Titanium-Anthraquinone Material as a New Design Approach for Electrodes in Aqueous Rechargeable Batteries

The need for expanded energy storage motivates material development for scalable aqueous secondary batteries. The combination of transition metals with redox-active organics represents a new approach to functional material design. Here, we detail the synthesis of titanium(IV) 1,8-dihydroxyanthraquinone (Ti(1,8-DHAQ)2) as a novel redox-active material and demonstrate its use as a negative electrode in an aqueous battery. This one-pot synthesis results in amorphous micron-scale particles with titanium binding directly to the carbonyl feature as evidenced by scanning electron microscopy and infrared spectroscopy. When assembled in a coin cell with a lithium manganese oxide positive electrode, the active material can be electrochemically cycled with a charge density of 40 mAh/g at 1.1 V. This represents a new method of creating simple and scalable electrodes using metal-organic materials for versatile energy storage applications.</div

Realized potential as neutral pH flow batteries achieve high power densities

High power density operation of redox flow batteries (RFBs) is essential for lowering system costs, but until now, only acid-based chemistries have achieved such performance, primarily due to rapid membrane proton (H+) transport. Here, we report a neutral pH RFB using the highly reducing Cr-(1,3-propylenediaminetetraacetate) (CrPDTA) complex that achieves acid-like power performance while utilizing potassium ion (K+) transport. We investigate RFB resistance components and demonstrate the high and consistent K+ conductivity of the Fumasep E-620(K) membrane. When combined with a robust bismuth electrocatalyst, this membrane enables constant voltage efficiency operation of a CrPDTA|Fe(CN)6 RFB for 200 cycles. An optimized CrPDTA|Fe(CN)6 RFB, which combines a high cell potential with a low area-specific resistance (0.46 &Omega; cm2), demonstrates a maximum discharge power density of 1.63&nbsp;W cm&minus;2 and an average discharge power density over 500 mW cm&minus;2 while maintaining 80% round-trip energy efficiency cycling, which are records for non-acid-based RFBs. &nbsp;</p

O-O bond formation and the transition metal chemistry of [beta]-diketiminate, siloxide, and triamide ligands

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2012.In title on title-page, "[beta]" appears as the lower-case Greek letter. Cataloged from PDF version of thesis.Includes bibliographical references.The electrochemical splitting of water into hydrogen and oxygen has been proposed as an alternative means to store electrical energy. The limiting aspect of this reaction is the oxygen forming reaction, which can be catalyzed by transition metal species with varying degrees of efficiency. This thesis examines the characteristics of oxygen bonding that complicate the 0-0 bond formation reaction, and examines ligand platforms that can stabilize high valent metal oxo intermediates. Siloxide ligands were used to generate a series of 4-coordinate Cr, Mn, Fe, and Co complexes, but these could not support the corresponding high valent oxo species. Instead, a remarkably stable 4-coordinate Crv tetrasiloxide complex was isolated. Chelating triamide ligands were explored, which might generate pseudotetrahedral metal oxo species, but complexes of various metal ions could not be reliably isolated. Planar bis-pdiketiminate (NacNac) complexes were synthesized by reaction of acetonitrile with Fe and Co mesityl species. The Co complex undergoes a ligand centered oxidation event to yield the first structurally characterized NacNac radical cation. In contrast to known redox noninnocent ligand platforms, no significant changes in C-C or C-N bond lengths are observed by X-ray crystallography. DFT calculations and the electronic and structural characterization of the oxidized and reduced Co complex confirm these conclusions.by Michael Pesek Marshak.Ph.D