Influence of Ligands on the Cu(I/II) Redox Reaction for Redox Flow Batteries

Abstract

For meeting ambitious carbon-free electricity goals, low-cost electrical energy storage solutions are needed. Although redox flow batteries are a promising option to satisfy this need, the cost of these devices must decrease before widespread adoption can take place. As the electrolytes are the most significant expense for MW-scale flow batteries, new chemistries derived from inexpensive metals is one approach that may alleviate this bottleneck towards a carbon-free power grid. Here we use an electrochemical approach by applying a rotating disc electrode (RDE) to quantify how ligand chemistries can favorably manipulate the electrochemical parameters of the Cu(I/II) redox reaction, progressing these chemistries forward as potential low-cost electrolytes for redox flow batteries. In this research, multiple ligands were used to analyze such impacts on aqueous copper metal complexes by using both a platinum and carbon tipped electrode installed into the RDE. Electrochemical Impedance Spectroscopy (EIS), Linear Sweep Voltammetry (LSV) and Open Circuit Potential (OCP) were the three techniques utilized to analyze the effects of these metal complexes. The experimental data was analyzed using the Butler-Volmer and Nernst equations. As step reactions are mostly unknown for these reactions, LSV and EIS data gave insights into what may be occurring at the electrode interfaces. OCP data quantified how different ligands modified the standard electrode potentials of the Cu(I/II) redox reaction.