Jo Jan 26, 2024

Redox flow battery (RFB) is an electrochemical device that stores and releases energy through redox reactions of active ion species in electrolyte. The main advantage of RFB over other electrochemical devices such as lead acid battery and lithium ion battery is that the power system could be made very flexible because of the independence of its power from its energy and that its cost per energy in high-capacity systems is particularly low.

Up to now, there have been developed many kinds of RFBs and they have anolyte and catholyte containing different active ion species. An ion selective membrane is introduced to prevent the active ion species from mixing. During charge and discharge, the anolyte and the catholyte are cycled through their own reservoirs by using pumps, respectively. Examples of RFBs include all-vanadium series, iron-chromium series and bromine-polysulfide series. The ion selective membrane for these RFBs is very expensive and should satisfy very strict requirements for several aspects including ion selectivity, electric conductivity and chemical stability. For this reason, recent works are targeted to using no membranes.

SLFB is acknowledged as a promising battery and it attracts attentions of researchers because it needs no membrane and is cheap. Unlike RFBs, SLFB does not require any ion selective membranes because both the anolyte and the catholyte are the same. Hence, SLFB possesses only one electrolyte reservoir and one flow canal, thus making its design simple. Moreover, electrolyte cross through the medium of diaphragm never exists and the possibility of electrolyte leaking diminishes because of a small number of cell components.

Kim Ju Song, a researcher at the Faculty of Chemical Engineering, has suggested HBF4 and Pb(BF4)2 as the electrolyte of SLFB because it is commercially favorable with a low cost and has a high solubility of lead and conductivity compared to the methylsulfonic acid (MSA), and he has investigated the availability of fluoroboric acid and lead fluoroborate prepared with recovered lead as the electrolyte of SLFB.

He first measured the average cell efficiency, average quantum efficiency and average voltage efficiency of the SLFB using lead fluoroborate prepared with recovered lead. Then, he compared them with those of conventional MSA electrolyte. As many as 30 times of charge/discharge tests showed that the average cell efficiency, average quantum efficiency and average voltage efficiency of the recovered lead electrolyte are much better than the efficiencies obtained in methylsulfonic acid electrolyte, and that the average charge/discharge efficiency was 87 % and there was no significant decrease in the performance during charge/discharge cycles, thus proving the availability of electrolyte prepared with recovered lead for SLFB.

You can find the details in his paper “Electrochemical properties of electrolyte for lead fluoroborate redox flow battery prepared with recovered lead” in “Journal of Saudi Chemical Society” (SCI).