Adsorption of Water and Ammonia on Graphene: Evidence for Chemisorption from X-ray Absorption Spectra

Böttcher, Stefan; Vita, Hendrik; Weser, Martin; Bisti, F.; Dedkov, Yuriy; Horn, Karsten

doi:10.1021/acs.jpclett.7b01085

Cited by 23 publications

(32 citation statements)

References 42 publications

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“…The large residual for the interior region, particularly around 402 to 408 eV (Figure S9b, Supporting Information), is a result of an incomplete basis set of input spectra. The likely missing component is a surface species in which the bonding to nitrogen is similar to that of adsorbed ammonia, which has substantial X‐ray absorption in that region as seen in other studies, because NH 3 has been proposed as a mediator in the dehydrogenation reaction 8c,e,f. Noninclusion of the spectrum of this ammonia‐like species is not expected to affect significantly the mapping of the solid phases or the overall phase structure.…”

mentioning

confidence: 82%

The Inside‐Outs of Metal Hydride Dehydrogenation: Imaging the Phase Evolution of the Li‐N‐H Hydrogen Storage System

White

Baker

Marcus

et al. 2020

Adv Materials Inter

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Hydrogen fuel cell technology has been proposed as a means of reducing the dependence on fossil fuels and enabling energy resiliency in transportation and other applications. [1] Key to the widespread deployment of hydrogen, particularly for mobile applications, is high-density reversible storage. Complex metal hydrides possess both large gravimetric and volumetric hydrogen densities, up to 15 wt% and over 100 kg m −3 . [1a,2] The two major challenges preventing the widespread use of complex metal hydrides are the sluggish kinetics at low temperatures Complex metal hydrides provide high-density hydrogen storage, which is essential for vehicular applications. However, the practical application of these materials is limited by thermodynamic and kinetic barriers present during the dehydrogenation and rehydrogenation processes as new phases form inside parent phases. An improved understanding of the mixed-phase mesostructures and their interfaces will assist in improving cyclability. In this work, the phase evolution during hydrogenation of lithium nitride and dehydrogenation of lithium amide with lithium hydride is probed with scanning transmission X-ray microscopy at the nitrogen K edge. With this technique, core-shell structures are observed in particles of both partially hydrogenated Li 3 N and partially dehydrogenated LiNH 2 + 2LiH. To generate these structures, the rate-limiting step must shift from internal hydrogen diffusion during hydrogenation to the formation of hydrogen gas at the surface during desorption.

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mentioning

confidence: 82%

The Inside‐Outs of Metal Hydride Dehydrogenation: Imaging the Phase Evolution of the Li‐N‐H Hydrogen Storage System

White

Baker

Marcus

et al. 2020

Adv Materials Inter

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“…Interestingly Böttcher et al 9 obtain a similar adsorption energy of 146 meV for NH 3 on graphene/Ni(111) from vdW corrected DFT, however, the molecule is adsorbed in the upwards configuration on graphene/Ni(111). On the other hand, recent X-ray absorption spectroscopy measurements provided evidence for a chemical contribution to the adsorption bond in the case of NH 3 adsorbed on graphene/Ni(111) 65 . Hence it is possible that due to the present metal substrate the adsorption geometry of the ammonia molecule on graphene/Ni(111) changes compared to ammonia adsorbed on graphite.…”

Section: A Dft Resultsmentioning

confidence: 99%

Ultrafast molecular transport on carbon surfaces: The diffusion of ammonia on graphite

Tamtögl

Sacchi

Calvo-Almazán

et al. 2018

Carbon

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We present a combined experimental and theoretical study of the self-diffusion of ammonia on exfoliated graphite. Using neutron time-of-flight spectroscopy we are able to resolve the ultrafast diffusion process of adsorbed ammonia, NH3, on graphite. Together with van der Waals corrected density functional theory calculations we show that the diffusion of NH3 follows a hopping motion on a weakly corrugated potential energy surface with an activation energy of about 4 meV which is particularly low for this type of diffusive motion. The hopping motion includes further a significant number of long jumps and the diffusion constant of ammonia adsorbed on graphite is determined with D = 3.9 · 10 −8 m 2 /s at 94 K.

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“…When the carrier density is fit to the two decay terms from the Langmuir model, the time constants listed earlier provide an optimized reduced chi-squared. Previously reported work indicates that adsorption of oxygen and water on graphene takes place on a similar order of magnitude, [44][45][46][47][48] with oxygen adsorption taking place at slightly slower times at room temperature, assuming that the adsorption follows an Arrhenius behavior. A more detailed analysis of the time-dependency of water adsorption revealed a τ H 2 O .…”

Section: Gateless and Reversible Tuning Of The Carrier Densitymentioning

confidence: 91%

“…A different study on EG measured a time constant on the same order of magnitude when the device was exposed to room temperature air. 49 We can make an estimation based on the measured water desorption energy of 360 meV, 48 and by use of…”

Section: Gateless and Reversible Tuning Of The Carrier Densitymentioning

confidence: 99%

Gateless and reversible Carrier density tunability in epitaxial graphene devices functionalized with chromium tricarbonyl

Rigosi

Kruskopf

Hill

et al. 2019

Carbon

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Monolayer epitaxial graphene (EG) has been shown to have clearly superior properties for the development of quantized Hall resistance (QHR) standards. One major difficulty with QHR devices based on EG is that their electrical properties drift slowly over time if the device is stored in air due to adsorption of atmospheric molecular dopants. The crucial parameter for device stability is the charge carrier density, which helps determine the magnetic flux density required for precise QHR measurements. This work presents one solution to this problem of instability in air by functionalizing the surface of EG devices with chromium tricarbonyl-Cr(CO) 3. Observations of carrier density stability in air over the course of one year are reported, as well as the ability to tune the carrier density by annealing the devices. For low temperature annealing, the presence of Cr(CO) 3 stabilizes the electrical properties and allows for the reversible tuning of the carrier density in millimeter-scale graphene devices close to the Dirac point. Precision measurements in the quantum Hall regime show no detrimental effect on the carrier mobility.

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Adsorption of Water and Ammonia on Graphene: Evidence for Chemisorption from X-ray Absorption Spectra

Cited by 23 publications

References 42 publications

The Inside‐Outs of Metal Hydride Dehydrogenation: Imaging the Phase Evolution of the Li‐N‐H Hydrogen Storage System

The Inside‐Outs of Metal Hydride Dehydrogenation: Imaging the Phase Evolution of the Li‐N‐H Hydrogen Storage System

Ultrafast molecular transport on carbon surfaces: The diffusion of ammonia on graphite

Gateless and reversible Carrier density tunability in epitaxial graphene devices functionalized with chromium tricarbonyl

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