(84az) Stability and Redox Kinetics of Ti4+/Ti3+ for Flow Battery Applications

Interest in understanding and improving titanium redox kinetics has surfaced as titanium-based anolytes are explored for energy storage applications. Technologies that harness renewable energy have decreased in cost, creating a demand for viable energy storage technologies that are compatible with intermittent sources¹. To be practical, the production and storage/transmission/distribution of this energy must be less expensive than fossil-based alternatives. Flow batteries can be suitable for long-duration and intermittent storage with the unique benefit of scaling power and energy independently^1,2. The most developed and mature flow battery is the all-vanadium redox flow battery (RFB). While this technology has undergone commercial production, it is not yet widely available due to high cost, driven by the expense of vanadium itself¹. There have been several alternative RFB chemistries proposed that utilize titanium-based anolytes paired with various catholytes such as cerium and manganese^2,3. For the titanium-cerium system, preliminary cycling data shows minimal coulombic efficiency fade but relatively modest energy efficiency (< 70%) at current densities of 150 mA/cm² due to kinetic limitations. From comparing the rate constants of the two redox couples (TiO²⁺/Ti³⁺ and Ce³⁺/Ce⁴⁺) in methanesulfonic acid, the titanium rate constant is three orders of magnitude lower than that of cerium. The addition of Mn²⁺ ions has been explored to improve titanium kinetics in sulfuric acid for a titanium-manganese RFB, but reported no kinetic effects³. Both these chemistries are limited by the research gap surrounding titanium redox kinetics. Herein we report experimentally observed titanium redox kinetics with methanesulfonic acid and with sulfuric acid supporting electrolytes. We demonstrate the transient stability of these electrolytes via both electrochemical behavior and spectroscopic shifts. Understanding the kinetics of the titanium redox reaction will pave the way to make further advancements in titanium anolyte RFB systems.

References:

[1] Gü, T. M. (2018). Review of electrical energy storage technologies, materials and systems: challenges and prospects for large-scale grid storage. 2696 | Energy Environ. Sci, 11, 2696. https://doi.org/10.1039/c8ee01419a

[2] Shrihari Sankarasubramanian, Yunzhu Zhang, Cheng He et al. An Aqueous, Electrode-Decoupled Redox-Flow Battery for Long Duration Energy Storage, 27 January 2021, PREPRINT (Version 1) available at Research Square [https://doi.org/10.21203/rs.3.rs-150474/v1]

[3] Dong, Y., Kaku, H., Miyawaki, H., Tatsumi, R., Moriuchi, K., & Shigematsu, T. (2017). Titanium-Manganese Electrolyte for Redox Flow Battery. SEI TECHNICAL REVIEW, 84, 35–40.