Converting Iron Corrosion Product to Nanostructured Conducting Polymers: Synthetic Strategies and Applications

ConspectusIron corrosion product, commonly known as rust, forms from the chemical reaction between iron and oxygen in the presence of water. It is a heterogeneous solid-state material composed of multiple phases and is ubiquitous throughout the universe. Sixteen distinct phases of iron corrosion product exist naturally under different temperature, pH, and pressure. Rust species such as hematite (α- Fe2O3), maghemite (γ-Fe2O3), goethite (α-FeOOH), and lepidocrocite (γ- FeOOH), first documented ca. 800 BCE, make up the solid-state chemical family composed of iron oxides, oxyhydroxides, and hydroxides. On an anthropogenic scale, rust represents a persistent problem to all manner of engineering and industrial pursuits. Corrosion is gradual and nondiscriminatory, affecting iron structures of all shapes and sizes from bridges and buildings to pipelines and wires that necessitates considerable spending on rust prevention and removal techniques. The infamous "Rust Belt" is colloquially used to describe regions of the United States characterized by sharp industrial decline and evokes images of derelict steel factories rusted over from decades of disuse. Therefore, iron corrosion product is commonly regarded as a symptom of deterioration and a physical manifestation of neglect in the eyes of the public. Yet, invaluable scientific potential exists within this "waste" material.Rust is thermodynamically stable, inexpensive, easily processable, and an abundant source of ferric ions (Fe3+) and therefore serves as an attractive oxidative candidate for developing chemical reactions. The ferric ion, with a standard reduction potential of +0.77 V, is an oxidizing agent that is well-investigated in the syntheses of highly conductive conjugated polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy). Additionally, hydrolysis products of ferric ions form various nanostructures and provide diversified growing template for conducting polymers, including rod-shape akageneite (β-FeOOH), fiber-shape goethite (α-FeOOH), 2D sheet iron oxychloride (FeOCl), and spherical/cubic hematite (α-Fe2O3).In this Account, we introduce our unique synthetic strategies that involve rust and advance the state-of-the-art in chemical synthesis of nanostructured conducting polymers. We utilize products from rust, droplets with rust, and interfaces containing rust to synthesize nanostructured conducting polymer including rust-based vapor-phase polymerization (RVPP), aerosol vapor polymerization (AVP), and condensing vapor-phase polymerization (CVPP). Owing to the high conductivity and high surface area, nanostructured conducting polymers are emerging as hotspots for electrode materials in energy storage devices (i.e., supercapacitors) and solar cells. In the second part of this Account, we discuss how combining our unique synthetic strategies with conventional materials and fabrication techniques produces devices with high figure of merit performance. These devices include a brick supercapacitor as proof-of-concept energy storage masonry material, a 3D microsupercapacitor with a superior and low-cost electrode engineering strategy as well as high energy density larger than a thin-lithium battery, and a dye-sensitized solar cell with an efficiency superior to that of Pt with cost-effective fabrication.