Abstract
Iron is abundant, low-cost, environmentally benign, and non-toxic element. Its magnetic and electrochemical properties make this metal a promising material for various applications. This dissertation explores the use of iron and iron containing compounds in aqueous energy storage and sensor applications.Battery storage technology can address a key limitation to renewable energy. As renewable electricity generation (solar and wind) is intermittent, they require power buffering. For large-scale use the requirements are that this energy storage device be safe and inexpensive. Energy storage systems that use aqueous electrolyte solvent are safer and provide cost reductions compared to cells with organic electrolytes. The studies presented in Chapters 2 and 3 utilize all iron chemistry that can be built safely in DIY setting. Both all-iron batteries use the Fe0,II oxidation states at the negative electrode and FeII,III at the positive. Chapter 2 highlights the significant improvements to ‘open-source all-iron battery for renewable energy storage’. The original iron chemistry was simplified and showed more reproducible procedure for preparing electro-active materials. The addition of conductive carbon improved the current density by decreasing the distance between current collector and iron precipitate. The results are a highly rechargeable electrochemical cell based on iron, chloride, sulfate, and potassium ions in water at near-neutral pH. With modest volumetric capacity of 9.5 Ah/L the cell is able to deliver a maximal power of 250 mW/L. While its low cost, simple synthesis, and safe manufacturing may make it suitable for storing renewable energy, the power density is low for practical application. We sought to improve the power performance of all-iron battery by the use of redox mediators and improved electroactive material synthesis. These studies are discussed in chapter 3. The cell employs commodity chemicals methyl viologen (MV) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) at the iron anode and iron (III) cathode, respectively. The result is a highly rechargeable, low-cost energy storage system with a good price-performance ratio compared to commercial rechargeable batteries that is stable for 100+ cycles with 84% capacity retention. The cell has a volumetric capacity of 9.6 Ah/L (energy of 11.52 wh/L) but maximal power is increased more than an order magnitude to 3600 mW/L.
A lithium-ion sulfur battery concept is presented in Chapter 4. This is based on lithium ion intercalating into an iron-based compound at the positive electrode and a formation of lithium polysulfides from sulfur at the negative electrode. The combination of low cost and long life in this system enhances one or more of the following cell attributes: energy storage capacity per unit cost, power capacity per unit cost, and cycle life (and total amortized cost per cycle). The use of an aqueous electrolyte in combination with inexpensive sulfur as the active material can be a key enabler for the utility industries, for example, providing a cost-effective solution for load leveling and renewable energy storage. The battery has a volumetric capacity of 22.9 Ah/L and was stable for 1500+ cycles with more than 90% capacity retention.
Chapter 5 demonstrates a rapid and sensitive method for DNA detection without the need for fluorescence. This is based on carbon-coated magnetic iron (Fe) microparticles with a covalent surface attachment of DNA. We showed that these magnetic microparticles can capture complementary DNA. Significantly, the DNA covalent surface bonds are robust to high temperatures and can be included in a sample during polymerase chain reaction (PCR). This method is employed for the detection of targeted DNA sequences (40–50 bp). Hybridization probes on the surface of the magnetically susceptible Fe microparticle recognize the target DNA sequence-specifically. The double-stranded DNA (dsDNA) microparticles are then quickly captured with a magnet from the sample matrix. This foregoes post purification processes, such as electrophoresis, which make our technique time- and cost-effective. Captured dsDNA can be detected with intercalating dyes such as ethidium bromide through a loss in the UV absorption signal with a limit of detection (LOD) of 24 nM within 15 min. Likewise, surface-bound DNA can act as a primer in PCR to decrease the LOD to 5 pM within 2 h. This is the first instance of a nucleotide-modified magnetically susceptible carbon substrate that is PCR-compatible. Besides DNA capture, this strategy can eventually be applied to sequence-specific nucleic acid purification and enrichment, PCR cleanup, and single-strand generation. The DNA-coated particles are stable under PCR conditions (unlike commonly used polystyrene or gold particles).