Prussian blue analogue-assisted asymmetric flow-electrode capacitive mixing (F-CapMix) with high positive net power density

Abstract

Flow-electrode capacitive mixing (F-CapMix) is a promising technology for harvesting renewable energy from the salinity gradient between seawater and river water. However, conventional F-CapMix systems relying exclusively on activated carbon (AC) flow-electrodes face intrinsic limitations regarding power generation performance. In a symmetric configuration, the potentials of both flow-electrodes are established within a similar range, resulting in a low initial open-circuit voltage (OCV) that leaves the membrane Donnan potential arising from the salinity gradient as the sole driving force for power generation. In this study, we established a high-performance asymmetric flow-electrode system by incorporating NiFe-PBA into an AC-based cathode. Mechanistically, the NiFe-PBA induces a potential tuning effect that positively shifts the equilibrium potential of cathode, thereby significantly elevating the overall cell OCV. Furthermore, the highly reversible redox reactions of NiFe-PBA substantially increase the ion storage capacitance and facilitate charge transfer, effectively reducing the internal cell resistance. Driven by the synergy of this potential tuning effect and enhanced electrochemical kinetics, the asymmetric system achieved a maximum gross power density of 3.03 W/m2, which is a more than threefold increase compared to the symmetric counterpart. Furthermore, through systematic optimization of the flow-electrode and feed water flow rates, a superior net power density of 1.96 W/m2 was achieved even after accounting for the pumping energy required for system operation. Copyright