Abstract

Redox flow batteries (RFBs) enable large-scale energy storage at low cost due to the independent scaling of device power and energy, thereby unlocking energy arbitrage opportunities and providing a pathway to grid stability and resiliency. Currently, all-vanadium (all-V) RFBs, the only type of RFB which has been commercialized, is facing challenges (e.g., high material cost and low thermodynamic potential) that limit its application. Thus, it is critical to explore the applicability of combination between other redox couples. Furthermore, low energy efficiency (EE) and low capacity (by solubility limitation) are common issues in inorganic RFBs. This dissertation targets on the development of a new RFB system: Titanium (Ti)-Cerium (Ce) RFB. The promising standard potential difference between Ti and Ce couples (1.61 V vs. standard hydrogen electrode, SHE), large abundance of Ti and Ce, and the corresponding cost-effective nature of raw material build up the preconditions for this idea. A highly perm-selective modified poly(ether ketone)-based anion exchange membrane (AEM) is utilized as the separator which ensures long-term operation. The Ti-Ce RFB is tested with both sulfuric acid (H2SO4) and methanesulfonic acid (MSA) supporting electrolytes. In H2SO4, the battery is cycled at 100 mA cm-2 for over 1300 hours with negligible capacity fade and an average EE of 70%. In MSA, the electrolytes exhibit negligible self-discharge after being charged to 90% state of charge (SOC) and stored for 96 hours. After developing the baseline of Ti-Ce RFBs, the second task of this dissertation is performing electrode engineering for MSA-based electrolytes since MSA enables a higher solubility compared to H2SO4 (0.9 vs. 0.5 M). Exploiting the significant difference in reaction kinetics between the Ti and Ce actives, the interfacial area and surface functionalization (affecting electrode-electrolyte contact angles and charge transfer kinetics) of the electrode are optimized to increase operating power while reducing overall cell resistance. An asymmetric electrode configuration which applies carbon paper (CP) and carbon felt (CF) as electrodes of Ce and Ti side, respectively, results in increasing operating current density from 100 to 150 mA cm-2 while sustaining ~70% EE over 80 hours and 100 cycles. The third part of this dissertation is breaking the solubility limit of Ce in traditional acidic supporting electrolytes. Ammonium sulfate (AS) is applied as the supporting electrolyte to enable a supersaturated Ce(IV) electrolyte whose solubility is enhanced to 1.23 M by optimizing the ratio between Ce salt and AS. The study of solution chemistry from characterization techniques and theoretical calculation reveals that the key factor leading to this supersaturated solution is a synergistic effect of Ce(IV) hydrolysis with water and complexation with bisulfate ions (HSO4-). The utilization of AS supporting electrolyte makes Ti-Ce RFBs even more cost-effective, and the EE is stabilized over 70% at 50 mA cm-2.

Committee Chair

Vijay Ramani

Committee Members

Rohan Mishra; Shrihari Sankarasubramanian; Venkateshkumar Prabhakaran; Xinhua Liang; Zhen (Jason) He

Degree

Doctor of Philosophy (PhD)

Author's Department

Energy, Environmental & Chemical Engineering

Author's School

McKelvey School of Engineering

Document Type

Dissertation

Date of Award

11-11-2025

Language

English (en)

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Available for download on Sunday, November 07, 2027

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