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), respectively. 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 polypyrrole coated CSA (P-CSA) and 96.8%, 97.05% and 98.32% for polypyrrole coated CSMA (P-CSMA) at light intensities of 1 kW m-2, 2 kW m-2 and 3 kW m-2, respectively. Importantly, thanks to their aligned hierarchical channels, our generators show extraordinarily salt-resistant performance, e.g. the energy conversion efficiency of P-CSA and P-CSMA were measured to be 62.30% and 94.7% in 20 wt% NaCl solution at 1 kW m-2 irradiation, respectively. Furthermore, no obvious salt accumulation was observed after 30 d continuous operation at real sunlight irradiation, implying an outstanding long-term stability for practical solar steam generation.