Low-Temperature Molten Salt Electrochemical CO2 Upcycling for Advanced Energy Materials.

One strategy for addressing the climate crisis caused by CO2 emissions is to efficiently convert CO2 to advanced materials suited for green and clean energy technology applications. Porous carbon is widely used as an advanced energy storage material because of its enhanced energy storage capabilities as an anode. Herein, we report electrochemical CO2 upcycling to solid carbon with a controlled microstructure and porosity in a ternary molten carbonate melt at 450 °C. Controlling the electrochemical parameters (voltage, temperature, cathode material) enabled the conversion of CO2 to porous carbon with a tunable morphology and porosity for the first time at such a low temperature. Additionally, a well-controlled morphology and porosity are beneficial for reversible energy storage. In fact, these carbon materials delivered high specific capacity, stable cycling performances, and exceptional rate capability even under extremely fast charging conditions when integrated as an anode in lithium-ion batteries (LIBs). The present approach not only demonstrated efficient upcycling of CO2 into porous carbon suitable for enhanced energy storage but can also contribute to a clean and green energy technology that can reduce carbon emissions to achieve sustainable energy goals.

Surface-modified and oven-dried microfibrillated cellulose reinforced biocomposites: Cellulose network enabled high performance.

Microfibrillated cellulose (MFC) is widely used as a reinforcement filler for biocomposites due to its unique properties. However, the challenge of drying MFC and the incompatibility between nanocellulose and polymer matrix still limits the mechanical performance of MFC-reinforced biocomposites. In this study, we used a water-based transesterification reaction to functionalize MFC and explored the capability of oven-dried MFC as a reinforcement filler for polylactic acid (PLA). Remarkably, this oven-dried, vinyl laurate-modified MFC improved the tensile strength by 38 % and Young's modulus by 71 % compared with neat PLA. Our results suggested improved compatibility and dispersion of the fibrils in PLA after modification. This study demonstrated that scalable water-based surface modification and subsequent straightforward oven drying could be a facile method for effectively drying cellulose nanomaterials. The method helps significantly disperse fibrils in polymers and enhances the mechanical properties of microfibrillar cellulose-reinforced biocomposites.

Hierarchical TiO2:Cu2O Nanostructures for Gas/Vapor Sensing and CO2 Sequestration.

We investigate the effect of high-surface-area self-assembled TiO2:Cu2O nanostructures for CO2 and relative humidity gravimetric detection using polyethylenimine (PEI), 1-ethyl-3-methylimidazolium (EMIM), and polyacrylamide (PAAm). Introduction of hierarchical TiO2:Cu2O nanostructures on the surface of quartz crystal microbalance sensors is found to significantly improve sensitivity to CO2 and to H2O vapor. The response of EMIM to CO2 increases fivefold for 100 nm-thick TiO2:Cu2O as compared to gold. At ambient CO2 concentrations, the hierarchical assembly operates as a sensor with excellent reversibility, while at higher pressures, the CO2 desorption rate decreases, suggesting possible application for CO2 sequestration under these conditions. The gravimetric response of PEI to CO2 increases by a factor of 3 upon introduction of a 50 nm TiO2:Cu2O layer. The PAAm gravimetric response to water vapor also increases by a factor of 3 and displays improved reversibility with the addition of 50 nm TiO2:Cu2O structures. We found that TiO2:Cu2O can be used to lower the detection limits for CO2 sensing with EMIM and PEI and lower the detection limits for H2O sensing with PAAm by over a factor of 2. Coarse-grained and all-atom molecular dynamics simulations indicate the dissociative character of ionic liquid assembly on TiO2:Cu2O interfaces and different distributions of CO2 and H2O molecules on bare and ionic liquid-coated surfaces, confirming experimental observations. Overall, our results show high potential of hierarchical assemblies of TiO2:Cu2O/room temperature ionic liquid and polymer films for sensors and CO2 sequestration.

Vacuum-Assisted Low-Temperature Synthesis of Reduced Graphene Oxide Thin-Film Electrodes for High-Performance Transparent and Flexible All-Solid-State Supercapacitors.

Simple and easily integrated design of flexible and transparent electrode materials affixed to polymer-based substrates hold great promise to have a revolutionary impact on the functionality and performance of energy storage devices for many future consumer electronics. Among these applications are touch sensors, roll-up displays, photovoltaic cells, health monitors, wireless sensors, and wearable communication devices. Here, we report an environmentally friendly, simple, and versatile approach to produce optically transparent and mechanically flexible all-solid-state supercapacitor devices. These supercapacitors were constructed on tin-doped indium oxide coated polyethylene terephthalate substrates by intercalation of a polymer-based gel electrolyte between two reduced graphene oxide (rGO) thin-film electrodes. The rGO electrodes were fabricated simply by drop-casting of graphene oxide (GO) films, followed by a novel low-temperature (≤250 °C) vacuum-assisted annealing approach for the in situ reduction of GO to rGO. A trade-off between the optical transparency and electrochemical performance is determined by the concentration of the GO in the initial dispersion, whereby the highest capacitance (∼650 µF cm-2) occurs at a relatively lower optical transmittance (24%). Notably, the all-solid-state supercapacitors demonstrated excellent mechanical flexibility with a capacity retention rate above 90% under various bending angles and cycles. These attributes underscore the potential of the present approach to provide a path toward the realization of thin-film-based supercapacitors as flexible and transparent energy storage devices for a variety of practical applications.

Low-Thermal-Budget Photonic Processing of Highly Conductive Cu Interconnects Based on CuO Nanoinks: Potential for Flexible Printed Electronics.

In the developing field of printed electronics, nanoparticle based inks such as CuO show great promise as a low-cost alternative to other metal-based counterparts (e.g., silver). In particular, CuO inks significantly eliminate the issue of particle oxidation before and during the sintering process that is prevalent in Cu-based formulations. We report here the scalable and low-thermal-budget photonic fabrication of Cu interconnects employing a roll-to-roll (R2R)-compatible pulse-thermal-processing (PTP) technique that enables phase reduction and subsequent sintering of ink-jet-printed CuO patterns onto flexible polymer templates. Detailed investigations of curing and sintering conditions were performed to understand the impact of PTP system conditions on the electrical performance of the Cu patterns. Specifically, the impact of energy and power of photonic pulses on print conductivity was systematically studied by varying the following key processing parameters: pulse intensity, duration, and sequence. Through optimization of such parameters, highly conductive prints were obtained in <1 s with resistivity values as low as 10 µΩ cm (corresponding to ∼17% of the International Annealed Copper Standard (IACS) conductivity) was achieved. It was also observed that the introduction of an initial ink-drying step in ambient atmosphere, after the printing and before sintering, leads to significant improvements in mechanical integrity and electrical performance of the printed Cu patterns. Moreover, the viability of CuO reactive inks, coupled with the PTP technology and pre-sintering ink-drying protocols, has also been demonstrated for the additive integration of a low-cost Cu temperature sensor onto a flexible polymer substrate.

Controllable Growth of Perovskite Films by Room-Temperature Air Exposure for Efficient Planar Heterojunction Photovoltaic Cells.

A two-step solution processing approach has been established to grow void-free perovskite films for low-cost high-performance planar heterojunction photovoltaic devices. A high-temperature thermal annealing treatment was applied to drive the diffusion of CH3NH3I precursor molecules into a compact PbI2 layer to form perovskite films. However, thermal annealing for extended periods led to degraded device performance owing to the defects generated by decomposition of perovskite into PbI2. A controllable layer-by-layer spin-coating method was used to grow "bilayer" CH3NH3I/PbI2 films, and then drive the interdiffusion between PbI2 and CH3NH3I layers by a simple air exposure at room temperature for making well-oriented, highly crystalline perovskite films without thermal annealing. This high degree of crystallinity resulted in a carrier diffusion length of ca. 800 nm and a high device efficiency of 15.6%, which is comparable to values reported for thermally annealed perovskite films.

Superhydrophobic materials and coatings: a review.

Over the past few years, the scientific community, as well as the world's coatings industry has seen the introduction of oxide/polymer-based superhydrophobic surfaces and coatings with exceptional water repellency. Online videos have caught the public's imagination by showing people walking through mud puddles without getting their tennis shoes wet or muddy, and water literally flying off coated surfaces. This article attempts to explain the basics of this behavior and to discuss and explain the latest superhydrophobic technological breakthroughs. Since superhydrophobic surfaces and coatings can fundamentally change how water interacts with surfaces, and the fact that earth is a water world, it can legitimately be said that this technology has the potential to literally change the world.

Plasmonic three-dimensional transparent conductor based on Al-doped zinc oxide-coated nanostructured glass using atomic layer deposition.

Transparent nanostructured glass coatings, fabricated on glass substrates, with a unique three-dimensional (3D) architecture were utilized as the foundation for designing plasmonic 3D transparent conductors. Transformation of the nonconducting 3D structure to a conducting porous surface network was accomplished through atomic layer deposition of aluminum-doped zinc oxide (AZO). After AZO growth, gold nanoparticles (AuNPs) were deposited by electron-beam evaporation to enhance light trapping and decrease the overall sheet resistance. Field emission scanning electron microscopy and atomic force microcopy images revealed the highly porous, nanostructured morphology of the AZO-coated glass surface along with the in-plane dimensions of the deposited AuNPs. Sheet resistance measurements conducted on the coated samples verified that the electrical properties of the 3D network are comparable to those of untextured two-dimensional AZO-coated glass substrates. In addition, transmittance measurements of the glass samples coated at various AZO thicknesses showed preservation of the transparent nature of each sample, and the AuNPs demonstrated enhanced light scattering as well as light-trapping capabilities.

Superhydrophobic ceramic coatings enabled by phase-separated nanostructured composite TiO2-Cu2O thin films.

By exploiting phase-separation in oxide materials, we present a simple and potentially low-cost approach to create exceptional superhydrophobicity in thin-film based coatings. By selecting the TiO2-Cu2O system and depositing through magnetron sputtering onto single crystal and metal templates, we demonstrate growth of nanostructured, chemically phase-segregated composite films. These coatings, after appropriate chemical surface modification, demonstrate a robust, non-wetting Cassie-Baxter state and yield an exceptional superhydrophobic performance, with water droplet contact angles reaching to ~172° and sliding angles <1°. As an added benefit, despite the photo-active nature of TiO2, the chemically coated composite film surfaces display UV stability and retain superhydrophobic attributes even after exposure to UV (275 nm) radiation for an extended period of time. The present approach could benefit a variety of outdoor applications of superhydrophobic coatings, especially for those where exposure to extreme atmospheric conditions is required.

Optically transparent, mechanically durable, nanostructured superhydrophobic surfaces enabled by spinodally phase-separated glass thin films.

We describe the formation and properties of atomically bonded, optical quality, nanostructured thin glass film coatings on glass plates, utilizing phase separation by spinodal decomposition in a sodium borosilicate glass system. Following deposition via magnetron sputtering, thermal processing and differential etching, these coatings are structurally superhydrophilic (i.e., display anti-fogging functionality) and demonstrate robust mechanical properties and superior abrasion resistance. After appropriate chemical surface modification, the surfaces display a stable, non-wetting Cassie-Baxter state and exhibit exceptional superhydrophobic performance, with water droplet contact angles as large as 172°. As an added benefit, in both superhydrophobic and superhydrophilic states these nanostructured surfaces can block ultraviolet radiation and can be engineered to be anti-reflective with broadband and omnidirectional transparency. Thus, the present approach could be tailored toward distinct coatings for numerous markets, such as residential windows, windshields, specialty optics, goggles, electronic and photovoltaic cover glasses, and optical components used throughout the US military.