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

Abstract

broad adoption, motivating research into optimizing reactor design, electrolyte formulations, and separation strategies. The porous carbon electrode is a critical component of the RFB stack, providing active sites for redox reactions, controlling electrolyte distribution and pressure drop, and cushioning compressive forces required to seal the system and minimize contact resistances. [6] While functional, the electrodes used in advanced RFBs, which are typically based on porous carbon and graphite papers, cloths, or felts, generally possess low surface area (≈0.1-10 m 2 g −1), spatially varying surface chemistry, and poor aqueous wettability. [7] To address these limitations, electrodes are commonly oxidatively pretreated, via thermal, [8-11] electrochemical, [12] or chemical means, [13,14] which can simultaneously increase surface area and introduce oxygen-rich functional groups on the electrode surface that improve wetting and reaction kinetics. While effective, these methods offer limited control of specific surface chemistry and compositional uniformity across the 3D geometry. A potentially effective strategy for tailoring electrode-electrolyte interfaces is through the deposition of conductive polymeric overlayers, which have been shown to enhance the areal energy and power density in supercapacitors by improving pseudocapacitance, [15] and stabilize the structure and thermal stability of the electrode-electrolyte interface in lithium-ion batteries with nickel-rich positive electrodes. [16] These studies utilized continuous polymer layers, as thin as 3 nm, grown by oxidative chemical vapor deposition (oCVD) to support facile electrical and ionic conduction. In contrast to solution-applied layers, the oCVD films conformally encapsulated the nanostructured surfaces, leaving void space to enable changes in polymer layer thickness upon ion exchange without the development of significant mechanical strain. Additionally, conformal coverage maintains high surface area for effective contact with the electrolyte. Here, we explore the potential of oCVD processing to improve the performance of carbon fiber-based electrodes in 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 maxim...

Optimizing the Optoelectronic Properties of Face‐On Oriented Poly(3,4‐Ethylenedioxythiophene) via Water‐Assisted Oxidative Chemical Vapor Deposition

“…Experimental variation of the OSR was facilitated by the similar vapor pressures of SbCl 5 oxidant and EDOT monomer. Control of OSR is more difficult for the highly volatile liquid oxidant, VOCl 3 (P sat = 17.8 Torr at 25 °C), [7,40] or the low volatility solid oxidant, FeCl 3 (P sat = 1 Torr at 194 °C, and negligible at 25 °C). [5,29,41,42] The SbCl 5 oxidant is a liquid of moderate volatility at ambient temperature (P sat = 1.2 Torr at 25 °C) [42] and can be readily introduced into the oCVD reactor ( Figure 1a).…”

“…The cross-sectional SEM image of PEDOT thin film grown on a wider area of the trench silicon wafer is exhibited in Figure S7, Supporting Information. While the oCVD method provides highly conformal and uniform PEDOT thin films, the spun-cast PEDOT:PSS does not exhibit such advantages [2,40,60] due to the surface tension effects and formation of an air-gap, bridging, and meniscus. [1,40] Depositing ultrathin conformal oCVD PEDOT coating on high aspect ratio features yields significant advantages in many advanced technologies, including wearable electronics, [61] and electrochemical energy storage devices.…”

“…[1,40] Depositing ultrathin conformal oCVD PEDOT coating on high aspect ratio features yields significant advantages in many advanced technologies, including wearable electronics, [61] and electrochemical energy storage devices. [40,62]…”

Overcoming intra-molecular repulsions in PEDTT by sulphate counter-ion

“…The rising importance of conductive polymers is beyond discussion: (light-weight) solar applications (1)(2)(3)(4), biointegration (5), pressure sensors (6), and actuators (7), as well as thermoelectric applications (8) and batteries (9) were demonstrated. Beyond diversity in application, high conductivities (> 6000 S cm -1 ) (10-13) challenging those of inorganic materials (14), and even semi-metallic (15,16) and metallic properties (17)(18)(19)(20)(21) were shown to be possible.…”

Controlled Release Utilizing Initiated Chemical Vapor Deposited (iCVD) of Polymeric Nanolayers

“…For example, a film which bridges the open space between different fibers results in blockage of the pore structure within a fabric. Formation of the undesirable bridging films can be driven by surface-tension based phenomena present in liquid-phase coating processes (Heydari Gharahcheshmeh et al, 2020 ).…”