biomass porous foam as efficient solar steam generators. The as-prepared foams possess a low thermal conductivity of 0.022 W M–1 K–1 for alkali-treated corn straw (CSA) and 0.027 W M–1 K–1 for both microwave- and alkali-treated corn straw (CSMA). Based on their high light absorption (95–100%), superhydrophilic wettability, excellent thermal insulation, and unique aligned channels, the foams show excellent energy conversion efficiency of 89.74, 91.08, and 91.54% for the polypyrrole-coated CSA (P-CSA) and 96.8, 97.05, and 98.32% for the polypyrrole coated CSMA (P-CSMA) at light intensities of 1, 2, and 3 kW m–2, respectively. Importantly, thanks to their aligned hierarchical channels, our generators show extraordinary salt-resistant performance, e.g., the energy conversion efficiencies of P-CSA and P-CSMA were measured to be 62.30 and 94.7% in 20 wt % NaCl at 1 kW m–2 irradiation, respectively. Furthermore, no obvious salt accumulation was observed after 30 d of continuous operation at real sunlight irradiation, implying an outstanding long-term stability for practical solar steam generation.