Carbon model surfaces for the improved kinetics of vanadium redox couples Maída Aysla Costa de Oliveira 1 , Hugo Nolan 1 , Christian Schröder 1 , Marc Brunet-Cabré 1 , Kim McKelvey 1,2 and Paula E. Colavita 1 1 School of Chemistry, Trinity College Dublin and 2 School of Chemical and Physical Science, Victoria University of Wellington To expand the integration of renewable energy sources in the electricity grid, low-cost materials, and high efficiency storage technologies and devices are still required. Among the different electrochemical systems, vanadium redox flow battery (VRFBs) technology holds high promise for coupling storage to renewables due to advantages such as flexible modular design, relatively low cost, high storage capacity, long service life, and deep discharge capability. A VRFB consists of two tanks with vanadium redox couples, separated by an ion-exchange membrane and circulated through a cell composed of porous electrodes at which the charge/discharge reactions take place [1] . Nevertheless, reducing kinetic barriers for vanadium redox couples and understanding the reaction mechanism at the electrode/electrolyte interface for the oxidation and reduction processes remain critical for designing high-performing VRFB devices [2] . Conventional graphitic carbon electrodes are often employed to achieve the required high efficiency, due to having a low cost, high surface area, high conductivity, and wide charge/discharge voltage. However, the kinetics of both V +3 /V 2+ and VO +2 /VO 2 + redox couples is generally sluggish at conventional carbon electrodes and their activity can limit the overall performance due to high overpotentials and undesirable efficiency losses [3] . Heteroatom functionalization, in particular with nitrogen sites, might enhance the electron transfer kinetics during the redox reactions and improve wettability and electrochemically active area at carbon electrodes [4] . In this study, we developed carbon model surface electrodes with controlled Nitrogen- sites density and controlled distribution, for the fundamental understanding of the chemical, structural and electronic effects on charge transfer kinetics of vanadium redox couples. A combination of surface chemistry, morphological and conventional electrochemical methods were used to evaluate the N-doped carbon thin film architectures and the kinetic performance of VO +2 /VO 2 + redox couple at the electrode/electrolyte interface. The set of results demonstrated that both N-site type and carbon organization affect charge transfer impedances and rate- determining steps involved in the charge/discharge process. The controlled combination and density of pyridinic-N with pyrrolic-N sites in/on the carbon thin film electrodes affected positively the kinetic of VO +2 /VO 2 + . Thus, from the proposed materials we will discuss the implications of our findings for the design of carbon model surface for VRFB performance. References 1. Meskinfam, et al., Interaction of vanadium species with a functionalized graphite electrode: A combined theoretical and experimental study for flow battery applications (2018), 420,142. 2. Choi, et al., Understanding the redox reaction mechanism of vanadium electrolytes in all-vanadium redox flow batteries, J Energy Storage (2019), 21, 327. 3. Behan, et al., Combined optoelectronic and electrochemical study of nitrogenated carbon electrodes. J Phys Chem C (2017), 121, 6596. 4. Tripathi et al., Interfacial co-polymerization derived nitrogen doped carbon enables high-performance carbon felt for vanadium flow batteries. J. Electrochem (2021), 168, 110548.
P153E
Made with FlippingBook Learn more on our blog