Dynamic hydrogen bubble template electrodeposited Bi on graphite felt and the effect of its post-processing in vanadium redox flow batteries

Abstract

In this work, the very effective synthesis method of dynamic hydrogen bubble template (DHBT) electrodeposition has been employed for the first time in decorating graphite felt (GF) with high surface area bismuth nanoparticles as the negative electrode in vanadium redox flow batteries (VRFBs). The electrodes synthesized by the DHBT method were compared with other reported systems, such as Bi₂O₃ particles impregnated on GFs and adding Bi³⁺ directly into the vanadium electrolyte. In this comparison, the DHBT-synthesized samples showed significantly improved kinetics of the V³⁺/V²⁺ redox reactions. Besides, it can be demonstrated that the performance is significantly affected by the post-processing and drying conditions of the synthesized electrode owing to alterations in morphologies, distributions of Bi, impurities, etc. Precise kinetic analysis was performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) normalization in a 3-electrode setup. Surface morphology, catalyst composition and stability were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and inductively coupled plasma-optical emission spectroscopy (ICP-OES), respectively. Full-cell polarization tests demonstrated that the air dried DHBT Bi modified graphite felt electrode as negative electrode could achieve a power density of 416.6 mW cm⁻² at a current density of 480 mA cm⁻². Additionally, the observed electrolyte utilization is reported as high as 37.5 Ah L⁻¹, while the energy efficiency stabilized at around 78% after 100 cycles at a current density of 25 mA cm⁻².