Tough and Recyclable Phase-Separated Supramolecular Gels via a Dehydration-Hydration Cycle.

Hydrogels are compelling materials for emerging applications including soft robotics and autonomous sensing. Mechanical stability over an extensive range of environmental conditions and considerations of sustainability, both environmentally benign processing and end-of-life use, are enduring challenges. To make progress on these challenges, we designed a dehydration-hydration approach to transform soft and weak hydrogels into tough and recyclable supramolecular phase-separated gels (PSGs) using water as the only solvent. The dehydration-hydration approach led to phase separation and the formation of domains consisting of strong polymer-polymer interactions that are critical for forming PSGs. The phase-separated segments acted as robust, physical cross-links to strengthen PSGs, which exhibited enhanced toughness and stretchability in its fully swollen state. PSGs are not prone to overswelling or severe shrinkage in wet conditions and show environmental tolerance in harsh conditions, e.g., solutions with pH between 1 and 14. Finally, we demonstrate the use of PSGs as strain sensors in air and aqueous environments.

Air Stabilization of Li7P3S11 Solid-State Electrolytes through Laser-Based Processing.

All-solid-state batteries (ASSBs) that employ solid-state electrolytes (SSEs) have the potential to replace more conventional batteries that employ liquid electrolytes due to their inherent safety, compatibility with lithium metal and reputable ionic conductivity. Li7P3S11 is a promising SSE with reported ionic conductivities in the order of 10 mS/cm. However, its susceptibility to degradation through oxidation and hydrolysis limits its commercial viability. In this work, we demonstrate a laser-based processing method for SSEs to improve humidity stability. It was determined that laser power and scanning speed greatly affect surface morphology, as well as the resulting chemical composition of Li7P3S11 samples. Electrochemical impedance spectroscopy revealed that laser treatment can produce SSEs with higher ionic conductivities than pristine counterparts after air exposure. Further examination of chemical composition revealed an optimal laser processing condition that reduces the rate of P2S74- degradation. This work demonstrates the ability of laser-based processing to be used to improve the stability of SSEs.

Untying the Cesium "Not": Cesium-Iodoplumbate Complexation in Perovskite Solution-Processing Inks Has Implications for Crystallization.

We illustrate the critical importance of the energetics of cation-solvent versus cation-iodoplumbate interactions in determining the stability of ABX3 perovskite precursors in a dimethylformamide (DMF) solvent medium. We have shown, through a complementary suite of nuclear magnetic resonance (NMR) and computational studies, that Cs+ exhibits significantly different solvent vs iodoplumbate interactions compared to organic A+-site cations such as CH3NH3+ (MA+). Two NMR studies were conducted: 133Cs NMR analysis shows that Cs+ and MA+ compete for coordination with PbI3- in DMF. 207Pb NMR studies of PbI2 with cationic iodides show that perovskite-forming Cs+ (and, somewhat, Rb+) do not comport with the 207Pb chemical shift trend found for Li+, Na+, and K+. Three independent computational approaches (density functional theory (DFT), ab initio Molecular Dynamics (AIMD), and a polarizable force field within Molecular Dynamics) yielded strikingly similar results: Cs+ interacts more strongly with the PbI3- iodoplumbate than does MA+ in a polar solvent environment like DMF. The stronger energy preference for PbI3- coordination of Cs+ vs MA+ in DMF demonstrates that Cs+ is not simply a postcrystallization cation "fit" for the perovskite A+-site. Instead, it may facilitate preorganization of the framework precursor that eventually transforms into the crystalline perovskite structure.

Solvent-induced electrochemistry at an electrically asymmetric carbon Janus particle.

Chemical doping through heteroatom substitution is often used to control the Fermi level of semiconductor materials. Doping also occurs when surface adsorbed molecules modify the Fermi level of low dimensional materials such as carbon nanotubes. A gradient in dopant concentration, and hence the chemical potential, across such a material generates usable electrical current. This opens up the possibility of creating asymmetric catalytic particles capable of generating voltage from a surrounding solvent that imposes such a gradient, enabling electrochemical transformations. In this work, we report that symmetry-broken carbon particles comprised of high surface area single-walled carbon nanotube networks can effectively convert exothermic solvent adsorption into usable electrical potential, turning over electrochemical redox processes in situ with no external power supply. The results from ferrocene oxidation and the selective electro-oxidation of alcohols underscore the potential of solvent powered electrocatalytic particles to extend electrochemical transformation to various environments.

Stable, Temperature-Dependent Gas Mixture Permeation and Separation through Suspended Nanoporous Single-Layer Graphene Membranes.

Graphene membranes with nanometer-scale pores could exhibit an extremely high permeance and selectivity for the separation of gas mixtures. However, to date, no experimental measurements of gas mixture separation through nanoporous single-layer graphene (SLG) membranes have been reported. Herein, we report the first measurements of the temperature-dependent permeance of gas mixtures in an equimolar mixture feed containing H2, He, CH4, CO2, and SF6 from 22 to 208 °C through SLG membranes containing nanopores formed spontaneously during graphene synthesis. Five membranes were fabricated by transfer of CVD graphene from catalytic Cu film onto channels framed in impermeable Ni. Two membranes exhibited gas permeances on the order of 10-6 to 10-5 mol m-2 s-1 Pa-1 as well as gas mixture selectivities higher than the Knudsen effusion selectivities predicted by the gas effusion mechanism. We show that a new steric selectivity mechanism explains the permeance data and selectivities. This mechanism predicts a mean pore diameter of 2.5 nm and an areal pore density of 7.3 × 1013 m-2, which is validated by experimental observations. A third membrane exhibited selectivities lower than the Knudsen effusion selectivities, suggesting a combination of effusion and viscous flow. A fourth membrane exhibited increasing permeance values as functions of temperature from 27 to 200 °C, and a CO2/SF6 selectivity > 20 at 200 °C, suggestive of activated translocation through molecular-sized nanopores. A fifth membrane exhibited no measurable permeance of any gas above the detection limit of our technique, 2 × 10-7 mol m-2 s-1 Pa-1, indicating essentially a molecularly impermeable barrier. Overall, these data demonstrate that SLG membranes can potentially provide a high mixture separation selectivity for gases, with CVD synthesis alone resulting in nanometer-scale pores useful for gas separation. This work also shows that temperature-dependent permeance measurements on SLG can be used to reveal underlying permeation mechanisms.