Simultaneous solar steam and electricity generation from biochar based photothermal membranes

Abstract

Clean water and energy are essential for reducing poverty, fostering economic growth and sustainable development while mitigating CO2 emissions. Considering that, solar-powered interfacial vapor or steam generation is sustainable and promising environmental technology for both water purification and energy generation while being CO2-free. Despite continuous research progress, most of the solar absorbers to capture sunlight following heat conversion for steam generation are generally made from expensive nanostructures, which in part prevents their widespread manufacturing for useful applications. Herein, we experimentally demonstrate a biomass-derived carbon composite membrane that nearly covers the entire sunlight spectrum as a solar absorber with an estimated absorptivity of 90%. As a result, the light absorbed yields a surface temperature of 55 °C at the surface of the B700 and 33 °C for water. Evaporation rates up to 1.26 and 1.16 kg/(m2 h) and solar-to-vapor efficiencies of 80 and 74% were recorded in presence of sodium chloride with two different types of biochar B700 and B300 based photothermal membranes, respectively, under 1 sun illumination. The water evaporation in presence of mixed sodium chloride/magnesium chloride reached up to 1.21 and 1.05 kg/(m2 h) with 77 and 69% efficiency with B700 and B300; due to different solar absorber geometry. Furthermore, by merging the thermoelectric technology, we exploit the concept of hybrid clean water and energy generation. At a relative humidity of 60%, the thermoelectric device may generate approximately 0.9 W/m2 power density. These results highlight the interactive effects of biochar and polyvinylidene fluoride with porous hierarchies and enhanced absorption of sunlight, thus enabling a considerable elevation of temperature with great potential for clean water and energy. Overall biochar photothermal membrane represents a significant advancement as low-cost sustainable technology, addressing both water and energy challenges by providing efficient, environmentally friendly solution for freshwater production and clean power generation.