Ultrathin Conformal oCVD PEDOT Coatings on Carbon Electrodes Enable Improved Performance of Redox Flow Batteries

Surface engineering of porous carbon electrodes is an effective strategy to enhance the power output of redox flow batteries (RFBs) and may enable new cost reduction pathways for energy storage. Here, a surface modification strategy that enhances the electrochemical performance of RFBs in iron-based electrolytes is demonstrated. Nanometric films of poly(3,4-ethylenedioxythiophene) (PEDOT) are grown conformally onto carbon cloth electrodes using oxidative chemical vapor deposition (oCVD) and the impact of film properties on electrode performance in model iron-based electrolytes is investigated. Depositing oCVD PEDOT films on the electrode surface is found to reduce ohmic, kinetic, and mass transport resistances, with the highest current densities and lowest resistances observed for electrodes coated with a ≈78 nm thick film. As compared to unmodified electrodes, coated electrodes enhance the maximum obtained current density at an applied overpotential of 350 mV by 6.7× and 3.7× in iron sulfate and iron chloride, respectively. The oCVD PEDOT film described here represents an initial step toward electrode surfaces of tailored activity, selectivity, and wettability for specific RFB chemistries and, more generally, electrochemical systems with liquid-phase reactants.