High-Performance Carbon Slurries with an Improved Electronic Conductive Network for Electrochemical Flow Capacitors

Abstract

The existence of an excess liquid phase results in weak contact between activated carbon particles, leading to high-concentration polarization, which is a critical factor in the incomplete percolation network of the electrode slurry that severely restricts electron transfer in the solid phase and ion migration in the liquid phase. In this study, we developed an innovative aqueous electrode slurry with an electronic conductive network, which was composed of activated carbon (AC) particles (Kuraray YP-80F), KOH, potassium ferricyanide and Ketjen black (KB) as electronic conductive additives, to enhance the charge transfer through the conductive network and ion adsorption on the surface in AC particles. The results of the three-electrode tests showed that the carbon slurry with a multi-dimensional conductive network exhibited a high specific capacity of 408 F/g at a scan rate of 2 mV/s, and even maintained a specific capacity of 111 F/g at 100 mV/s. It was further confirmed through electrochemical analysis and computational fluid dynamics (CFD) simulation that the addition of conductive agents enables the formation of a slurry with point-to-line-to-surface connectivity, thereby forming a robust charge percolation network along various paths, which is conducive to charge transfer. Finally, we assembled a symmetric electrochemical flow capacitor and conducted electrochemical performance tests under flow conditions. The constant current charge-discharge curves exhibited nearly symmetrical triangular shapes, indicating a diffusion-dominated double-layer mechanism. The specific capacity of the slurry with an electronic conductive network reached 473 F/g under flow conditions. This work provides a new strategy for the design of high-energy-density electrochemical flow capacitors (EFCs) by constructing an electronic conductive network composed of KB.

Keywords: Electrochemical flow capacitor, Carbon slurry, Electronic conductive network