Fired brick is a universal building material, produced by thousand-year-old technology, that throughout history has seldom served any other purpose. Here, we develop a scalable, costeffective and versatile chemical synthesis using a fired brick to control oxidative radical polymerization and deposition of a nanofibrillar coating of the conducting polymer poly(3,4ethylenedioxythiophene) (PEDOT). A fired brick's open microstructure, mechanical robustness and~8 wt% α-Fe 2 O 3 content afford an ideal substrate for developing electrochemical PEDOT electrodes and stationary supercapacitors that readily stack into modules. Fiveminute epoxy serves as a waterproof case enabling the operation of our supercapacitors while submerged underwater and a gel electrolyte extends cycling stability to 10,000 cycles with~90% capacitance retention.

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Increasing capacitance and energy density is a major challenge in developing supercapacitors for flexible portable electronics. A thick electrode with a high mass loading of active electronic material leads to high areal capacitance; however, the higher the loading, the higher the mechanical stiffness and ion diffusion resistance, thereby hampering development of flexible supercapacitors. Here, we show a chemical strategy that leads to a hierarchical electrode structure producing devices with both an exceedingly high areal capacitance and superior flexibility. We utilize α-Fe2O3 particles as an oxidant precursor for controlling oxidative radical polymerization of the conducting polymer poly­(3,4-ethylenedioxythiophene) (PEDOT) from the vapor phase. Our approach impregnates carbon cloth with α-Fe2O3 particles prior to monomer vapor exposure, resulting in state-of-the-art flexible nanofibrillar PEDOT supercapacitors possessing high areal capacitance (2243 mF/cm2 for two-electrode vs 6210 mF/cm2 for three-electrode) and high areal energy density (412 μWh/cm2).

Microsupercapacitors (µSCs) are attractive electrochemical energy storage devices serving as alternatives to batteries in miniaturized portable electronics owing to high‐power density and extended cycling stability. Current state‐of‐the‐art microfabrication strategies are limited by costly steps producing materials with structural defects that lead to low energy density. This paper introduces an electrode engineering platform that combines conventional microfabrication and polymerization from the vapor phase producing 3D µSCs of the conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT). A sputtered Fe2O3 precursor layer enables deposition of a 250 nm thick polymer coating comprised of a high packing density of vertically aligned PEDOT nanofibers possessing exceptional electrical conductivity (3580 S cm−1). The 3D µSCs exhibit state‐of‐the‐art volumetric energy density (16.1 mWh cm−3) as well as areal (21.3 mF cm−2) and volumetric (400 F cm−3) capacitances in 1 m H2SO4 aqueous electrolyte. These figures of merit represent the highest values among conducting polymer‐based µSCs. Electrochemical performance is controlled by investigating coating thickness, gap distance, fractal geometry, and gel electrolyte (1 m H2SO4/polyvinyl alcohol). The quasisolid‐state µSCs exhibit extended rate capability (50 V s−1), retain 94% of original capacitance after 10 000 cycles and remain thermally stable up to 60 °C.

Current state-of-the-art synthetic strategies produce conducting polymers suffering from low processability and unstable chemical and/or physical properties stifling research and development. Here, we introduce a platform for synthesizing scalable submicron-sized particles of the conducting polymer poly­(3,4-ethylenedioxythiophene) (PEDOT). The synthesis is based on a hybrid approach utilizing an aerosol of aqueous oxidant droplets and monomer vapor to engineer a scalable synthetic scheme. This aerosol vapor polymerization technology results in bulk quantities of discrete solid-state submicron particles (750 nm diameter) with the highest reported particle conductivity (330 ± 70 S/cm) so far. Moreover, particles are dispersible in organics and water, obviating the need for surfactants, and remain electrically conductive and doped over a period of months. This enhanced processability and environmental stability enable their incorporation in thermoplastic and cementitious composites for engineering chemoresistive pH and temperature sensors.