The influence of formic acid on water cluster aggregation has been investigated experimentally by mass spectrometry and tunable UV laser ionization applied to Na‐doped clusters formed in the ...supersonic expansion of water vapors seeded with formic acid (FA) as well as theoretically using high level quantum chemistry methods. The mass spectra of Na−FA(H2O)n clusters show an enlarging of mass distribution toward heavier clusters with respect to the Na−(H2O)n clusters, suggesting similar mass distribution in neutral clusters and an influence of formic acid in water aggregation. Density functional theory and coupled‐cluster type (DLPNO‐CCSD(T)) calculations have been used to calculate structures and energetics of neutral and ionized Na−FA(H2O)n as well as neutral FA(H2O)n. Na‐doped clusters are characterized by very stable geometries. The theoretical adiabatic ionization potential values match pretty well the measured appearance energies and the calculated first six electronic excited states show Rydberg‐type characters, indicating possible autoionization contributions in the mass spectra. Finally, theoretical calculations on neutral FA(H2O)n clusters show the possibility of similarly stable structures in small clusters containing up to n=4–5 water molecules, where FA interacts significantly with waters. This suggests that FA can compete with water molecules in the starting stage of the aggregation process, by forming stable nucleation seed.
Cluster formation: Water aggregation in presence of formic acid at low concentration was investigated by mass spectrometry/photoionization spectroscopy. Experimental data show the formation of larger clusters in the presence of acid molecules. DFT and coupled‐cluster type (DLPNO‐CCSD(T)) calculations support experimental results and suggest that water molecules aggregate preferentially with acid molecule but mainly in the first stage of cluster formation.
The processes involved in the photoionization of sodium‐doped clusters are complex, not fully understood for many systems and still strongly debated, especially because of the discrepancy between ...experimental results and predicted cluster structures. We have performed a study on sodium doped formic acid clusters based on UV photoionization spectroscopy and DFT/TDDFT calculations. Apart from the monomer, all the predicted structures show vertical ionization potential values higher than those obtained by the photoionization measurements. We have calculated the absorption spectra and found many Rydberg‐like states near the adiabatic ionization potentials and, crucially, in the UV range where the clusters appearance energies fall. This finding supports the hypothesis of adiabatic contributions in the measured ionization potentials for these clusters.
Low ionization threshold: Why can a cluster be photoionized although its ionization potential is much higher than the ionizing energy?
The incorporation of aluminum anodes in metal-air galvanic cells is very interesting due to its intrinsic physico-chemical properties that include a high theoretical specific capacity (2.98 Ah g
−1
) ...compared to lithium (3.86 Ah g
−1
), low density, negative standard potential versus the standard hydrogen electrode (SHE), high abundance in the earth's crust, recyclability, and environmental friendliness. In this report, various hydrogels based on xanthan are described that were prepared at different pH values in order to produce solid electrolytes characterized by high ionic conductivity. These electrolytes have been characterized in aluminum-air galvanic cells using Pt/C based air cathodes. The performance of the cells was characterized by discharge tests performed at constant currents across the range from 3 to 6 mA/cm
2
. The ability of recharging the cells was evaluated by determining the electrolyte electrochemical window using cyclic voltammetry (CV) measurements. The ionic conductivity of the hydrogels was determined by electrochemical impedance spectroscopy (EIS). The results evidenced the superior performance of acidic hydrogels in terms of cell capacity and anodic efficiency, due to the capability of xanthan as self-corrosion inhibitor, but the rechargeability was hindered because of the current consuming hydrogen reduction. A larger electrochemical window was observed for neutral hydrogels, but with low cell voltage, and by alkaline electrolytes, but at the expense of the anodic efficiency.
Different commercial carbonaceous materials, two made of activated carbons and one of multiwalled nanotubes, were used to prepare cathodes for primary aluminum-air cells and compared with the more ...expensive platinum-dispersed carbon, usually used as cathode for many types of metal-air cells. The aluminum-air cells used in the electrochemical tests were assembled with alkaline gel polymer electrolytes without any separator. Cells with cathodes made of a cheap activated carbon showed better electrochemical performances than those obtained with platinum-based cathodes. Notably, their discharge capacities were improved and the discharge voltages were always higher than 0.2 V. These improved performances were mainly attributed to the better electrocatalytic activity of the activated carbon as it results from polarization measurements, probably due to the presence of defects, as evidenced from Raman spectra. Three-electrode discharge tests were used to measure the electrode potentials and their impact to the overall cell electrochemical performances. During the discharge, in all cases, an increase of the anodic potential towards more positive values was observed, while the cathodic potential remained almost constant. Thus, the final failure of the cells was mainly due to the degradation of the anodic interface. This indicates the possibility to further increase the cell capacity by adopting suitable mitigation strategies of anodic parasitic reaction or different electrolyte design, with the final aim to realize efficient, cheap, and eco-friendly aluminum-air cells.
Equilibrium geometries and thermodynamic potentials of the neutral and ionised species of the
$ \hbox {Na}\cdots (\hbox {H}_{2}\hbox {O})_{{n}} $
Na
⋯
(
H
2
O
)
n
(
$ {n}=1,..,8 $
n
=
1
,
.
.
,
8
) ...mixed clusters were computed at MN15/def2-TZVPD level of density functional theory (DFT). The vertical and adiabatic ionisation energies and enthalpies were computed and their cluster size dependence was discussed. Laser-induced ionisation involves electronic excitation through Rydberg-type excited states, which have been characterised using the TDDFT method, including the ωB2PLYP double-hybrid exchange-correlation functional. Ab initio molecular dynamics calculations were performed on a time scale of 20 picoseconds. Fluctuations of the charge and the sodium-oxygen atomic distances predict that, the
$ 3\hbox {s}^{1} $
3
s
1
electron of the sodium atom are transferred from the delocalised Rydberg orbitals to the Rydberg orbitals around the water molecules and the sodium atom becomes positively charged with around 0.6e after the first
$ 10\,\hbox {ps} $
10
ps
. On the other hand, some of the water molecules can move away up to 5 Å from the sodium with a significant negative charge on them. It has been shown that non-radiative relaxation cannot be excluded, they can mostly occur for cases
$ n \geqslant 4 $
n
⩾
4
. The results confirm that the adiabatic photo-ionisation can occur on the basis of cluster disintegration.
The feasibility to recharge aluminum‐air cells realized with a dual water‐based electrolyte without separator is demonstrated. The dual electrolyte, made of polyvinyl alcohol and Xanthan gum, has a ...different water content, lower at the anodic interface, where parasitic reactions involving hydrogen production play a crucial role in hindering metal re‐deposition, and higher at the cathode side, where water, depending on the pH, allows an efficient reduction of oxygen during discharge or the oxygen evolution during cell charging. The galvanostatic cycles show in the first discharge and charge cycles, the characteristic plateau trends of secondary batteries. By electrochemical impedance spectroscopy analysis effected after each discharge/charge phase and by measuring anode and cathode potentials during cycling, it is demonstrated that, during the first cycles, the re‐deposition of aluminum is possible by adopting adequate water management in the electrolyte, while the cell malfunctioning in the subsequent cycles is mainly due to the damage of the cathode.
A dual solid electrolyte, prepared frombiodegradable materials and aqueous solutions, is used in aluminum‐air batteries to verify the possibility of recharging, by maintaining minimum water content on the anode and increasing it on the cathode side. The three‐electrode cycling demonstrates that the batteries can be recharged through suitable water management inside the electrolytes.
The influence of carboxylic acids on water nucleation in the gas phase has been explored in the supersonic expansion of water vapour mixed with acetic acid (AcA) at various concentrations. The ...sodium‐doping method has been used to detect clusters produced in supersonic expansions by using UV photoionisation. The mass spectra obtained at lower acid concentrations show well‐detected Na+AcA(H2O)n and Na+AcA2(H2O)n clusters up to 200 Da and, in the best cooling expansions, emerging Na+AcAm(H2O)n signals at higher masses and unresolved signals that extend beyond m/e values >1000 Da. These signals, which increase with increasing acid content in water vapour, are an indication that the cluster growth taking place arises from mixed water–acid clusters. Theoretical calculations show that small acid–water clusters are stable and their formation is even thermodynamically favoured with respect to pure water clusters, especially at lower temperatures. These findings suggest that acetic acid may play a significant role as a pre‐nucleation embryo in the formation of aerosols in wet environments.
How does your cluster grow? The aggregation of small carboxylic acids and water in the gas phase has been probed in molecular beam experiments on acetic acid. Even at low concentration, the acid favors the formation of large aggregates (see figure). The energetic stability of small acid–water clusters and thermodynamically favored reactions are responsible for this remarkable feature.
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►Photoionisation efficiency spectra of toluene clusters. ►DFT calculations on stacked and non-stacked clusters structures. ►Hints on the toluene clusters growth.
Here we report an ...experimental and computational study of toluene clusters that were formed in a He supersonic jet. A tunable vacuum ultraviolet radiation source was used to measure the ionisation potentials of dimers, trimers and tetramers from the onset of their photoionisation efficiency curves. DFT calculations were performed for different structures of stacked and non-stacked dimers and trimers as well as for a fully-stacked tetramer. Through comparison of the measured and calculated ionisation potentials, we show that under our experimental conditions, toluene nucleation starts from stacked dimers and proceeds through non-stacked trimers and tetramers.
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