Rechargeable Oxide Batteries: Kinetic Study of Iron-Based Storage Materials in Low pO2-(H2O-Vapour)-Atmosphere

The transition from conventional fossil energy sources to renewable energies, known under the term “Energiewende” is in strong focus, not only in Germany but also in numerous other European countries and worldwide [1]. Therefore, energy sources are well known, such as: wind-, solar-, water-, and biomass power, which offers a possibility to satisfy the demand for renewable energy forms.

Public discussion often reduces the term “Energiewende” to the sector electricity which covers about 31 % of the actual energy production in Germany [2]. However, Germany’s goal is to balance at least 60 % of gross end energy consumption through renewable energy by 2050 [3].

For this purpose, we are faced to the fact to develop appropriate energy storage technologies, in order to obtain a decentralized and centralized power supply, allowing us to stabilize and compensate for the volatile availability of regenerative power plants.

As a novel concept high-temperature-metal-metaloxide storage systems (known as Rechargeable Oxide Battery (ROB)) were developed and examined (figure 1). The specific storage density is comparable to that of Li- or Na-S batteries and significantly higher than that of common lithium-ion batteries.

ROB storage materials imply a high volumetric energy density (= 3,04 Wh/) and therefore, offer great potential for application in the field of energy storage [4]. For this reason, the present work gives a fresh view on kinetic studies that illuminate particular redox-properties of selected Fe-based alloys (e. g. Fe-Y₂O₃, Fe-Al₂O₃, Fe-CaO) with respect to the H₂-formation/consumption. These specific properties were detected by mass spectrometry (MS). The MS-measurements are accompanied by thermogravimetric (TG) and differential thermal analytic (DTA) methods; the aim being to acquire a better understanding of typical Fe-reaction (to wustite, hematite, and iodestone) in a simulated low pO₂- atmosphere (Ar/4%H₂/7%H₂O) combined with a high temperature environment of 600-1000 °C. The composition and morphologies of the oxide scales were analyzed by optical metallography (OM), scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM/EDX), and X-ray diffraction (XRD).

In particular, the redox cyclability of the selected storage media plays an essential role in the charge and discharge behavior of a ROB. In this context, our studies present results of cycling experiments (n = 5-10) which show redox-responding behavior of the investigated materials and provide evidence towards the long term stability.

Literature:

[1] Benjamin Biegel, Lars Henrik Hansen, Jakob Stoustrup, Palle Andersen, Silas Harbo, Value of flexible consumption in the electricity markets. Energy 66, 354-362, 2014.

[2] Bruno Burger, public report, Frauenhofer Institut für Solar- und Energiesysteme (ISE), 09.10.2014. (http://www.ise.fraunhofer.de/, last status: 25.11.2014)

[3] Thomas Klaus, Carla Vollmer, Kathrin Werner, Harry Lehmann, Klaus Müschen, Energieziel 2050, Umweltbundesamt, 2010.

[4] H. Landes, R. Reichenbacher, Enhancement of Oxygen Transport in the Storage Electrode of a High Temperature Secondary Metal-Air Battery Based on an Oxygen Ion Conducting Electrolyte, ECS Transactions, 50 (25) 47-68 (2013).