Electrochemical Enhancement of Vanadium and Manganese Redox Couples Using N-Doped Carbon Nanomaterials Deposited on Carbon Cloth Electrodes

Abstract Improving interfacial charge-transfer kinetics at porous carbon electrodes remains a central challenge in redox flow battery (RFB) electrochemistry, particularly for kinetically demanding redox couples such as Mn2+/Mn3+. Herein, we report a binder-free horizontal electrophoretic deposition (EPD) strategy to assemble nitrogen-doped carbon nanotubes (N_CNTs) and nitrogen-doped reduced graphene oxide (N_rGO) directly onto woven carbon cloth substrates, enabling controlled nano structuring of electrochemically active interfaces without polymeric binders. Structural and spectroscopic characterizations (SEM, TEM, EDS, XRD, FTIR, Raman and XPS) confirm successful coating of carbon nanomaterials on the cloth and incorporation of nitrogen, introducing defect-rich graphitic domains and enhanced surface functionality. Electrochemical evaluation using cyclic voltammetry and impedance spectroscopy reveals significantly enhanced charge-transfer kinetics, reduced interfacial resistance, and increased diffusion coefficients for V2+/V3+, VO2+/VO2+, and Mn2+/Mn3+ redox couples for N-doped modified electrodes. Particular emphasis is placed on understanding how nanoscale electrode architecture and nitrogen-induced defect chemistry influence the intrinsically sluggish Mn2+/Mn3+ redox reaction, which remains a bottleneck in V/Mn redox flow batteries. When implemented in full redox flow battery cells, N_CNT-modified electrodes deliver reduced polarization losses and peak power densities of 310 and 360 mW cm−2 in all-vanadium and vanadium−manganese systems, respectively. Improved energy efficiency above 70% was achieved in both systems. Stable performance over 200 charge−discharge cycles at 100 mA cm−2 highlights the critical role of nitrogen-induced defect sites in promoting electrochemical reversibility, enhancing interfacial wettability, and modifying the local electron density, thereby effectively overcoming the intrinsic kinetic limitations of the manganese redox chemistry. These results demonstrate that binder-free electrophoretic nano structuring offers a scalable and electrochemically robust route to tailoring carbon electrode interfaces for next-generation flow battery electrodes by providing abundant, electrochemically accessible active sites.