Harvesting blue energy via flow-electrode capacitive mixing (F-CapMix): From fundamental understanding to scalable power generation

Abstract

Flow-electrode capacitive mixing (F-CapMix) is an emerging electrochemical technology for harvesting salinity gradient energy using carbon-based slurry electrodes and ion-exchange membranes. Unlike traditional static CapMix systems, F-CapMix enables continuous cycling between high- and low-salinity streams, overcoming saturation limits of fixed electrodes. The energy extraction is driven by either capacitive double-layer expansion or Donnan potential mechanisms, depending on membrane configuration and operating mode. Recent progress has been made in optimizing flow electrode formulations, including hybrid mixtures of activated carbon and graphitic additives, as well as integration of pseudocapacitive materials to enhance energy density. System-level innovations, such as interfacial engineering, vortex-enhanced channel designs, and scalable modular stacks, address key challenges in flow distribution, ion accessibility, and long-term stability. Numerical simulations and experimental validations highlight critical trade-offs between energy output and pumping losses, guiding the rational design of flow fields and cell geometries. This review aims to understand the governing mechanisms, materials, and operating modes of F-CapMix. It critically assesses recent progress in interfaces, architectures, and flow management, and outlines research priorities for stability, manufacturability, and field validation.