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

Conspectus Iron corrosion product, commonlyknown as rust, forms from thechemical reaction between iron and oxygen in the presence of water.It is a heterogeneous solid-state material composed of multiple phasesand is ubiquitous throughout the universe. Sixteen distinct phasesof iron corrosion product exist naturally under different temperature,pH, and pressure. Rust species such as hematite (& alpha;- Fe2O3), maghemite (& gamma;-Fe2O3),goethite (& alpha;-FeOOH), and lepidocrocite (& gamma;- FeOOH), firstdocumented ca. 800 BCE, make up the solid-state chemical family composedof iron oxides, oxyhydroxides, and hydroxides. On an anthropogenicscale, rust represents a persistent problem to all manner of engineeringand industrial pursuits. Corrosion is gradual and nondiscriminatory,affecting iron structures of all shapes and sizes from bridges andbuildings to pipelines and wires that necessitates considerable spendingon rust prevention and removal techniques. The infamous "RustBelt" is colloquially used to describe regions of the UnitedStates characterized by sharp industrial decline and evokes imagesof derelict steel factories rusted over from decades of disuse. Therefore,iron corrosion product is commonly regarded as a symptom of deteriorationand 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, easilyprocessable,and an abundant source of ferric ions (Fe3+) and thereforeserves as an attractive oxidative candidate for developing chemicalreactions. The ferric ion, with a standard reduction potential of+0.77 V, is an oxidizing agent that is well-investigated in the synthesesof highly conductive conjugated polymers such as poly(3,4-ethylenedioxythiophene)(PEDOT) and polypyrrole (PPy). Additionally, hydrolysis products offerric ions form various nanostructures and provide diversified growingtemplate for conducting polymers, including rod-shape akageneite (& beta;-FeOOH),fiber-shape goethite (& alpha;-FeOOH), 2D sheet iron oxychloride (FeOCl),and spherical/cubic hematite (& alpha;-Fe2O3). In this Account, we introduce our unique synthetic strategies thatinvolve rust and advance the state-of-the-art in chemical synthesisof nanostructured conducting polymers. We utilize products from rust,droplets with rust, and interfaces containing rust to synthesize nanostructuredconducting polymer including rust-based vapor-phase polymerization(RVPP), aerosol vapor polymerization (AVP), and condensing vapor-phasepolymerization (CVPP). Owing to the high conductivity and high surfacearea, nanostructured conducting polymers are emerging as hotspotsfor electrode materials in energy storage devices (i.e., supercapacitors)and solar cells. In the second part of this Account, we discuss howcombining our unique synthetic strategies with conventional materialsand fabrication techniques produces devices with high figure of meritperformance. These devices include a brick supercapacitor as proof-of-conceptenergy storage masonry material, a 3D microsupercapacitor with a superiorand low-cost electrode engineering strategy as well as high energydensity larger than a thin-lithium battery, and a dye-sensitized solarcell with an efficiency superior to that of Pt with cost-effectivefabrication.