(282e) A Mechanistic Insight into the Electrocatalytic Behavior of Mixed Oxide Cathode Catalysts for Li-O2 Batteries

The recent advancements in renewable energy generation will require investments in the development of energy storage technologies. Generally, the generated renewable energy can be stored in multiple forms, such as chemically (i.e., water splitting to form hydrogen fuel), mechanically (i.e., flywheel that converts electrical to rotational energy), or electrochemically (i.e., batteries that can store electrical energy). Among the many different electrochemical energy storage technologies, lithium-oxygen (Li-O₂) batteries exhibit the highest theoretical energy density (11,680 Wh/kg) [1]. Unlike the current state-of-the-art Li-ion batteries, where the technology has been explored for many years and reached a ceiling performance, Li-O₂ batteries are still far from reaching the theoretical energy density, thus are still under wide investigation [2]. In order to improve the performance of these systems, a fundamental understanding of the reaction mechanism involved in both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during discharge and charge respectively, at the cathode of these systems is necessary. It is in part due to the reported discharge product, Li₂O₂, being a high bandgap insulator, thereby making the electron transfer during OER extremely challenging [1]. We have shown previously that the performance of the Li-O₂ battery cathodes can be improved upon addition of non-precious metal oxide catalysts, known as Ruddlesden-Popper (R-P) oxides [3]. To optimize the performance of these catalytic materials, a fundamental understanding of the mechanism that leads to this improvement is required. In this contribution, we combine electrochemical and spectroscopic techniques to unravel the complex chemistry involved in Li-O₂ cathodes containing R-P oxide electrocatalysts. The effect of the nature of the discharged product species during ORR and its effect on lowering the overpotential losses during OER will be discussed. We finalize by devising ways of enhancing the performance of R-P oxides for oxygen reduction and evolution in Li-O₂ batteries.

References

1. Girishkumar, G., et al., Lithium - Air Battery: Promise and Challenges. Journal of Physical Chemistry Letters, 2010. 1(14): p. 2193-2203.

2. Armand, M. and J.M. Tarascon, Building better batteries. Nature, 2008. 451(7179): p. 652-657.

3. Nacy, A., X.F. Ma, and E. Nikolla, Nanostructured Nickelate Oxides as Efficient and Stable Cathode Electrocatalysts for Li-O-2 Batteries. Topics in Catalysis, 2015. 58(7-9): p. 513-521.