High-Performance Asymmetric Flow-Electrode Capacitive Mixing with MnO₂-Coated Activated Carbon Flow-Electrode for Energy Harvesting from Salinity Gradient Power

Flow-electrode capacitive mixing (F-CapMix) is a promising energy harvesting system, utilizing the salinity gradient difference between seawater and river water. However, the conventional F-CapMix system has a low power density due to the limited charge storage of porous carbon materials through the electrical double layer. In this study, we first report manganese dioxide-coated activated carbon (MO@AC) as a flow-electrode material for the F-CapMix system. MnO₂nanoparticles could be easily decorated on the surface of activated carbon (AC) by the reduction of KMnO₄in an acidic medium. We systematically study electrochemical properties of AC and MO@AC-based flow-electrodes as positive and negative electrodes for both symmetric and asymmetric F-CapMix systems. The asymmetric F-CapMix system employing the MO@AC flow-electrode exhibits an outstanding power density of 2.22 W/m²through the reversible redox reaction with Na⁺ions. Our strategies can be extended to other materials that have redox reactions with Na⁺and Cl^-ions for the F-CapMix system.