Heterolytic Scission of Hydrogen Within a Crystalline Frustrated Lewis Pair

We report the heterolysis of molecular hydrogen under ambient conditions by the crystalline frustrated Lewis pair (FLP) 1-{2-[bis (pentafluorophenyOboryl] phenyl -2, 2,6,6-tetrame-thylpiperidine (KCAT). The gas-solid reaction provides an approach to prepare the solvent-free, polycrystalline ion pair KCATH2 through a single crystal to single crystal transformation. The crystal lattice of KCATH2 increases in size relative to the parent KCAT by approximately 2%. Microscopy was used to follow the transformation of the highly colored red/orange KCAT to the colorless KCATH2 over a period of 2 h at 300 K under a flow of H-2 gas. There is no evidence of crystal decrepitation during hydrogen uptake. Inelastic neutron scattering employed over a temperature range from 4-200 K did not provide evidence for the formation of polarized H-2 in a precursor complex within the crystal at low temperatures and high pressures. However, at 300 K, the INS spectrum of KCAT transformed to the INS spectrum of KCATH2. Calculations suggest that the driving force is more favorable in the solid state compared to the solution or gas phase, but the addition of H-2 into the KCAT crystal is unfavorable. Ab Initio methods were used to calculate the INS spectra of KCAT, KCATH2, and a possible precursor complex of H-2 in the pocket between the B and N of crystalline KCAT. Ex-situ NMR showed that the transformation from KCAT to KCATH2 is quantitative and our results suggest that the hydrogen heterolysis process occurs via H-2 diffusion into the FLP crystal with a rate-limiting movement of H-2 from inactive positions to reactive sites.Peer reviewe

Patterns of Plasma Filaments Propagating on a Dielectric Surface

International audienc

Fundamental Insight into Humid CO2 Uptake in Direct Air Capture Nanocomposites Using Fluorescence and Portable NMR Relaxometry

Direct air capture (DAC) technology is being explored as a pathway for reducing greenhouse gas emissions through the efficient removal of CO2 from the atmosphere. However, there remains a knowledge gap regarding structure-property-performance factors that impact the behavior of these systems in diverse, real-world environments. In aminopolymer-based DAC systems, gas diffusion is tightly coupled with polymer mobility, which is in turn affected by a large matrix of variables, including interactions with the pore wall of the support, nanoconfinement, the presence of co-adsorbates (moisture), and electrostatic crosslinks that develop as a function of CO2 chemisorption. Higher throughput, benchtop techniques for studying and understanding mobility in these systems would lead to more rapid advances in the field. Here, we demonstrate the value of a fluorescence technique for monitoring polymer mobility within nanocomposite capture materials as a function of CO2 and water adsorption in a series of humidified polyethylenimine-Al2O3 composite materials. The approach allows us to correlate changes in mobility with CO2 adsorption kinetics as a function of relative humidity. We further couple this information with NMR relaxometry data attained using a portable single-sided magnetic resonance device, and we employ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to correlate the formation of different relative amounts of carbamates and carbonates with the environmental conditions. These results provide a blueprint for using benchtop techniques to promote fundamental understanding in DAC systems that can in turn enable more efficient operation in real-world conditions

Atomic Layer Deposition of SiC_<i>x</i>N_<i>y</i> Using Si₂Cl₆ and CH₃NH₂ Plasma

We developed a novel process for the atomic layer deposition (ALD) of SiC_<i>x</i>N_<i>y</i> films using a Si₂Cl₆ and a CH₃NH₂ plasma. Under self-limiting growth conditions, this ALD process led to SiC_<i>x</i>N_<i>y</i> films with up to 9 atomic percent carbon with a conformality >95% in 5:1 aspect ratio nanostructures. The surface reactions during ALD, and in particular the carbon incorporation mechanism, were studied using in situ attenuated total reflection Fourier transform infrared spectroscopy. Similar to the Si₂Cl₆ and NH₃ plasma-based process, we show that on the SiC_<i>x</i>N_<i>y</i> growth surface, Si₂Cl₆ reacts primarily with surface −NH₂ species that were created after the CH₃NH₂ plasma cycle. During the subsequent CH₃NH₂ half cycle, the surface chlorine was liberated, creating −NH_<i>x</i> (<i>x</i> = 1 or 2) groups, while carbon was incorporated primarily as −NCN– species. In situ ellipsometry showed that the growth per cycle and the refractive index were ∼1 Å and ∼1.85, respectively. Elemental depth profiling with secondary ion mass spectrometry showed that, as the plasma power was increased from 50 to 100 W, the carbon atomic fraction increased from ∼4 to ∼9%. At higher plasma powers, the CH₃NH₂ plasma half cycle was not self-limiting and led to continuous carbon nitride growth

Additive Destabilization of Porous Magnesium Borohydride Framework with Core-Shell Structure.

Design of interfaces with thermodynamic and kinetic specificity is of great importance for hydrogen storage from both an applied and fundamental perspective. Here, in order to destabilize the metal hydride and protect the dehydrogenated products from oxidizing, a unique core-shell structure of porous Mg(BH4 )2 -based framework with a thin layer (no more than 5&nbsp;nm) of MgCl2 additives on the surface, has been proposed and synthesized via a wet-chemical method. The local structure and electronic state of the present complex system are systematically investigated to understand the correlation between the distribution of additives and dehydrogenation property of Mg(BH4 )2 . A significant improvement is achieved for hydrogen desorption with chlorides: initial hydrogen release from MgCl2 decorated γ-phase Mg(BH4 )2 particles commences at 100&nbsp;°C and reaches a maximum of 9.4 wt% at 385&nbsp;°C. Besides the decreased decomposition temperature, an activation barrier of about 76.4&nbsp;kJ mol-1 lower than that of Mg(BH4 )2 without MgCl2 is obtained. Moreover, MgCl2 decoration can also prevent the whole decomposed system (both Mg- and B- elements) from oxidizing, which is a necessary condition to reversibility