High-Performance Flow-Field Structured Iron-Chromium Redox Flow Batteries for Large-Scale Energy Storage

Abstract

The conventional flow-through structured ICRFBs have to employ thick carbon felts (typically 3.0-6.0 mm) as the electrodes to circumvent high pump loss, which inevitably results in high ohmic resistance, low operating current densities (around 80 mA cm-2) as well as cumbersome and costly cell stacks. Increasing the operating current density/power density is an effective strategy to reduce the cell stack size and cost. Recently, a flow-field structured ICRFB with thin carbon paper electrodes demonstrates a significantly increased operating current density of 200 mA cm-2 at the energy efficiency of 79.6% mainly due to the reduced ohmic resistance [1]. Further enhancement of ICRFB performance is achieved by adopting the interdigitated flow fields, which enhances the active species transport at the porous electrode and enables a more uniform catalyst distribution [2]. In addition, the effects of design parameters including electrode compression ratio, electrode pretreatment intensity, membrane thickness and catalyst loading on the ICRFB charge-discharge performance have been are investigated [3]. Results show that: i) with a thin NR-211 membrane and a high electrode compression ratio of 62.5%, the operating current density of the ICRFB can reach as high as 480 mA cm-2 at an energy efficiency of higher than 80%; ii) the bismuth catalyst loading has insignificant effect on the battery performance in the range of 0.52-10.45 mg cm-2; iii) the moderately oxidative thermal pretreatment of the electrode improves the energy efficiency compared to the as-received electrode while the electrode prepared with a harsh pretreatment deteriorates the battery performance; and iv) for the present ICRFBs operating at both 25oC and 65oC, the dominant loss is identified to be ohmic loss rather than kinetics loss.