Yifan Diao’s research while affiliated with Washington University in St. Louis and other places

Lack of solution processability is the main bottleneck in research progression and commercialization of conducting polymers. The current strategy of employing a water-soluble dopant (such as PEDOT:PSS) is not feasible with organic solvents, thus limiting compatibility on hydrophobic surfaces, such as three-dimensional (3D) printable thermoplastics. In this article, we utilize a colloidal dispersion of PEDOT particles to overcome this limitation and formulate an organic paint demonstrating conformal coating on 3D-printed objects. We start with synthesizing PEDOT particles that possess a low electrical resistance (gap resistance of 4.2 ± 0.5 Ω/mm). A particle-based organic paint is formulated and applied via brush painting. Coated objects show a surface resistance of 1 kΩ/cm, comparable to an object printed by commercial conductive filaments. The coating enables the fabrication of pH and strain sensors. Highly conductive PEDOT particles also absorb light strongly, especially in the near-infrared (NIR) range due to the high concentration of charge carriers on the polymer's conjugated backbones (i.e., polarons and bipolarons). PEDOT converts light to heat efficiently, resulting in a superior photothermal activity that is demonstrated by the flash ignition of a particle-impregnated cotton ball. Consequently, painted 3D prints are highly effective in converting NIR light to heat, and a 5 s exposure to a NIR laser (808 nm, 0.8 mW/cm2) leads to a record high-temperature increase (194.5 °C) among PEDOT-based coatings.

Atmospheric pollution demands the development of solar-driven photocatalytic technologies for the conversion of CO2 into a fuel; state-of-the-art cocatalyst systems demonstrate conversion efficiencies currently unattainable by a single catalyst. Here, we upend the status quo demonstrating that the nanofibrillar conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is a record-breaking single catalyst for the photoreduction of CO2 to CO. This high catalytic efficiency stems from a highly conductive nanofibrillar structure that significantly enhances surface area, CO2 adsorption and light absorption. Moreover, the polymer’s band gap is optimized via chemical doping/dedoping treatments using hydrochloric acid, ammonia hydroxide, and hydrazine. The hydrazine-treated PEDOT catalyst exhibits 100% CO yield under a stable regime (>10 h) with a maximum rate of CO evolution (3000 μmol gcat–1 h–1) that is 2 orders of magnitude higher than the top performing single catalyst and surpassed only by three other cocatalyst systems. Nanofibrillar PEDOT provides a new direction for designing the next generation of high-efficiency photoreduction catalysts.

Organometallic halide perovskite (MAPPbBr3), Rust-based Vapor Phase Polymerization (RVPP)-PEDOT hole transporting layers and (RVPP-PEDOT)/MAPPbBr3 dual-layer, deposited on fluorine doped tin oxide glass were studied at room temperature using steady-state absorption, time-resolved photoluminescence imaging and femtosecond time-resolved absorption spectroscopy. Application of these techniques in conjunction with diverse excitation intensities allowed determination of various optoelectronic properties of the perovskite film and the time constant of the hole extraction process. Spectral reconstruction of the bandedge absorption spectrum using Elliot's formula enabled separation of the exciton band. The binding energy of the exciton was determined to be 19 meV and the bandgap energy of the perovskite film was 2.37 eV. Subsequent time-resolved photoluminescence studies of the perovskite film performed using a very weak excitation intensity followed by a global analysis of the data revealed monomolecular recombination dynamics of charge carriers occurring with an amplitude weighted lifetime of 3.2 ns. Femtosecond time-resolved transient absorption of the film performed after excitation intensity spanning a range of over two orders of magnitude enabled determining the rate constant of bimolecular recombination and was found to be 2.6 × 10-10 cm3 s-1. Application of numerous high intensity excitations enabled observation of band filling effect and application of the Burstein-Moss model allowed to determine the reduced effective mass of photoexcited electron-hole pair in MAPPbBr3 film to be 0.19 rest mass of the electron. Finally, application of transient absorption on RVPP-PEDOT/MAPPbBr3 enabled determination of a 0.4 ps time constant for the MAPPbBr3-to-PEDOT hole extraction process.

Kirigami, the art of paper cutting, presents a promising approach for maximizing stretchability in planar sheets which is of paramount importance for the next-generation of wearable smart electronics. Current state-of-the-art Kirigami-based devices suffer from thin-film electrodes characterized by a limited surface area and poor electronic performance. Here, we introduce a synthetic strategy that affords layer-by-layer control for depositing nanofibrillar conducting polymer composite coatings possessing a high packing density and high surface area. A Kirigami-based humidity dosimeter developed using our PEDOT nanofibers exhibits superior sensitivity over the commercial product PEDOT:PSS. This wearable dosimeter, when stretched by 200%, exhibits a 40% resistance change within seconds (<2 s) after exposure to a new humidity level. A PPy/PEDOT composite film is produced by sequential deposition of two different conducting polymer nanofibers resulting in a superior electrode for developing stretchable supercapacitors. Our electrochemical capacitors exhibit a synergistic effect that leads to a state-of-the-art energy density (115 μW h cm⁻²at 1 mA cm⁻²) and an extended stretch cycle capacitance stability (85% of original capacitance is retained after 300 stretching cycles of 100%).

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).

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, cost-effective and versatile chemical synthesis using a fired brick to control oxidative radical polymerization and deposition of a nanofibrillar coating of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). A fired brick’s open microstructure, mechanical robustness and ~8 wt% α-Fe2O3 content afford an ideal substrate for developing electrochemical PEDOT electrodes and stationary supercapacitors that readily stack into modules. Five-minute 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. Fired brick is a universal building material, produced by thousand-year-old technology, which throughout history has seldom served any other purpose. Here, the authors show that bricks can store energy after chemical treatment to convert their iron oxide content into conducting polymer nanofibers.

Microsupercapacitors (μSCs) are electrochemical energy storage devices serving as alternatives to batteries in miniaturized portable electronics. In article number 2003394, Julio M. D'Arcy and co‐workers demonstrate a superior and cost‐effective route for developing 3D μSCs that directly convert Fe2O3 to poly(3,4‐ethylenedioxythiophene) (PEDOT) nanofibers in one step. A vertically aligned PEDOT electrode possesses exceptional conductivity (3580 S cm−1) and results in a device exhibiting one of the highest energy densities (400 F cm−3) reported among organic μSCs.

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.