High-Entropy Oxide of (BiZrMoWCeLa)O₂ as a Novel Catalyst for Vanadium Redox Flow Batteries

Abstract

In this study, new fluorite high-entropy oxide (HEO), (BiZrMoWCeLa)O 2 , nanoparticles were produced using a surfactantassisted hydrothermal technique followed by calcination and were used as novel catalytic materials for vanadium redox flow batteries (VRFBs). The HEO calcined at 750 °C (HEO-750) demonstrates superior electrocatalytic activity toward V 3+ /V 2+ and VO 2+ /VO 2 + redox couples compared to those of cells assembled with other samples. The charge−discharge tests further confirm that VRFBs using the HEO-750 catalyst demonstrate excellent Coulombic efficiency, voltage efficiency, and energy efficiency of 97.22, 87.47, and 85.04% at a current density of 80 mA cm −2 and 98.10, 74.76, and 73.34% at a higher current density of 160 mA cm −2 , respectively. Moreover, with 500 charge−discharge cycles, there is no discernible degradation. These results are attributed to the calcination heat treatment, which induces the formation of a new single-phase fluorite structure, which facilitates the redox reactions of the vanadium redox couples. Furthermore, a high surface area, wettability, and plenty of oxygen vacancies can give more surface electroactive sites, improving the electrochemical performance, the charge transfer of the redox processes, and the stability of the VRFBs' electrode. This is the first report on the development of fluorite structure HEO nanoparticles in VRFBs, and it opens the door to further research into other HEOs.

Heteroatom-Rich Hierarchical Porous Biomass Carbon for Vanadium Redox Flow Batteries

“…At the same current, the voltage of the cell with ABC-N-CF is higher than that of the blank cell, indicating that the polarization inside the cell with ABC-N-CF is smaller, resulting in lower voltage loss. The kinetic reversibility of the electrode influences the EE, whereas the voltage drop and polarization on the electrode surface affect VE . Therefore, improving the electrochemical performance can boost these two key parameters.…”