Regenerating Iron via Electrolysis for CO2-Free Energy Storage and Carrier

To tackle the intermittency problem in renewable energy usage, it is necessary to develop sustainable energy storage and transportation technologies. One such solution is the use of iron powder as an energy carrier, which enables flexible energy usage. The combustion process releases the energy stored in iron powder while the solid product, i.e., iron oxide can be easily collected and then reduced to metallic iron, enforcing a recyclable iron fuel cycle (Fig.1). We investigate the use of electrochemical technique for iron regeneration in the context of the iron fuel cycle [1-4]. The laboratory-scale experiments with parallel plate electrolyzer using aqueous NaOH (50%wt, 18 M) suspended with micron-sized Fe2O3 (hematite) powder are conducted in the present work. We study the electrochemical performance and deposition behavior of the iron, exploring different parameters such as current density, iron oxide concentration, temperature, NaOH concentration, and powder size, with the aim of achieving optimal Faradaic efficiency. A high Faradaic efficiency (>90%) and high iron purity cathodic deposition have been achieved in relatively low electrical energy consumption (less than 6 kWh/kg). The metallic iron is deposited in the form of unique dendritic structures on the cathode. (Fig. 2). The dendrites are located primarily on the side and edge of the cathode, indicating a diffusion-controlled mechanism. This structure makes it easy for direct harvest of the iron powder. A new reactor design with a rotating disc as a cathode is proposed to realize continuous electrolytic iron powder production [4]. The obtained results open new perspectives for the completion of the iron fuel cycle, by enabling a sustainable regeneration of iron. References: [1] N.van Graefschepe, A.I. Majid, Y. Tang, G. Finotello, J.van der Schaaf, N.G. Deen. 2022. NPS 17 Delft. [2] A.I. Majid, N.van Graefschepe, Y. Tang, G. Finotello, J.van der Schaaf, N.G. Deen. 2022. 32nd ISE Topical Meeting. [3] A.I. Majid, N.van Graefschepe, Y. Tang, G. Finotello, J.van der Schaaf, N.G. Deen. 2022. In preparation. [4] A.I. Majid, Y. Tang, G. Finotello, J.van der Schaaf, N.G. Deen. 2022. US Provisional Patent, 63/363,627