Synthesis and Characterization of Dense Carbon Films as Model Surfaces to Estimate Electron Transfer Kinetics on Redox Flow Battery Electrodes.

Redox flow batteries (RFBs) are a promising electrochemical technology for the efficient and reliable delivery of electricity, providing opportunities to integrate intermittent renewable resources and to support unreliable and/or aging grid infrastructure. Within the RFB, porous carbonaceous electrodes facilitate the electrochemical reactions, distribute the flowing electrolyte, and conduct electrons. Understanding electrode reaction kinetics is crucial for improving RFB performance and lowering costs. However, assessing reaction kinetics on porous electrodes is challenging as their complex structure frustrates canonical electroanalytical techniques used to quantify performance descriptors. Here, we outline a strategy to estimate electron transfer kinetics on planar electrode materials of similar surface chemistry to those used in RFBs. First, we describe a bottom-up synthetic process to produce flat, dense carbon films to enable the evaluation of electron transfer kinetics using traditional electrochemical approaches. Next, we characterize the physicochemical properties of the films using a suite of spectroscopic methods, confirming that their surface characteristics align with those of widely used porous electrodes. Last, we study the electrochemical performance of the films in a custom-designed cell architecture, extracting intrinsic heterogeneous kinetic rate constants for two iron-based redox couples in aqueous electrolytes using standard electrochemical methods (i.e., cyclic voltammetry, electrochemical impedance, and spectroscopy). We anticipate that the synthetic methods and experimental protocols described here are applicable to a range of electrocatalysts and redox couples.

Branched aramid nanofiber-polyaniline electrodes for structural energy storage.

Strong electrodes with good energy storage capabilities are necessary to accommodate the current needs for structural and flexible electronics. To this end, conjugated polymers such as polyaniline (PANI) have attracted much attention due to their exceptional energy storage performance. However, PANI is typically brittle and requires the use of substrates for structural support. Here, we report a strategy for developing free-standing structural supercapacitor and battery electrodes based on PANI. More specifically, aniline is polymerized in the presence of branched aramid nanofibers (BANFs) and single walled carbon nanotubes (SWCNTs). This results in a network morphology that allows for efficient load transfer and electron transport, leading to electrodes with capacity values up to 128 ± 5 mA h g-1 (vs. a theoretical capacity of 147 mA h g-1), Young's modulus of 4 ± 0.5 GPa, and tensile strength of 40 ± 4 MPa. Furthermore, the charge storage mechanism is investigated, in which both Faradaic and non-Faradaic contributions are observed. This work demonstrates an efficient strategy for designing structural electrodes based on conjugated polymers.