High-Energy-Density Chelated Chromium Flow Battery Electrolyte at Neutral pH.

High-concentration operation of redox flow batteries (RFBs) is essential for increasing their energy-storage capacity, but non-acidic electrolytes struggle to achieve the high concentrations of metal ions dissolved in acid, limiting the development of energy-dense neutral pH electrolytes. We report neutral pH RFB operation of chromium 1,3-propylenediaminetetraacetate (CrPDTA) at concentrations of 1.2 M at room temperature and 1.

Isolation and Characterization of a Highly Reducing Aqueous Chromium(II) Complex.

The highly reducing Cr-(1,3-propylenediaminetetraacetate) (CrPDTA) complex (-1.1 V vs SHE) has been isolated from aqueous solution and the solid-state structure is described. The reduced CrPDTA complex is characterized by single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy, UV-vis spectroscopy, magnetic moment, and density functional theory calculations.

Evaluating aqueous flow battery electrolytes: a coordinated approach.

Here, we outline some basic pitfalls in the electrochemical investigation of aqueous metal complexes and advocate for the use of bulk electrolysis in redox flow cells for electrolyte analysis. We demonstrate the methods of operation and performance of a lab scale redox flow battery (RFB), which is assembled from unmodified, commercially available material and cycled with a vanadium electrolyte in order to provide a comparative baseline of expected performance. Common misconceptions about the thermodynamic window for water splitting are addressed and further express the need to develop next-generation aqueous redox flow battery electrolytes.