Facile Designed Manganese Oxide/Biochar for Efficient Salinity Gradient Energy Recovery in Concentration Flow Cells...

Development of effective, environmentally friendly, facile large-scale processing, and low-cost materials is critical for renewable energy production. Here, MnO/biochar composites were synthesized by a simple pyrolysis method and showed high performance for salinity gradient (SG) energy harvest in concentration flow cells (CFCs). The peak power density of CFCs with MnO/biochar electrodes was up to 5.67 W m^-2 (ave. = 0.91 W m^-2) and stabilized for 500 cycles when using 1 and 30 g L^-1 NaCl, which was attributed to their high specific capacitances and low electrode resistances. This power output was higher than all other reported MnO₂ electrodes for SG energy harvest due to the synergistic effects between MnO and biochar. When using a mixture with a molar fraction of 90% NaCl and 10% KCl (or Na₂SO₄, MgCl₂, MgSO₄, and CaCl₂) in both feed solutions, the peak power density decreased by 2.3-40.1% compared to 100% NaCl solution with Ca²⁺ and Mg²⁺ showing the most pronounced negative effects. Our results demonstrated that the facile designed MnO/biochar composite can be used for efficient SG energy recovery in CFCs with good stability, low cost, and less environmental impacts. When using natural waters as the feed solutions, pretreatment would be needed.