Deposition of Li/Al layered double hydroxides on the graphite felts for the performance improvement of an all-vanadium redox flow battery

Abstract

Porous graphite felts (GFs) play an important role in all-vanadium redox flow batteries (VRFBs) because a redox reaction occurs on the surface of the graphite’s fibers. In order to enhance the electrochemical performance of the GFs, a novel method is developed to modify the surface of GFs by decorating layered double hydroxides (LDHs) with Ni or NiO nanoparticles. For a comparative study, GFs treated with acid and heat are also prepared as porous electrodes of the VRFB. The performance of VRFBs with GFs treated with various methods and investigated the characteristics of these GFs. The results show that GFs decorated with LDH (including Ni and NiO nanoparticles) can improve the energy efficiency of the VRFB by 5% compared with acid- or heat-treated GFs. X-ray photoelectron spectroscopy measurements indicate that the improvement in the heat-treated graphite fibers’ wettability is due to a reduction in the O/C ratio and an increase in the C–O/C = O ratio on the graphite fibers. An H2 reduction treatment formed the metallic Ni on the LiAlO platelets. The calcination heat treatment in the air created NiO to improve the active surface area and therefore enhance the redox reaction.