MoO3 modified graphite felt electrode for Zn-Fe redox flow cell applications

Modular scalability, inherent safety, decoupling of energy and power, and extended lifetime are considered major advantages of Zn-Fe redox flow batteries . However, the zinc dendrite formation, hydrolysis of the Fe 3+ , hydrogen evolution , unfair reaction kinetics, etc. are restricting this Zn-Fe RFB's further developments. In recent times, the metal oxide-based electrocatalysts promote the reaction kinetics of the redox reaction , which improves the flow cell performance. In this work, MoO 3 -attached graphite felt is used as a positive electrode , which enhances the redox kinetics of the Fe 2+ /Fe 3+ redox reactions. The attachment of the MoO 3 on the graphite felt is confirmed using X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray (EDX) characterizations. The reaction kinetics of Fe 2+ /Fe 3+ redox reaction is analyzed in 0.01 M FeCl 2 electrolyte for both bare GF and MoO 3 @GF electrodes using cyclic voltammetry . The MoO 3 @Graphite electrode shows a highly improved diffusion coefficient of the order of 1.4 × 10 −6 (anodic) and 1.5 × 10 −6 cm 2 s −1 (cathodic) than that of the bare graphite electrode (anodic: 7.8 × 10 −7 ; cathodic: 12.9 × 10 −7 cm 2 s −1 ). Further, the polarization studies of the flow cell having MoO 3 @GF ensured the highly improved power density of 65 mW cm −2 , which is much better than the bare GF-based flow cell. Using an ion exchange membrane , the flow cell shows an enhanced Coulombic and energy efficiency of 93 % and 75 %, respectively at the 60 th cycle at 20 mA cm −2 than the porous separator-based flow cell. Thus, it is believed that the MoO 3 @GF electrode, along with the Nafion-117 membrane, is a potential candidate for Zn-Fe RFB applications. Schematic Representation of the Modified Zn-Fe Redox Flow Cell • MoO 3 @GF electro-catalyst has been used for improving Fe 2+ /Fe 3+ . • The flow cell having MoO 3 @GF shows a high Coulombic efficiency of 93 %. • The flow cell having MoO 3 @GF shows a high energy efficiency of 75 %. • Surface-controlled kinetics of Fe 2+ /Fe 3+ redox reaction have been improved.