In-situ electrodeposition of homogeneous and dense bismuth nanoparticles onto scale-up graphite felt anodes for vanadium redox flow batteries

The uniform and dense distribution of highly active electrocatalysts onto graphite fibers of scale-up anodes is essential for the engineered vanadium redox flow batteries to be operated efficiently and stably. In this work, a new in-situ electrodeposition strategy of bismuth is devised by using a catholyte with a low concentration of vanadium ions (33 mM V3+). Compared with the conventional method using a catholyte with a high concentration of vanadium ions (1700 mM VO2+), the present strategy renders Bi nanoparticles not being oxidized by VO2+ transported across the membrane from the catholyte, enabling bismuth nanoparticles with sizes of about 58 nm being uniformly and densely electrodeposited onto graphite fibers of an anode (117 cm−2) at an extremely low electrodeposition current density (2 mA cm−2). The vanadium redox flow battery with the present scale-up anode achieves an energy efficiency of 76.3% even at a current density of 300 mA cm−2, which is higher than that of batteries with a conventional method treated anode (74.9%), and an untreated (73.3%). Furthermore, the battery with the present scale-up anode shows an energy efficiency of 82.5% and stable operation for 200 cycles at a current density of 200 mA cm−2. •Bismuth is electrodeposited with a catholyte containing low VO2+ concentration.•The diameters of bismuth is reduced to 40 nm.•The distribution of bismuth is controlled to dense and uniform.