A Hydrogen–Bromate Flow Battery for Air‐Deficient Environments

Abstract

A concept of high energy density (ED) hydrogen–bromate flow battery was supported by experiments with flow cells with 0.1 to 50 cm2 apparent areas. H2/NaBrO3 flow cells with H2 gas diffusion anode, proton exchange membrane (PEM), and carbonaceous flow‐by or flow‐through cathodes were employed. Estimates show that the theoretical ED of the H2/bromate flow battery (HBFB) exceeds the ED of H2/O2 fuel cells (FC) in air‐deficient environments. At the cathode of the HBFB, aqueous, concentrated bromate (non‐toxic, and stable) is reduced to bromide by a six‐electron process. 100 % conversion of BrO3− to Br− can be achieved. Although acidification of the BrO3− electrolyte is a prerequisite, the acid concentration in the electrolyte feed can be optimized as a trade‐off between area specific power (P) of the HBFB and its complexity.

Electrochemically driven evolution of Br-containing aqueous solution composition

“…These theoretical predictions on the ability of the redox cycle based on reactions (1a) and (2a) to provide very high discharge current densities were confirmed experimentally for the RDE [13] and microelectrode [14] configurations as well as for the hydrogen-bromate discharge cell [15] The next requirement for applications of bromates in flow batteries is to ensure the backward transformation of the discharge product, bromide solution, into the starting oxidant, bromate, preferably via electrolysis. Experimental examples of the Brelectrooxidation leading to formation of BrO3have been described in literature [16][17][18][19].…”

“…Such studies of electrochemical properties of the Br-containing system represent a vivid interest in relation to redox flow batteries, a rapidly developing type of electrochemical energy sources, based on bromine, Br2 (more precisely, on tribromide, Br3 -, in view of the limited solubility of Br2 in water, see below) or bromate, BrO3 -, ions as cathodic reagents [7,10,15,[29][30][31][32][33]. The information on the composition of such solutions as a function of the potential or of their total redox charge is of importance for description of processes both in their discharge devices and also in their regeneration reactors where the products of the discharge process are to be transformed back to the corresponding reagents electrochemically.…”

A Newly Designed Modular ZnBr2 Single Cell Structure

“…For every capacity, we perform three charge-discharge tests and calculate the average. As we know, energy efficiency characterizes the degree of recovery of stored energy, while voltage efficiency (VE) reflects the internal resistance of the cell, moreover, a high Coulomb efficiency (CE), which is related with electrodes' reversibility during the charge-discharge reaction process, indicates that the composite titanium-carbon felt electrodes have high conductivity and stability [22,23].…”

Novel Aqueous Zinc–Halogenate Flow Batteries as an Offspring of Zinc–Air Fuel Cells for Use in Oxygen‐Deficient Environment

“…A single cell of this H 2 /NaBrO 3 flow battery (HBFB) was constructed and tested. [ 27,28 ] Membrane electrode assembly (MEA) of the single cell consisted of hydrogen oxidation gas diffusion anode, Nafion cation‐exchange membrane, separating the electrodes, and a porous carbon felt flow through cathode, at which NaBrO 3 dissolved in acidified aqueous electrolyte was reduced to bromide in a six‐electron process. The HBFB can be considered as a spin‐off of hydrogen/air fuel cell in which aqueous bromate solution is used in place of gaseous oxygen.…”

“…The area‐specific power of the cell ( P ) with 50 cm 2 MEA reached 0.85 W cm −2 . [ 27 ] Estimated energy density per reactants of the HBFB flow cell was determined mostly by the energy density of hydrogen in a high‐pressure cylinder.…”