Shuttling protons in ammonia synthesis
An electrochemical route to ammonia could substantially lower the greenhouse gas emissions associated with the current thermal Haber-Bosch process. One ...relatively promising option under study involves reductive formation of lithium nitride, which can be protonated to ammonia. However, the ethanol used to date as a local proton source in these studies may degrade under the reaction conditions. Suryanto
et al.
report the use of a tetraalkyl phosphonium salt in place of ethanol (see the Perspective by Westhead
et al.
). This cation can stably undergo deprotonation–reprotonation cycles and, as an added benefit, it enhances the ionic conductivity of the medium.
Science
, abg2371, this issue p.
1187
; see also abi8329, p.
1149
A phosphonium cation acts as a stable proton shuttle during electrochemical ammonia synthesis.
Ammonia (NH
3
) is a globally important commodity for fertilizer production, but its synthesis by the Haber-Bosch process causes substantial emissions of carbon dioxide. Alternative, zero-carbon emission NH
3
synthesis methods being explored include the promising electrochemical lithium-mediated nitrogen reduction reaction, which has nonetheless required sacrificial sources of protons. In this study, a phosphonium salt is introduced as a proton shuttle to help resolve this limitation. The salt also provides additional ionic conductivity, enabling high NH
3
production rates of 53 ± 1 nanomoles per second per square centimeter at 69 ± 1% faradaic efficiency in 20-hour experiments under 0.5-bar hydrogen and 19.5-bar nitrogen. Continuous operation for more than 3 days is demonstrated.
In this work, we report that the surface hydroxylation of C60 molecules is the most likely mechanism for pristine C60 fullerenes/C60 fullerene aggregate stabilization in water, being independent of ...the method of C60 fullerene aqueous solution preparation.
Stable metal anode cycling for high energy density batteries can be realized through modification of electrolyte composition and optimization of formation protocols, i.e., electrode interphase ...preconditioning conditions. However, the relationship between these and the electrochemical performance is still unclear due to a lack of molecular level understanding of electric double layer (EDL) changes with modification of these two parameters. Herein, we examine the impact of ionic liquid (IL) electrolyte composition (salt concentration and cosolvent) and preconditioning cycling conditions on Li anode performance through EDL changes affecting both the solid–electrolyte interphase (SEI) and deposition morphology. Each electrolyte composition results in a particular interfacial Li-ion solvation environment, which controls the reductive stability, Li deposition potential, and ultimately the composition of properties of the SEI. The latter is dependent on the EDL composition such as the IL cation/Li-anion ratio or the presence of other surface active additives. It is found that in a superconcentrated electrolyte, a high current density (≥10.0 mA cm–2/1.0 mAh cm–2) is beneficial during the metal anode preconditioning step, compared with the case of low Li salt-containing IL. This correlates with a predominance of Li x (anion) y (x > y) at a highly negatively charged interface, which is present when higher current densities are used for preconditioning, as suggested by molecular dynamics simulations. In contrast, for the lower viscosity superconcentrated electrolyte containing 20 wt % of ether cosolvent, a more moderate preconditioning step current density (6.0 mA cm–2/1.0 mAh cm–2) leads to an optimized deposition morphology and improved cycling performance. This is a consequence of the competing processes of ion transport at the interface, which controls the Li+ ion flux and the intrinsic reduction kinetics occurring at the more negative electrode.
Mathematical modeling of spectral-kinetic, thermal, and electrophysical characteristics, which are difficult to determine experimentally, has been carried out based on the available experimental data ...for a promising class of the latest high-temperature composite materials consisting of mullite−corundum fibers. The model based on the concept of a representative element makes it possible to take into account not only the structural regularities of the materials and the thermal and electrical properties of its constituents, but also the features (in particular, anisotropy) of radiation in their volume and a wide range of external conditions. After the model is adjusted to the experimental data (thermophysical or spectral), it is possible to calculate the necessary characteristics of materials as a whole and to study the physical processes in heterogeneous, highly porous structures on different spatial and temporal scales. In this study, the model was adjusted to the published results of a thermophysical experiment, which made it possible to determine over a wide temperature range the key parameters to take into account cooperative effects when the fragments of the material interact with electromagnetic radiation. New, important data on the thermal conductivity of materials and its conductive and radiative components, heat capacity, electrical resistivity, and dielectric permittivity have been obtained. A study on those external conditions that make experimentation substantially difficult has been carried out, and specific recommendations regarding the optimization of the properties of the materials are given. The results of the work clearly demonstrate the effectiveness of mathematical materials science as a tool that significantly expands the capabilities of experimental methods.
We calculated the cross sections of photolysis of OH, LiO, NaO, KO, HCl, LiCl, NaCl, KCl, HF, LiF, NaF, and KF molecules using quantum chemistry methods. The maximal values for photolysis cross ...sections of alkali metal monoxides are on the order of 10
−18
cm
2
. The lifetimes of photolysis for quiet Sun at 1 astronomical unit are estimated as 2.0 × 10
5
, 28, 5, 14, 2.1 × 10
5
, 225, 42, 52, 2 × 10
6
, 35 400, 486, and 30 400 s for OH, LiO, NaO, KO, HCl, LiCl, NaCl, KCl, HF, LiF, NaF, and KF, respectively. We performed a comparison between values of photolysis lifetimes obtained in this work and in previous studies. Based on such a comparison, our estimations of photolysis lifetimes of OH, HCl, and HF have an accuracy of about a factor of 2. We determined typical kinetic energies of main peaks of photolysis-generated metal atoms. Impact-produced LiO, NaO, KO, NaCl, and KCl molecules are destroyed in the lunar and Hermean exospheres almost completely during the first ballistic flight, while other considered molecules are more stable against destruction by photolysis.
A series of La
2−
x
Sr
x
Ni
1−
y
Fe
y
O
4+
δ
complex oxides adopting the K
2
NiF
4
-type structure (sp.gr.
I
4/
mmm
) was prepared
via
the decomposition of citrate-nitrate precursors, followed by ...multiple annealing treatments at 1100 °C in air. Strontium for lanthanum substitution in La
2−
x
Sr
x
Ni
1−
y
Fe
y
O
4+
δ
leads to a progressive increase of iron solubility (
y
) which reaches maximum values at
x
= 1.0-1.2. The crystal structure of single-phase samples was refined by the Reitveld method. The unit cell volume increases with
y
and decreases with
x
in La
2−
x
Sr
x
Ni
1−
y
Fe
y
O
4+
δ
. The solid solutions of La
2−
x
Sr
x
Ni
1−
y
Fe
y
O
4+
δ
were shown by TGA to be over-stoichiometric (
δ
> 0) at
x
= 0.5 and 0.6 and oxygen deficient (
δ
< 0) at
x
= 0.8 within the temperature range of 25-1050 °C in air. The thermal expansion coefficient of La
2−
x
Sr
x
Ni
1−
y
Fe
y
O
4+
δ
increases with
x
and
y
, varying within the range of (12-16) × 10
−6
K
−1
up to 700 °C in air. In the higher temperature range, the value of the TEC increases up to 20 × 10
−6
K
−1
due to a chemical expansion contribution. The total conductivity and Seebeck coefficient were measured in air from RT to 1100 °C. The maximum conductivity value equal to 289 S cm
−1
was obtained for La
1.2
Sr
0.8
Ni
0.9
Fe
0.1
O
4+
δ
at 460 °C in air. The conduction is temperature activated for all samples within the composition range under study. The temperature dependencies of the Seebeck coefficient were explained in the approximation of the small-polaron hopping mechanism. The charge carriers were electron holes localized on nickel forming Ni
3+
cations in low- and high-spin states.
Phase boundaries of tetragonal La
2−
x
Sr
x
Ni
1−
y
Fe
y
O
4+
δ
solid solutions (sp.gr.
I4/mmm
) prepared
via
the decomposition of citrate-nitrate precursors, followed by multiple annealing treatments at 1100 °C in air and quenched to RT.
The aim of this paper was to provide the physico-chemical characterization of a key process leading to amplification of the antitumor effect of antibiotic Doxorubicin (Dox) in vivo and in vitro and ...occurring at the molecular level through complexation with C60 fullerene. A wide range of physico-chemical tools was used such as UV/Vis and NMR spectroscopies, atomic force microscopy, isothermal titration calorimetry and zeta-potential methods. The unusual thermodynamic behavior of the complexation process was reported, featuring unexpected and, to a certain extent, contradictory experimental observations. The explanation of the obtained results was proposed resulting in creation of a general view on aromatic drug binding with C60 fullerene. Based on these results some important practical outcomes for anticancer therapy were formulated.
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