PEDOT:PSS‐CNT Composite Particles Overcome Contact Resistances in Slurry Electrodes for Flow‐Electrode Capacitive Deionization

Abstract Activated carbon (AC) particles constitute the current material of choice concerning the preparation of flow electrodes for flow‐electrode capacitive deionization (FCDI). They are inexpensive, mass‐producible, highly conductive, and exhibit a large specific surface area for ion adsorption. However, despite recent advances concerning the modification of AC slurries, their density, and hydrophobicity still constitute major challenges regarding particle aggregation, sedimentation, and pumpability, restricting their particle load to approximately 25 wt.%. Since the particle volume fraction directly correlates to the chance of particle contact, which dictates the charge transfer and hence the degree of flow electrode utilization, the development of AC‐based slurries seems to stagnate. This study addresses these challenges by investigating poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)‐based suspensions as an alternative to conventional carbon‐based flow electrodes. The corresponding conductive hydrogel particles feature softness, internal porosity, low density, hydrophilicity, and a mass‐specific salt adsorption capacity that exceeds AC by up to ten times. FCDI experiments can reveal that, contrary to AC, the inherent properties of PEDOT:PSS‐based particles simplify the slurry preparation process and enable flow electrode circulation at significantly higher particle volume fractions. These results suggest that PEDOT:PSS‐based hydrogel particles are a promising candidate to overcome the percolation and contact‐related challenges of state‐of‐the‐art AC slurries.