Differential charge density of graphite felt and nickel oxide and differential charge density of Fe and Cr adsorbed on graphite felt and nickel oxide. The dangling bonds of surface oxygen atoms in NiO can form bonding orbitals with Fe/Cr ions, achieving a maximum adsorption energy of 2.04 eV·Å⁻

Herein, the performance of nickel-oxide-modified graphite felts as electrode materials for Fe/Cr liquid flow batteries is investigated by combining density functional theory and experiments. The results show that the adsorption of NiO on Fe/Cr ions is more stable than that on graphite felt, and more electrochemically active sites are provided. The charge transfer after adsorption is larger, which is more conducive to the redox reaction during the charging and discharging processes. Finally, the experimental results further prove that the first discharge capacity of the nickel oxide-modified graphite felt reaches 22.0 Ah L−1$^{-1}$, which is much higher than that of the unmodified graphite felt (12.4 Ah L−1$^{-1}$). In addition, its energy efficiency could reach up to 59.5%, which is 27.3% higher than that of the original electrode.