Innovative Energy Harvesting from Salinity Gradients: Asymmetric Flow-Electrode Capacitive Mixing with MnO Coated Activated Carbon

Salinity gradient power represents a promising source of renewable energy, and flow-electrode capacitive mixing (F-CapMix) offers an innovative approach to harnessing this energy potential. However, conventional F-CapMix systems encounter limitations in power density due to the restricted charge storage capacity inherent in porous carbon materials, which operate via the electrical double-layer mechanism. In this study, we introduce manganese dioxide-coated activated carbon (MO@AC) as a novel flow-electrode material for F-CapMix applications, placing specific emphasis on the introduction of an asymmetric flow-electrode system. We conduct a comprehensive assessment of the electrochemical properties of both activated carbon (AC) and MO@AC-based flow-electrodes, with particular attention to their suitability as positive and negative electrodes for symmetric and asymmetric F-CapMix configurations. Notably, it becomes evident that remarkable performance enhancements are exclusively observed in the context of the asymmetric F-CapMix system, thus underscoring the heightened efficacy of the MO@AC material within this asymmetric framework. Remarkably, employing MO@AC as the flow-electrode in the asymmetric F-CapMix configuration yields an impressive power density of 2.22 W/m² through reversible redox reactions involving Na⁺ ions. These findings not only expand the horizons of potential applications but also underscore the transferability of our strategies to various materials engaged in redox reactions with Na⁺ and Cl^– ions within the realm of F-CapMix systems.