MoO₃-Deposited Graphite Felt for High-Performance Vanadium Redox Flow Batteries

Abstract

To overcome the challenge of the low power density of all-vanadium flow batteries, electrodes with enhanced electrochemical activity are necessary. A facile and scalable impregnation process was employed to deposit MoO 3 particles on the surface of a graphite felt (GF) (MoGF) electrode. In the cyclic voltammetry profiles, the as-prepared electrode exhibits superior electrocatalytic activity toward the redox couple of VO 2+/ VO 2 + , significantly enhancing the reversibility, as indicated by the substantially reduced peak separation from 490 mV (pristine GF) to 245 mV (MoGF). The full-cell performance was also studied, where MoGF exhibited an extraordinary voltage efficiency (VE) of 71.42% at a high current density of 250 mA cm −2 . The highest current density of most works is limited to ≤200 mA cm −2 with very few reporting the cell performance at 250 mA cm −2 , which has generally achieved a VE of 66%. With regard to electrolyte utilization, the cell employing MoGF demonstrated a 139.69% improvement over the cell employing pristine GF at 150 mA cm −2 . Furthermore, the cell employing GF underwent 50 charge−discharge cycles at 100 mA cm −2 , delivering a stable VE of 87.1%. Physicochemical and electrochemical characterizations were carried out to unveil the catalytic effect of the deposited layer, which confirmed that not only orthorhombic MoO 3 with high electrochemical activity and electrical conductivity was deposited but also a larger surface area and adequate oxygen functional groups were obtained through this facile fabrication process.

Carbon Nanofibers Coated with MOF-Derived Carbon Nanostructures for Vanadium Redox Flow Batteries with Enhanced Electrochemical Activity and Power Density

“…Graphite felt and carbon paper, which are commonly used as electrodes in VRFBs, show poor electrochemical activity, leading to limited power and current outputs. To address this issue, structural engineering and surface modifications are suggested to design new carbon electrodes. − Although absorption of active species such as metals, metal oxides, and metal nitrides on the felt support is used in the electrode development, their high-cost, instability, and poor electronic conductivity inhibit application in the battery system. − Structural engineering involves designing nanoporous structures to decorate complex interfaces. − A sacrificial template is used to introduce nanopores on graphite felt, resulting in an improved energy efficiency . Similarly, a wood-derived carbon electrode is used, which improves the battery performance due to the presence of aligned channels and large pores .…”

The Renaissance of the Zn-Ce Flow Battery: Dual-Membrane Configuration Enables Unprecedentedly High Efficiency

“…EIS was performed on the GF-cell and GF-cell_FT at 50% SOC (Figure S9), in which the GF-cell_FT demonstrated alleviated cell polarization due to the smaller electrolyte resistance of the iThub. Although the theoretical capacity of Zn-Ce RFBs is similar to that of VRFB, , the discharge capacity of conventional Zn-Ce RFBs is far lower than that of VRFB due to the low CE, which can be addressed by our dual-membrane design. While the discharge capacity of the GF-cell_FT and GF-cell is elevated to the same level as for VRFB (12–14 Ah/L), ,, the discharge energy density is significantly higher than that of VRFB, owing to the high discharge voltage.…”

“…Although the theoretical capacity of Zn-Ce RFBs is similar to that of VRFB, , the discharge capacity of conventional Zn-Ce RFBs is far lower than that of VRFB due to the low CE, which can be addressed by our dual-membrane design. While the discharge capacity of the GF-cell_FT and GF-cell is elevated to the same level as for VRFB (12–14 Ah/L), ,, the discharge energy density is significantly higher than that of VRFB, owing to the high discharge voltage. In addition, the polarization curve of the GF-cell recorded at 70% SOC is shown in Figure c, in which a peak power density of 360.4 mW cm –2 is demonstrated.…”