Design, construction and characterisation of an iron air battery for automotive propulsion

Novel energy storage technologies are required to further the development of crucial applications to reduce the dependence on fossil fuels. In particular for electric propulsion and for the efficient utilization of intermittent sources of renewable energy. Metal-air-batteries are appealing candidates to develop these type of energy-storage-technologies due to their theoretical energy-density. In particular the iron-air-battery (IAB) with a theoretical energy-density of 764 W h kg⁻¹, represents a low cost, environmentally friendly alternative. During the 70s, research into the IAB system was performed and a few laboratory prototypes were developed. Unfortunately, the specific energy density and cell potential of these prototypes were far below their theoretical value due to challenges in their engineering design and electrochemistry performance. Recently, the study of IABs has been of special interest to the automotive industry, due to the possibility of rechargeable metal-air batteries for electric vehicles. Furthermore, the new technological advances in nanomaterials since the 70s, and the use of new catalyst materials in combination with innovative laboratory tools for the manufacturing of the electrodes have enabled IAB s to achieve a further level of development. The main research goal of this Ph.D. research has been to determine the electrochemical performance of a novel IAB using novel nanostructured materials reported in the literature and to gain insight of what are the advantages and main challenges of this electrochemical system. The applied methodology included to develop and optimise each one of its components, mainly the negative iron-electrode, and the positive bifunctional-gas diffusion-electrode. The detailed study of the iron-electrode lead to the comparison of various reported active-iron-materials including: carbonyl iron, hematite, goethite, magnetite and iron sulphide as active-materials in hot-pressed-ironelectrodes, this research lead to the development of iron-electrodes with capacities as high as 910 m A g⁻¹ Fe using Fe₂O₃/C, and mean discharge capacities of 650 m A g ⁻¹ Fe over 240 hrs of continuous reduction-oxidation cycling at the C/5 rate (254.6 mA g⁻¹ Fe). Research on the air electrode lead to the development of a gas diffusion electrode with a remarkably stability able to cycle up to 3000 cycles continuously and to perform at current densities up to 1000 mA cm⁻² before deteriorating. Furthermore, the comparison of Ni-Fe hex-cyanoferrate, palladium and LSFCO perovskite on carbon as bifunctional catalysts and its combination lead to the development of optimised gas diffusion electrodes. In parallel the development as a proof of concept of an IAB stack and a larger scale IAB (200cm² GDE electrodes) required the engineering design of various IAB prototypes which were manufactured using 3D printing techniques that allowed rapid modifications and improvements before an optimised prototype was sent to be manufactured using traditional computer numerical control machining. The electrochemical testing of these batteries prototypes are as well part of the main results of this research. Finally, the electrochemical performance of a novel iron air battery prototype with an energy density as high as 453 W h kg⁻¹ Fe and a maximum capacity of 814 mA h g ⁻¹ Fe when cycled at a current density of 10 mA cm⁻² equivalent to 100 mA g⁻¹ Fe, achieving a power density of ca. 75 W kg⁻¹ Fe was achieved.