Formation Of Solvated Electrons Research Articles

Solvation–Reduction Coupling in Ca2+ Electroactivity in Glyme‐Based Electrolytes: A First Principles Study

AbstractThe electrochemical activity of solvated Ca2+ in glyme‐based electrolytes is investigated using grand canonical density functional theory approach and Fukui functions. The obtained results reveal that the length of glyme molecules has little effect on the reduction potentials, but has significant impacts on the effective electron transfer process. In short chain glymes, the transferred electron is located on a Ca2+ center and the organic part of the solvation sphere, leading to a direct Ca2+ reduction and a partial degradation of the glyme molecules. As the glyme's length increases, the reduction process turns into the formation of solvated electrons rather than Ca2+ reduction, unless a partial desolvation occurs. Consequently, an effective Ca2+ reduction in long chain glyme‐based electrolytes is controlled by a (partial) desolvation of the solvation sphere. These results can be used as guiding information to design new electrolytes having the Ca2+ reduction potential in an accessible voltage range together with an effective Ca2+ reduction process. The methodology developed in this study can be universally applied to investigate the thermodynamic and kinetic properties of other battery systems using metal anodes, which might lead to a paradigm shift in the design of prospective electrolytes for future battery technologies.

Distortion Correction of Low-Energy Photoelectron Spectra of Liquids Using Spectroscopic Data for Solvated Electrons.

Time-resolved photoelectron spectroscopy (TRPES) enables real-time observation of ultrafast electronic dynamics in solutions. When extreme ultraviolet (EUV) probe pulses are employed, they can ionize solutes from all electronic states involved in the dynamics. However, EUV pulses also produce a strong ionization signal from a solvent that is typically 6 orders of magnitude greater than the pump-probe photoelectron signal of solutes. Alternatively, UV probe pulses enable highly sensitive and selective observation of photoexcited solutes because typical solvents such as water are transparent to UV radiation. An obstacle in such UV-TRPES measurements is spectral distortion caused by electron scattering and a yet to be identified mechanism in liquids. We have previously proposed the spectral retrieval (SR) method as an a posteriori approach to removing the distortion and overcoming this difficulty in UV-TRPES; however, its accuracy has not yet been verified by comparison with EUV-TRPES results. In the present study, we perform EUV-TRPES for charge transfer reactions in water, methanol, and ethanol, and verify SR analysis of UV-TRPES. We also estimate a previously undetermined energy-dependent intensity factor and expand the basis sets for SR analysis. The refined SR method is employed for reanalyzing the UV-TRPES data for the formation and relaxation dynamics of solvated electrons in various systems. The electron binding energy distributions for solvated electrons in liquid water, methanol, and ethanol are confirmed to be Gaussian centered at 3.78, 3.39, and 3.25 eV, respectively, in agreement with Nishitani et al. [ Sci. Adv. 2019, 5(8), eaaw6896]. An effective energy gap between the conduction band and the vacuum level at the gas-liquid interface is estimated to be 0.2 eV for liquid water and 0.1 eV for methanol and ethanol.

Shallow and deep trap states of solvated electrons in methanol and their formation, electronic excitation, and relaxation dynamics.

We present condensed-phase first-principles molecular dynamics simulations to elucidate the presence of different electron trapping sites in liquid methanol and their roles in the formation, electronic transitions, and relaxation of solvated electrons (emet−) in methanol. Excess electrons injected into liquid methanol are most likely trapped by methyl groups, but rapidly diffuse to more stable trapping sites with dangling OH bonds. After localization at the sites with one free OH bond (1OH trapping sites), reorientation of other methanol molecules increases the OH coordination number and the trap depth, and ultimately four OH bonds become coordinated with the excess electrons under thermal conditions. The simulation identified four distinct trapping states with different OH coordination numbers. The simulation results also revealed that electronic transitions of emet− are primarily due to charge transfer between electron trapping sites (cavities) formed by OH and methyl groups, and that these transitions differ from hydrogenic electronic transitions involving aqueous solvated electrons (eaq−). Such charge transfer also explains the alkyl-chain-length dependence of the photoabsorption peak wavelength and the excited-state lifetime of solvated electrons in primary alcohols.

Below Band Gap Formation of Solvated Electrons in Neutral Water Clusters?

Below band gap formation of solvated electrons in neutral water clusters using pump–probe photoelectron imaging is compared with recent data for liquid water and with above band gap excitation studies in liquid and clusters. Similar relaxation times on the order of 200 fs and 1–2 ps are retrieved for below and above band gap excitation, in both clusters and liquid. The independence of the relaxation times from the generation process indicates that these times are dominated by the solvent response, which is significantly slower than the various solvated electron formation processes. The analysis of the temporal evolution of the vertical electron binding energy and the electron binding energy at half-maximum suggests a dependence of the solvation time on the binding energy.

Solvated electron formation from the conduction band of liquid methanol: Transformation from a shallow to deep trap state

We report solvated electron (esolv -) formation dynamics from the conduction band of liquid methanol studied using femtosecond time-resolved photoelectron spectroscopy. Liquid methanol is excited with vacuum UV (9.3 eV) pump pulses, and the subsequent electron dynamics are probed with UV pulses. The photoelectron signal exhibits a short-lived component (τ = 85 fs) without spectral evolution followed by a long-lived component with continuous spectral evolution over tens of picoseconds. We ascribe the former to a superexcited state, most likely the Wannier exciton, and the latter to the ground electronic state of esolv -. In order to extract accurate energetics from the observed photoelectron spectra, we employ a spectral retrieval method to account for spectral broadening and shifting due to inelastic scattering of photoelectrons in the liquid. The electron binding energy (eBE) of the initial trap state of an electron is determined to be about 1.5 eV, and its biexponential increase up to 3.4 eV is observed with time constants of 2 and 31 ps, which are greater than 0.27 and 13 ps observed for esolv - created by the charge-transfer-to-solvent reaction from CH3O- to liquid methanol. The solvation dynamics of esolv - created by the electron trapping exhibit a pseudoisosbestic point at a pump-probe delay time of around 15 ps, and the peak energy of the eBE distribution rapidly changes around that time. These results indicate that there exist two trap states, both of which exhibit increasing eBE with time; however, the eBE of the shallow trap state increases only up to 2.1 eV, and transformation to a deep trap state at 25 ps occurs to reach an eBE of 3.4 eV.

Solvent reorganization triggers photo-induced solvated electron generation in phenol

The analysis of the absorption spectrum and density of states of a cluster of phenol solvated with 15 water molecules indicates that the reorganization of the water molecules, facilitating the formation of solvated electrons, is a plausible mechanism in the photodissociation of phenol. Using quantitative wavefunction analysis, we demonstrate that while charge-transfer states involving electron transfer from phenol to water are mainly dark, a considerable number of them exists below the maximum of the ππ* absorption band and could be populated by internal conversion. These low-lying charge-transfer states do not show extended O-H distances, but are found for large electron-hole separations at which several water molecules can solvate and stabilize the transferred electron. Thus, charge-transfer states in solvated phenol can be stabilized by two factors: (i) elongation of the O-H bond, as was extensively discussed in the past, and (ii) reorganization of solvent molecules, as it is shown here.

Catalyst-Free, Electrolytic Synthesis of Ammonia from Nitrogen and Water By Plasma-Produced Solvated Electrons

Ammonia which is a precursor to fertilizers and food and is one of the most important chemicals in the world is currently synthesized on a large scale by the Haber-Bosch (H-B) process. Recent research has been aimed at developing alternative approaches to synthesizing ammonia to address several issues associated with the H-B process: 1) the very high pressures and high temperatures which lead to enormous capitals costs, 2) the need for hydrogen gas which comes from steam-methane reforming and contributes to high energy costs and environmental impact through greenhouse gas emissions, and 3) the incompatibility with renewable sources of energy that could lower energy costs and environmental impact while also offering more localized, point-of-use sources of ammonia. Here, we report a hybrid electrochemical system to produce ammonia where one of the metal electrodes is replaced by a plasma (gas discharge). Similar to more typical electrochemical systems, ammonia synthesis is carried out at ambient conditions and only requires electricity. However, the interaction of a plasma and water leads to the formation of solvated electrons, one of the strongest reducing agents known with a reduction potential of ~-2.8 V. Production rates and selectivity (i.e. charge-transfer efficiency) were determined as a function of various process parameters including current, time, and electrolyte composition. We will also discuss a potential reaction mechanism based on the observed results.

Metal ion reductions by femtosecond laser pulses with micro-Joule energy and their efficiencies

Abstract Chemical reactions of metal ions in solution were studied using 800 nm, 90 femtosecond laser pulses with a laser intensity range beginning at sub-micro-Joules/pulse, where the intensities were at or just below supercontinuum generation. Products were observed as surface resonance absorptions assignable to Ag, Au nanoparticles (NPs) and light scattering, indicating the formation of Pd NPs. The consumption efficiencies of metal ions from the Au and Pd ions were estimated to be 10−3 per incident photon. The major absorbing species of the laser energy was water, which led to the formation of solvated electrons that acted as a reducing agent of metal ions, while direct multi-photon dissociation to neutral atoms was unlikely. Metal ion Fe3+and Yb3+ systems are also discussed, where Fe3+ to Fe2+ was ascribed to two-photon absorption and Yb3+ to Yb2+ to a reduction followed by solvent ionization.

Discrete models for describing photophysical and thermodynamic properties of polar liquids

A number of properties of liquids with polar molecules are considered using water and ammonia as examples in the discrete approach, i.e., placing the centers of molecules on nodes of a particular lattice while assuming different orientations of the molecules. Different experimental properties are explained by different assumptions concerning the average values of pair orientations of adjacent molecules. Rather than using a uniform thermodynamic distribution over orientations to study fast processes related to the formation and migration of solvated electrons, a quasi-chemical approximation of the lattice gas model is used to calculate the thermodynamic properties of a liquid.

Ionic Valence Change of Metal Ions in Solution by Femtosecond Laser Excitation Accompanied by White-Light Laser

Three lanthanide ions (Ln^(3+)), Ln = Eu, Sm, and Yb, and two transition metals, Fe^(3+) and Ag^+, were found to be reduced to the corresponding Ln^(2+), Fe^(2+), and Agn in methanol or aqueous solution upon irradiation with intense femtosecond laser pulses. The major excitation wavelength was 800 nm and single-photon-non-resonant with the electronic transitions of metal ion solutions. Laser pulses with wavelengths of 970, 1190, and 1930 nm were used for particular cases. Whenever the white-light laser was generated, the reductions were observed. The reduction mechanisms would be explained in terms of self-focusing, solvated electron formation followed by trapping the electron. The electron ejection under focused beam conditions in solution has been known to be accompanied by white-light laser. In the exceptional case of Fe^(3+) at 800 nm, two-photon excitation of the charge transfer state followed by the reduction would be operative. Fe^(2+) was detected even with an intensity lower than the threshold of the white-light laser generation.

Photoemission from diamond films and substrates into water: dynamics of solvated electrons and implications for diamond photoelectrochemistry.

Illumination of diamond with above-bandgap light results in emission of electrons into water and formation of solvated electrons. Here we characterize the materials factors that affect that dynamics of the solvated electrons produced by illumination of niobium substrates and of diamond thin films grown on niobium substrates using transient absorption spectroscopy, and we relate the solvated electron dynamics to the ability to reduce N2 to NH3. For diamond films grown on niobium substrates for different lengths of time, the initial yield of electrons is similar for the different samples, but the lifetime of the solvated electrons increases approximately 10-fold as the film grows. The time-averaged solvated electron concentration and the yield of NH3 produced from N2 both show maxima for films grown for 1-2 hours, with thicknesses of 100-200 nm. Measurements at different values of pH on boron-doped diamond films show that the instantaneous electron emission is nearly independent of pH, but the solvated electron lifetime becomes longer as the pH is increased from pH = 2 to pH = 5. Finally, we also illustrate an important caveat arising from the fact that charge neutrality requires that light-induced emission of electrons from diamond must be accompanied by corresponding oxidation reactions. In situations where the valence band holes cannot readily induce solution-phase oxidation reactions, the diamond itself can be etched by reacting with water to produce CO. Implications for other reactions such as photocatalytic CO2 reduction are discussed, along with strategies for mitigating the potential photo-etching phenomena.

Sodium doped hydrogen bonded clusters: Solvated electrons and size selection

Neutral, sodium doped clusters feature special properties related to solvated electron formation which allow for a wide range of applications. In case of water, methanol and ethanol – but not for ammonia – the evolution of the ionization energy stops at small cluster sizes, reaching values similar to binding energies of solvated electrons in the liquid phase. Because of the appreciable lowering of the ionization energy, their photoionization can be performed free of fragmentation by standard lasers. This provides a very effective method for detection and, in combination with infrared excitation, for taking OH-stretch spectra of size selected, neutral clusters.

Network topology for the formation of solvated electrons in binary CaO–Al 2 O 3 composition glasses

Glass formation in the CaO-Al2O3 system represents an important phenomenon because it does not contain typical network-forming cations. We have produced structural models of CaO-Al2O3 glasses using combined density functional theory-reverse Monte Carlo simulations and obtained structures that reproduce experiments (X-ray and neutron diffraction, extended X-ray absorption fine structure) and result in cohesive energies close to the crystalline ground states. The O-Ca and O-Al coordination numbers are similar in the eutectic 64 mol % CaO (64CaO) glass [comparable to 12CaO·7Al2O3 (C12A7)], and the glass structure comprises a topologically disordered cage network with large-sized rings. This topologically disordered network is the signature of the high glass-forming ability of 64CaO glass and high viscosity in the melt. Analysis of the electronic structure reveals that the atomic charges for Al are comparable to those for Ca, and the bond strength of Al-O is stronger than that of Ca-O, indicating that oxygen is more weakly bound by cations in CaO-rich glass. The analysis shows that the lowest unoccupied molecular orbitals occurs in cavity sites, suggesting that the C12A7 electride glass [Kim SW, Shimoyama T, Hosono H (2011) Science 333(6038):71-74] synthesized from a strongly reduced high-temperature melt can host solvated electrons and bipolarons. Calculations of 64CaO glass structures with few subtracted oxygen atoms (additional electrons) confirm this observation. The comparable atomic charges and coordination of the cations promote more efficient elemental mixing, and this is the origin of the extended cage structure and hosted solvated (trapped) electrons in the C12A7 glass.

Electron transfer in N-butylpyridinium tetrafluoroborate ionic liquid by pulse radiolysis

The radiolysis behavior of neat pyridinium ionic liquids (ILs) and their aqueous solutions was investigated using nanosecond pulse radiolysis techniques. Radiolysis of the ionic liquids, such as N-butylpyridinium tetrafluoroborate (BuPyBF4), resulted in the formation of solvated electrons and organic radicals. Solvated electrons reacted with the pyridinium moiety to produce a pyridinyl radical, which can transfer electrons to various acceptors. The electron-transfer rate constants of the solvent-derived butylpyridinyl radicals in BuPyBF4 and in several compounds (for example, duroquinone, 4,4′-pyridine, benzophenone, and 1,1′-dimethyl-4,4′-bypyridinium dichloride) (k of the order 108 L/(mol s) were lower than those measured in water and in i-PrOH but were significantly higher than the diffusion-controlled rate constants estimated based on viscosity. The electron-transfer rate constants in neat BuPyBF4 were one order of magnitude faster than the diffusion-controlled values. This finding suggests that Bu-PyBF4 acts not only as solvent but also as active solute, such as in solvent-mediated reactions. These reactions result in electrons reaching their final destinations via intervening pyridinium groups without requiring the diffusion of a specific radical.

アルミン酸カルシウムガラスにおける溶媒和電子の形成を促すかご状構造

アルミン酸カルシウムガラスにおける溶媒和電子の形成を促すかご状構造

ChemInform Abstract: Solvated Electrons in High‐Temperature Melts and Glasses of the Room‐Temperature Stable Electride [Ca24Al28O64] 4+·4e‐.

AbstractThe formation of persistent solvated electrons in both a high‐temperature melt of the title electride and its glass is demonstrated by electrical conductivity measurements, XRD, TEM, and Raman spectroscopy.

Tripodal Osmium Polypyridyl Complexes for Self-Assembly on Platinum Nanoparticles

The combination of platinum nanoparticles with a tripodal osmium complex that anchors to the metal surface leads, under visible light irradiation, to the formation of solvated electrons. The formation kinetics is limited by the detachment of the electron from the platinum surface into the solution, the particle showing a type of capacitor behavior.

Decomposition of halophenols in room-temperature ionic liquids by ionizing radiation

In this article, we report the reaction of halophenols with solvated electrons in room-temperature ionic liquids (RTILs) initiated by γ-ray and pulsed electron radiolyses. The decomposition G-values of ortho-chlorophenol (CP) in N-methyl- N-propylpyrrolidinium–bis(trifluoromethanesulfonyl)imide (TFSI), N-butyl- N-methylpyrrolidinium–TFSI and N-methyl- N-propylpiperidinium–TFSI were estimated to be 1.4, 1.6, and 1.7 molecules 10 −2 eV −1 under γ-ray irradiation; these values were almost the same as the yield of solvated electron formation. The second-order rate constant for the reaction of CP with solvated electrons in diethylmethyl(2-methoxyethyl)ammonium (DEMMA)–tetrafluoroborate (BF 4) was one order of magnitude lower than that in DEMMA–TFSI although the G-values of CP decomposition and phenol formation in DEMMA-BF 4 were higher. The decomposition yield of ortho-iodophenol in DEMMA–TFSI was slightly higher than that of the other halophenol ( ortho-fluorophenol, CP, and ortho-bromophenol), and the formation yield of phenol for the decomposition of only ortho-fluorophenol was lower.

Laser ablation of silver and gold in liquid ammonia

Laser ablation of a silver (Ag) and/or gold (Au) target was performed in liquid ammonia (l-NH3) at 233 K using nanosecond laser pulses of 1064, 532 and 355 nm wavelengths. An “in situ” monitoring of the ablation process by UV/vis/NIR spectroscopy has shown the evolution of the surface plasmon extinction band of silver or gold nanoparticles and thus confirmed their formation. While sols of Au nanoparticles in l-NH3 are quite stable in air, those of Ag nanoparticles undergo oxidation to Ag(I) complexes with NH3 ligands. On the other hand, formation of solvated electrons, namely of the (e−)NH3 solvates, has not been unequivocally confirmed under the conditions of our laser ablation/nanoparticle fragmentation experiment, since only very weak vis/NIR spectral features of these solvates were observed with a low reproducibility. Reference experiments have shown that the well-known chemical production of these solvates is hindered by the presence of Ag and Au plates. Ag and Au targets can thus possibly act as electron scavengers in our ablation experiments.

Reduction of Eu 3+ to Eu 2+ by an intense femtosecond laser pulse in solution

Europium 3+ ions in methanol were found to be reduced to the corresponding 2+ ions upon irradiation with intense femtosecond laser pulses. The excitation wavelength of 800 nm was nonresonant with their electronic transitions of Eu 3+. It is notable that femtosecond white-light laser was generated when the reactions occurred. The mechanisms can be explained in terms of solvated electron formation followed by the reduction. The electron ejection in a focused beam in solution has been known to be accompanied by white-light laser.