Improving the stability and discharge capacity of nanostructured Fe2O3/C anodes for iron-air batteries and investigation of 1-octhanethiol as an electrolyte additive

Iron-based aqueous batteries, such as the iron-air and nickel-iron chemistries, are limited by passivation and hydrogen evolution at the iron anode, especially at high current densities. In this paper, strategies to minimise these issues are investigated with iron electrodes composed of 20–50 nm Fe2O3 nanoparticles produced by the Adams and Oxalate methods. The strategies include ball milling the Fe2O3 with Ketjenblack carbon to improve conductivity, addition of bismuth sulphide to the electrode and 1-octanethiol to the electrolyte, and addition of potassium carbonate as a pore-forming agent. The ratio of Fe/C in the electrode and the 1-octanethiol additive have the greatest impact on the electrode capacity. The Fe/C ratio should be below 2.0 to ensure conductivity of the discharged electrode. The presence of 1-octanethiol can protect the electrodes from passivation during discharge; at very high 2C discharge rates adding 1-octanethiol increases the electrode specific capacity from 17 to 171 mAh/gFe. The synthesis method and use of pore former do not have a significant effect on the capacity. In all electrodes, the Fe2O3 nanoparticles are in the same crystalline phase after cycling and do not undergo significant crystal growth and passivation, demonstrating the stability and suitability of these materials for iron-based batteries. 3D image of experimental configuration (iron electrode versus a nickel counter electrode), with SEM image of electrode surface, and polarisation curves showing the discharge potential of the electrode in 6 mol dm−3 electrolyte with and without the presence of 0.1 mol dm−3 1-octanethiol additive. [Display omitted] •Effect of Fe/C ratio, synthesis method, and additives on Fe2O3 electrodes.•The best ratio was Fe/C = 2.0, allowing a compact, dense electrode.•Synthesis methods gave capacities >900 mAhg−1Fe higher than previously reported.•Electrodes showed none of the structural changes caused by passivation.•1-octanethiol additive increased the capacity more than tenfold at the 2C rate.