Converting Rust to PEDOT Nanofibers for Supercapacitors

Iron corrosion, a product from the chemical reaction between iron and oxygen in the presence of water and commonly referred to as rust, is a heterogeneous solid-state material composed of multiple phases that represent an abundant source of chemical waste. Here, we introduce a strategy that advances the state-of-the-art in chemical synthesis by demonstrating the usefulness of this ubiquitous inexpensive inorganic material for developing oxidative radical polymerizations. Rust, when treated with an acid, is an ideal source of Fe3+ ions affording an oxidation potential of 0.77 V for oxidizing thiophene-based moieties and producing conducting polymers characterized by long conjugation lengths. We develop fundamental knowledge and mechanistic understanding that enables the deposition of freestanding nanofibrillar films of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) via rust-based vapor-phase polymerization (RVPP). Our process takes place in a single step inside a sealed hydrothermal reactor when monomer vapor makes contact with a solid-state rust coating undergoing dissolution—this approach is scalable requiring only a rusted steel surface, acid vapor, and monomer vapor. Freestanding nanofibrillar PEDOT films delaminate from a steel substrate characterized by an electronic conductivity of 323 S cm–1 and high electrochemical stability; RVPP enables patterning of a film in situ during synthesis. RVPP–PEDOT films are engineered into supercapacitors resulting in devices that exhibit a state-of-the-art capacitance of 181 F g–1 at a current density of 3.5 A g–1 and retain 80% of their original capacitance after 38 000 cycles.