Understanding the Impact of Ligand and State-of-charge on Electrolyte, Redox Reaction and Electrode Stability for the Cerium-based Flow Battery

Project: Research

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Redox flow batteries (RFBs) promise to solve one of the critical energy challenges toward sustainable development – efficient storage of renewable energy. Improving the concentration of the electrolyte is the most important approach to promote the energy density and capacity in a finite volume of the RFB, which can be obtained effectively by using an appropriate supporting electrolyte. Single and mixed acid media have been investigated in various RFBs, including zinc-cerium RFB, a battery with higher storage capacity than all vanadium RFB (VRFB). Methanesulfonic acid (MSA) is the most commonly used and favorable acid medium for cerium electrolyte. We have investigated mixed acid media of MSA with other inorganic acids and found that mixed acids of MSA and HCl can facilitate the redox reaction and contribute to better reversibility. However, there is absence of knowledge on the mechanism of cerium reaction in HCl solution. Whilst researchers have studied the cerium reaction in MSA, the improved solubility has not been explained, without such knowledge, systematic improvement of supporting electrolytes remains unattainable.Of particular interest here is the cerium ion with methanesulfonate ligand and mixed ligands of methanesulfonate and chloride, studied at glassy carbon surface (as a standard carbon material). It is known that many aspects of the reaction are improved in mixed ligands, but even at the well-studied glassy carbon there is no clear understanding of the interaction between electrode and electrolyte, which forms the foundation for further development.We propose therefore to gain a comprehensive understanding of the impact of ligands on the electrolyte and redox reaction, as well as the stability of electrode. Saturation ion product will be calculated, combining with the recorded time before precipitation, to assess the solubility and stability. Formal potential, reversibility, diffusion coefficient and reaction kinetics will be measured to study the role of ligands and concentrations, under a range of state-of-charge. Stability of the carbon material can be affected by the ligand, which will also be investigated by charge-discharge cycling at different temperatures. Conclusion drawn from the experiment will be explained in conjunction with density functional theory (DFT) calculations within the framework of electrocatalysis. Using the state-of-the-art DFT techniques, the complexation and activation energies of the large metal ion, Ce(III)/Ce(IV) will be gained. Each of the factors affecting the electrochemical reaction will be accounted for – the approach of the ion to the electrode, the reorganization of ligands and solvents, the double layer, the transfer of charge and the relaxation to the new equilibrium.The study presents a broad and accurate investigation of the RFB, which would explain the impact of ligand on the system. The approach taken here has the potential to be applied not only to other RFB but also to more general electrochemical situations. The study therefore would be a prototype of great benefit to the electrochemical field, such as application to other electrode materials, ions and other multi-step reactions.


Project number9042553
Effective start/end date1/01/18 → …