Nanoneedle array structure optimization-induced mass transfer in all-vanadium flow batteries

Abstract

This paper employs a robust acid pretreatment to activate the graphite felt electrode, subsequently facilitating the generation of nickel cobalt oxide (NiCoO₂) nano-needle arrays on the surface of the graphite felt electrode through a hydrothermal method. Additionally, the paper demonstrates the successful doping of the NiCoO₂ structure with nitrogen through the utilization of an ammonia annealing process. The experimental results reveal that this modification initiative enlarges the BET specific surface area of the electrode by a factor of sixteen. Furthermore, the needle array structure not only increases the delivery of active substances but also greatly facilitates the electrochemical reaction. The electrochemical performance of the modified graphite felts was markedly enhanced in comparison to that of the pristine graphite felts, due to the combined effect of the Ni-Co oxides' efficient electrocatalytic ability and the improvement of the mass transfer ability of the electrode resulting from the alteration of the electrode surface structure. The doping of the metal oxides with nitrogen can further increase their conductivity, thereby enhancing their catalytic performance for redox reactions. The Multiphysics simulation results on the electrode surface demonstrate that the upright channels between the needle arrays facilitate the full and rapid reaction of vanadium ions on the electrode surface, enabling the products to be detached from the electrode in a timely manner, which in turn reduces the concentration polarization on the electrode surface.