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The desalination of water in the steady-state and pulsed modes of the supply of the voltage, the value of which corresponds to the conditions of overlimiting current, has been experimentally investigated. The dependences of the current flowing through the electrodialyzer, the water conductivity, and the content of single and double-charged cations at the outlet of the desalination chamber on the value of the applied voltage, the rate of liquid pumping through the electrodialyzer, the initial salt concentration, and the frequency are analyzed. It is shown that the pulsed mode demonstrates, in comparison with the steady-state mode, a decrease in the concentration polarization of the membranes and an increase in the mass transfer in the electrodialyzer in the entire range of used parameters. In addition to the previously proposed mechanism based on the inertia of electroosmosis of the second kind, the increase in mass transfer can be explained by changes in the electromigration mobility of ions, the turbulence of fluid in the intermembrane channel, and the emergence of a bias current and a magnetic field due to voltage pulses in an electric double layer. Considerable attention is also paid to studying the purification of water from cations with different charges. It is found that the removal of zinc cations from the desalination chamber significantly exceeds the removal of sodium cations, which is consistent with previous experimental studies for calcium and sodium cations. However, the obtained results contradict the currently existing three-ion models of competitive ion transport with predominance of the transfer of double-charged cations in the undercurrent mode and single-charged cations in the overcurrent mode. The discrepancy is explained by the dependence of the concentration polarization of the membranes and, accordingly, the transport of salt ions across the membranes on the dissociation of water in the region of space charge, which leads to competitive transport of five ions rather than three ions.

The hemibond is a nonclassical covalent bond formed between a radical (cation) and a closed shell molecule. The hemibond formation ability of water has attracted great interest, concerning its role in ionization of water. While many computational studies on the water hemibond have been performed, clear experimental evidence has been hardly reported because the hydrogen bond formation overwhelms the hemibond formation. In the present study, infrared photodissociation spectroscopy is applied to (H2O-Krn)+ (n = 1-3) radical cation clusters. The observed spectra of (H2O-Krn)+ are well reproduced by the anharmonic vibrational simulations based on the hemibonded isomer structures. The firm evidence of the hemibond formation ability of water is revealed.

The dynamical properties of physically and chemically adsorbed water molecules at pristine hematite-(001) surfaces have been studied by means of nonequilibrium ab initio molecular dynamics (NE-AIMD) in the NVT ensemble at room temperature, in the presence of externally applied, uniform static electric fields of increasing intensity. The dissociation of water molecules to form chemically adsorbed species was scrutinized, in addition to charge redistribution and Grotthus proton hopping between water molecules. Dynamical properties of the adsorbed water molecules and OH– and H3O+ ions were gauged, such as the hydrogen bonds between protons in water molecules and the bridging oxygen atoms at the hematite surface, as well as the interactions between oxygen atoms in adsorbed water molecules and iron atoms at the hematite surface. The development of Helmholtz charge layers via water breakup at Fe2O3–hematite/water interfaces is also an interesting feature, with the development of protonic conduction on the surface and more bulk-like water.

Our extensive first-principles calculations reveal that the chemical activities of monolayer transition metal dichalcogenides (TMDs) MX2 (M = Mo or W, and X = Te, Se, or S) for water splitting and hydrogen evolution are modified and promoted on their grain boundaries (GBs) when in-plane tensile loadings are applied. Compared with monolayer TMDs without GBs, the flexoelectricity induced by nonuniform deformation and strain gradient significantly enhances the charge polarizations of X and M atoms at the GB sites of monolayer TMDs, which facilitates the dissociation of water molecules on the GB sites and reduces the reaction barrier of hydrogen evolution reaction. The energy barriers of splitting water molecules and hydrogen adsorption free energies on the GB sites decrease with increasing the flexoelectric effect. These results highlight an attractive way of utilizing the flexoelectric effect of GB-containing TMDs to improve their surface catalytic capability for hydrogen generation.

The preparation of high-efficiency and low-cost electrocatalysts is vital to the development of green hydrogen energy. In this study, 3D NiCu electrodes with hierarchical micro-nano structure was constructed by a simple direct-write 3D printing technology and followed by the treatment of thermal oxidation - electroreduction steps. The composite structure of Cu NWs/Cu2O and Ni/NiO in the prepared 3D NiCu promotes the dissociation of water and the conversion of hydrogen, and the special micro-nano structure displays a large active surface area. Therefore, the 3D NiCu exhibits a low overpotential of 70 mV to deliver a current density of 10 mA cm−2. It demonstrates outstanding stability in the hydrogen evolution reaction experiment for 100 h in 1 M KOH. Overall, this research provides a pioneer of modified 3D printing to hydrogen production by water electrolysis.

Oxygen deficient materials which cause the efficient splitting of water molecules has astonished the electricity generation device. This green energy harnessing device is known as hydroelectric cell. An easily processed and cost effective two stage solid-state sintering method has been opted to produce Lithium-doped SnO2 based highly efficient hydroelectric cells having no toxic by product. Structural analysis and morphological behavior of the synthesized samples were determined by the X-Ray diffraction technique and field emission scanning electron microscopy. SEM images depicted that the samples possess a highly porous nature with average grain size lying in the range 45–55 nm for all the samples. Pore volume, pore size distribution and adsorption–desorption isothermal curves were investigated using Barrett‐Joyner‐Halenda technique. All the samples exhibited mesoporous size distribution having average pore radius values 2–3 nm. Dissociation of water molecules into H3O+ and OH− ions and further ionic diffusion of these dissociated ions for the electrical energy production inside the material have been confirmed using dielectric and dc conductivity measurements of samples in both dry and hydrated conditions. Circular pellets of pure and Li-doped SnO2 samples of 2 inch diameters were fabricated to investigate the hydroelectric properties. It was observed that 15 mol% Li-doped SnO2 sample had the almost constant and sustainable current with value of 70 mA and the voltage about 0.98 V for a long duration of time. Thus, these nanostructured materials can serve as efficient and promising candidates for green energy production devices due to their high surface-to-volume ratios, exceptional charge transport features, and good physiochemical properties.

Electrocatalytic water splitting is a promising technology for large-scale hydrogen production. However, it requires efficient catalysts to overcome the large overpotentials in the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, we report a novel heterostructure catalyst Co9S8/Cu2S on copper foam (Co9S8/Cu2S/CF) with multistep impregnation and electrodeposition. Due to the strong interfacial interaction, the interfacial electrons transfer from Co sites to S sites, which promote the adsorption of oxygen-containing intermediates, water molecules, as well as the dissociation of water molecules. Therefore, the heterostructure catalyst exhibits low overpotentials of 195 mV for OER and 165 mV for HER at 10 mA cm-2, respectively. Moreover, it only needs 1.6 V to realize water splitting at 10 mA cm-2 in a two-electrode cell. This work provides an efficient method to tailor the surface electronic structure through specific morphological design and construct a heterostructure interface to achieve alkaline water splitting.

Dissociation of water molecules after soft X-ray absorption can yield neutral fragments in high-Rydberg (HR) states. We have studied the production of such fragments by field ionization and ion time-of-flight (TOF) spectrometry. Neutral HR fragments are created at all resonances below the O 1s ionization potential (IP) and particularly within 1 eV above the O 1s IP. The latter effect is due to the recapture of the O 1s photoelectrons into HR orbitals of the molecular water ion after the emission of a fast Auger electron. H₂O+(HR) fragments subsequently dissociate, yielding neutral H(HR) and O(HR) fragments, as were found by measuring the TOF spectra by pulsed field ionization. Such measurements were carried out at the O 1s → 4a₁ and 2b₂ resonances as well as just above the O 1s IP. The TOF spectra also reveal two series of oscillatory structures that are attributed to quantum beats involving Lyman emission in one of the series and field ionization of H(HR) fragments in the other series.

The article formulates a mathematical model of non-stationary transfer of 1:1 electrolyte in potentiodynamic mode, taking into account electroconvection and non-catalytic reaction of dissociation/recombination of water molecules in membrane systems, which are considered the channel of desalting of the electrodialysis apparatus. Using this model, the main regularities of the space charge distribution are theoretically established, the influence of the input parameters is determined: initial concentration, potential sweep rate, etc. It is shown that the desalination channel consists of narrow quasi-equilibrium regions of space charge adjacent to ion-exchange membranes; an electric double layer appears in the central part, caused by the recombination reaction. Regions of electroneutrality are located between this double electric layer and the near-membrane space charge regions. This study will further be used to analyze the combined effect of the noncatalytic reaction of dissociation of water molecules and recombination and electroconvection on the current-voltage characteristic of the desalting channel.

The emergence of hydrogen energy as a viable alternate source of green energy strongly adheres on designing materials for its practical storage and production. In this connection, the dissociation of water leading to the generation of hydrogen molecule is of central importance. In our current computational study employing density functional theory based methods, we explore Ti and V atom decorated boron nitride nanotube (BNNT) as a possible nanocatalyst for dissociation of water molecule and concomitant hydrogen generation. Computing the dissociation barrier of a water molecule can be a crucial parameter in deciding the efficacy of the nanostructure, and we find out the same on Ti-BNNT and V-BNNT systems to be 0.12 eV and 0.27 eV respectively. Subsequent dissociation of another water molecule leading to formation of molecular hydrogen proceeds in an almost barrier-less fashion in the case of Ti-BNNT. Stabilization of the transition state structure by hydrogen bond involving O-H···N is the possible reason for the low barrier of this process. These results seem encouraging and likely to stimulate further interest as viewed from the perspective of BNNT as semiconducting material independent of its chirality and designing such a system is practically achievable in light of some recent experimental findings.

The adsorption and dissociation of water molecules on two-dimensional transition metal dichalcogenides (TMDs) is expected to be dominated by point defects, such as vacancies, and edges. At the same time, the role of grain boundaries, and particularly, mirror twinboundaries (MTBs), whose concentration in TMDs can be quite high, is not fully understood. Using density functional theory calculations, we investigate the interaction of water, hydroxyl groups, as well as oxygen and hydrogen molecules with MoSe2 monolayers when MTBs of various types are present. We show that the adsorption of all species on MTBs is energetically favorable as compared to that on the basal plane of pristine MoSe2, but the interaction with Se vacancies is stronger. We further assess the energetics of various surface chemical reactions involving oxygen and hydrogen atoms. Our results indicate that water dissociation on the basal plane should be dominated by vacancies even when MTBs are present, but they facilitate water clustering through hydroxyl groups at MTBs, which can anchor water molecules and give rise to the decoration of MTBs with water clusters. Also, the presence of MTBs affects oxygen reduction reaction (ORR) on the MoSe2 monolayer. Unlike Se vacancies which inhibit ORR due to a high overpotential, it is found that the ORR process on MTBs is more efficient, indicating their important role in the catalytic activity of MoSe2 monolayer and likely other TMDs.

Electrochemical water splitting via a cathodic hydrogen evolution reaction (HER) is an advanced technology for clean H2 generation. Ru nanoparticle is a promising candidate for the state-of-the-art Pt catalyst; however, they still lack the competitiveness of Pt in alkaline and neutral media. Herein, a ternary HER electrocatalyst involving nano Ru and Cr2O3 as well as N-doped graphene (NG) that can work in alkaline and neutral media is proposed. Cr2O3 and NG feature strong binding energies for hydroxyl and hydrogen, respectively, which can accelerate the dissociation of water, whereas Ru has weak hydrogen binding energy to stimulate hydrogen coupling. The HER activity of Ru is greatly enhanced by the promoted water-dissociation effect of NG and Cr2O3. To achieve a current density of 10 mA cm−2, the as-obtained Ru–Cr2O3/NG only needs a very low overpotential of 47 mV, which outperforms the activity of Pt/C in alkaline media. The strategy proposed here, multi-site acceleration of water dissociation, provides new guidance on the design of a highly efficient, inexpensive, and biocompatible HER catalyst in nonacidic condition.

Facilitating the dissociation of water and desorption of hydrogen are both crucial challenges for improving the hydrogen evolution reaction (HER) in alkaline media. Herein, we report the synthesis of heterostructure of Ru2 P/WO3 @NPC (N, P co-doped carbon) by a simple hydrothermal reaction using ruthenium and tungsten salts as precursors, followed by pyrolyzing under an Ar atmosphere. The Ru2 P/WO3 @NPC electrocatalyst exhibits an outstanding HER activity with an overpotential of 15 mV at a current density of 10 mA cm-2 and excellent durability in a 1.0 M KOH solution, outperforming state-of-the-art Pt/C and most reported electrocatalysts. Experimental results combined with density functional calculations reveal that the electron density redistribution in Ru2 P/WO3 @NPC is achieved by electron transfer from NPC to Ru2 P/WO3 and from Ru2 P to WO3 , which directly promotes the dissociation of water on W sites in WO3 and desorption of hydrogen on Ru sites in Ru2 P.

X-ray, energetic photon, and electron irradiation can ionize and electronically excite target atoms and molecules. These excitations undergo complicated relaxation and energy-transfer processes that ultimately determine the manifold system responses to the deposited excess energy. In weakly bound gas- and solution-phase samples, intermolecular Coulomb decay (ICD) and electron-transfer-mediated decay (ETMD) can occur with neighboring atoms or molecules, leading to efficient transfer of the excess energy to the surroundings. In ionic solids such as metal oxides, intra- and interatomic Auger decay produces localized final states that lead to lattice damage and typically the removal of cations from the substrate. The relative importance of Auger-stimulated damage (ASD) versus ICD and ETMD in microsolvated nanoparticle interfaces is not known. Though ASD is generally expected, essentially no lattice damage resulting from the ionization and electronic excitation of microsolvated boehmite (AlOOH) nanoplatelets has been detected. Rather efficient energy transfer and soft ionization of interfacial water molecules has been observed. This is likely a general phenomenon at gas-oxyhydroxide nanoparticle interfaces where the density of states of the ionized chemisorbed species significantly overlaps with the core hole states of the solid.

Non-precious metal-based electrocatalyst with high activity and stability for efficient hydrogen evolution reaction (HER) is of critical importance toward low-cost and large-scale water splitting. Traditional MoS2 has electrocatalytic hydrogen evolution inertness in alkaline environment, which is detrimental to the adsorption and dissociation of water. Composited with electrocatalyst with good electrical conductivity can enhance its HER activity. In this work, we for the first time construct a carbon-supported hollow heterostructure MoS2@Mo2C composite via two-step calcination and sulfurized process from carbonized Mo2C–Mo3C2 heteronanowires. The results show that the existence of the Mo3C2 phase is the key point to construct the effective heterostructure with hollow morphology. Due to the strong negative hydrogen binding energy for H on surface of Mo2C, the H+ reduction in the MoS2@Mo2C in the Volmer step can be enhanced. Compared with MoS2, MoS2@Mo2C has high electrocatalytic activity for hydrogen evolution with an onset potential of 28 mV, overpotential of 129 mV at the current density of 10 mA cm−2, a small Tafel slope of 78 mV dec−1, and an excellent stability. This work will provide new insights into the design of high-efficiency HER catalysts via interfacial engineering at nanoscale for commercial water splitting.

The interactions of water vapor with rare earth oxide surfaces play a major role in many important practical processes, such as heterogeneous catalysis and corrosion phenomena, especially for “real...

The degradation of catalysts for CO oxidation in humid air is a common issue owing to the blocking of the active site by the adsorption and dissociation of water molecules. In order to evaluate the effect of humidity on the CO oxidation, the adsorption and dissociation of the common gas molecules in air, namely CO, O2, H2O, and N2, on single Ni-embedded divacancy graphene (Ni-DG) have been investigated using first-principles calculations. It was found that all the molecules keep their molecular state and the adsorption energy of CO is much larger than those of the other molecules. In addition, the CO molecules can sufficiently substitute the pre-adsorbed O2, H2O, and N2 molecules with small energy barriers, indicating that the active site of the Ni-DG will not be blocked by water molecules in humid environments. At most two CO molecules can be chemically adsorbed on the Ni-DG, indicating that a new termolecular Eley–Rideal (TER) mechanism is preferred, and the energy barrier for the rate-limiting step (2CO + O2 → OCOOCO) is only 0.34 eV. Hirshfeld charge analysis shows that the charge transfer from the O2-2π* orbital to the CO-2π* orbital plays an important role in the CO oxidation via the TER mechanism. Overall, our results show that the low-cost Ni-DG is an efficient catalyst for CO oxidation, even in humid air at low temperature.

Plasma interaction with water results in the dissociation of water (H 2 O) molecules leading to the formation of oxidative and reductive species such as hydroxyl radicals (•OH), hydrogen peroxide (H 2 O 2 ), atomic oxygen (O), atomic hydrogen (H), molecular hydrogen (H 2 ), and aqueous electrons. The reactive species generated are responsible for degradation of toxic chemicals such as PFOA. In our previous study 1 , we analyzed mineralization of 50 ppm PFOA with a gas-liquid plasma reactor using nanosecond pulses and varying the pulse frequency between 0.25kHz - 10kHz. The highest F - production rate of 1.57×10 -8 moles/s was observed at 5 kHz. The highest energy efficiency of 9.12×10 -9 moles/J was observed at 0.25 kHz.

Al-water reaction promoted by catalysts is a promising hydrogen generation technology. In this work, a high-activity M-B/γ-Al2O3 (M = Co, Ni) catalyst is prepared by wet chemical reduction method. It is found that M-B/γ-Al2O3 catalyst significantly promotes the Al-water reaction and decreases the induction time. When the molar ratio of γ-Al2O3 to Co-M in Co–B/γ-Al2O3 catalyst is 1:1, the induction time is only 0.43 h. The catalytic activity of M-B/γ-Al2O3 is proportional to its active area. SEM analyses show that M-B particles are dispersed on γ-Al2O3 surface, which reduces the agglomeration of M-B and increases the active surface of M-B/γ-Al2O3, leading to a high catalytic activity. A possible mechanism is proposed, which shows that the dissociation of water molecules on γ-Al2O3 surface and the microgalvanic interaction between M-B and Al can promote the hydration process of passive oxide film on Al particle surface, speeding up the Al-water reaction.

The interfacial interaction of U3Si2 with water leads to corrosion of nuclear fuels, which affects various processes in the nuclear fuel cycle. However, the mechanism and molecular-level insights into the early oxidation process of U3Si2 surfaces in the presence of water and oxygen are not fully understood. In this work, we present Hubbard-corrected density functional theory (DFT + U) calculations of the adsorption behavior of water on the low Miller indices of the pristine and defective surfaces as well as water dissociation and accompanied H2 formation mechanisms. The adsorption strength decreases in the order U3Si2{001} > U3Si2{110} > U3Si2{111} for both molecular and dissociative H2O adsorption. Consistent with the superior reactivity, dissociative water adsorption is most stable. We also explored the adsorption of H2O on the oxygen-covered U3Si2 surface and showed that the preadsorbed oxygen could activate the OH bond and speed up the dissociation of H2O. Generally, we found that during adsorption on the oxygen-covered, defective surface, multiple water molecules are thermodynamically more stable on the surface than the water monomer on the pristine surface. Mixed molecular and dissociative water adsorption modes are also noted to be stable on the {111} surface, whereas fully dissociative water adsorption is most stable on the {110} and {001} surfaces.

Interfacial adsorption and dissociation of water molecules at the α-Al2O3(0001) surface were studied using a novel hybrid 2D-periodic Self-Consistent Charge Density Functional Tight-Binding/Molecular Mechanics Molecular Dynamics (SCC-DFTB/MM MD) simulation strategy. The (0001) surface of α-Al2O3 (C-plane) was considered to assess the structural and dynamical behavior of adsorbed water at the interface region. In-plane distribution profiles of oxygen and hydrogen with respect to the non-periodic z-coordinate provide detailed information on the ordering of monolayer adsorbed water molecules at the interface. Dissociation of water molecules occured on the picosecond time scale, indicated by the formation of an additional plane-H peak located at 0.056 nm. Along simulation 4.2 OH groups per nm2 were formed at the α-Al2O3(0001) surface.

Water-molecule channeling in bundles of carbon nanotubes in the presence of vacancies on walls and adsorbed atoms inside the tube is studied using the computer-simulation method. Estimation calculations show that channeling in the intertube space or dechanneling lead to the fast dissociation of water molecules. Therefore, studying the channeling process in bundles can be reduced to considering channeling in an individual carbon nanotube. It is shown that a change in the parameters of the beam of passed particles makes it possible to discover structural damage done to the bundles of nanotubes. A comparison with analogous results on a hydrogen atom and molecule channeling is made. It is discovered that the use of triatomic molecule channeling to study bundles of carbon nanotubes makes it possible to reveal structural imperfections, such as atoms adsorbed inside the tubes or vacancies on the walls, with a high effectiveness.

Dissociative adsorption of water molecules on silicene is an efficient way to open the band gap of silicene for electronic applications. However, the dissociation of H2O molecules on silicene is di...

The paper reports synthesis of CdS supported rGO where reduction of GO to rGO was carried out electrochemically in situ. This catalyst had a better activity for photo-electrochemical dissociation of water to hydrogen. Catalysts were characterized by XRD, FTIR, DRS, XPS, EIS and Mott-Schottky analysis. It is reported that this catalyst showed formation of heterojunction at the interface of CdS and rGO by chemical interaction between the two. This resulted in a greater band bending, a higher charge carrier density, low resistance for electronic mobility and low recombination rate. A better activity of the catalyst is due to the above mentioned attributes.

Proton transfer and hydrogen-bonding networks are critical in biochemical processes including protein folding and protein–protein interactions. Surface science can simplify these complex systems by studying the exchange of hydrogen and deuterium atoms between molecules supported on surfaces. Temperature programmed desorption (TPD) was used to show that the exchange of hydrogen and deuterium between co–adsorbed isotopologues of ethanol and water occurs readily at temperatures below 200 K on Au(111). Since Au(111) is an inert substrate that does not cause dissociation of water or ethanol at any temperature, the results herein suggest that Au(111) acts as a support to facilitate H/D exchange via hydrogen-bonded networks of molecular ethanol and water at low temperatures.

Encapsulation of a functional organic dye in a rigid host is a viable approach to obtain a chemically stable water sensor. This study employed a H+-sensitive organic dye encapsulated in a zeolite, AlPO4-5, for the detection of atmospheric moisture and trace water in various organic solvents. AlPO4-5 not only acted as the host but also facilitated the dissociation of water molecules chemisorbed in its framework. The generated H+ protonated the encapsulated azo dye, resulting in a color change that could be clearly seen with the naked eye. The water content was determined from the ratiometric change in the optical absorption of the azo dye at ∼575 and ∼465 nm. A high sensitivity, broad detection range (0.1–5 wt%), fast response (within 5 s), and multiple reusability were achieved in the colorimetric monitoring of various alcohol and non-alcohol solvents. Importantly, we demonstrated that this method has high sensitivity and comparable accuracy to the traditional Karl Fisher method. Thus, our portable and reusable sensor design can be potentially adopted for convenient industrial process and environmental monitoring.

Polyatomic molecules in strong laser fields can undergo substantial nuclear motion within tens of femtoseconds. Ion imaging methods based on dissociation or Coulomb explosion therefore have difficulty faithfully recording the geometry dependence of the field ionization that initiates the dissociation process. Here we compare the strong-field double ionization and subsequent dissociation of water (both H$_2$O and D$_2$O) in 10-fs and 40-fs 800-nm laser pulses. We find that 10-fs pulses turn off before substantial internuclear motion occurs, whereas rapid internuclear motion can take place during the double ionization process for 40-fs pulses. The short-pulse measurements are consistent with a simple tunnel ionization picture, whose predictions help interpret the motion observed in the long-pulse measurements., 9 pages, 5 figures

Since planar laser-induced fluorescence (PLIF) temperature measurements in a combustion-flow field can only be performed in regions in which OH is abundant (i.e., the reaction and high-temperature burnout zones), this paper investigates the feasibility of using photolysis of dissolved water to generate additional OH in the low-temperature and non-reaction zones of the flow field. Multi-line fluorescence showed that the generated OH had reached thermal equilibrium within 50 ns after dissociation with a fitting temperature of 300 K in room-temperature air. To further verify the technical accuracy, averaged PLIF images from dissociated OH were calibrated and compared with thermocouple measurements in a heated-flow field, and the average deviation in the 423–823 K temperature range was less than 40 K, with a relative system error better than 5%. The results of this paper confirm the feasibility and accuracy of the photo-fragment PLIF (PF-PLIF) temperature measurement in a low-temperature flow field. This makes it an effective complement to traditional PLIF measurements, with great significance for analysis and model validation of combustion processes in low temperature.

The process of non-reagent adjustment of the pH of a NaCl solution (0.5 g/L) of different acidity was investigated by the method of bipolar electrodialysis on a device operating according to the K-system (concentration). The experiments were carried out in the range pH = 2.0–12.0 with monopolar cation-exchange MK-40 (for alkaline solutions) or anion-exchange MA-40 (for acidic solutions) and bipolar MB-2 membranes. The regularities of the change in the pH of the solution on the current density, process productivity and energy consumption for the neutralization process have been investigated. Revealed: with different productivity of the apparatus (Q = 0.5–1.5 m3/h), in the range of pH 3.0–11.0, with an increase in the current density, a neutral pH value is achieved. It has been shown that at pH above 11.0 and below 3.0, even at high current densities (i &gt, 20 A/m2), its value cannot be changed. This is due to the neutralization of the H+ or OH− ions generated by the bipolar membrane by water ions, which are formed as a result of the dissociation of water molecules at the border of the monopolar membrane and the solution under conditions when the value of current exceeds the limiting value.

We calculated the adsorption of H, O, OH, and H2O and the dissociation of H2O molecule on the Cu(111), Cu(100), and Cu(110) surfaces using density functional theory. H, O, and OH tend to adsorb stably at the highly coordinated dh and h sites on the Cu(111) and Cu(100) surfaces. OH and H tend to adsorb on sb site on the Cu(110) surface. The more charge transfer of the adsorbed substance, the more stable the adsorption. The dissociation product is O+H on the Cu(111) surface, while the dissociation product is OH+H on the Cu(100) and Cu(110) surfaces. Due to the different geometric structures of initial state (IS), transition state (TS), and final state (FS) in the dissociation reaction, the dissociation of water on the copper surface does not establish a linear Bronsted-Evans-Polanyi (BEP) relationship. These results provide theoretical support for the understanding of the interaction between water and metals as well as the behavior of water molecules.

Graphical abstract, Highlights • Luminescence of *Ce3+ at Ce4+ sonoreduction by es in H2O and C2H4(OH)2 was found. • This sonochemiluminescence is quenched by the H+ ion, acceptor of a solvated electron. • Sonochemiluminescence of *Ce3+ ion is also registered in aqueous CeCl3 solutions. • In this case Ce4+ is formed at Ce3+ oxidation by OH, then reduced to *Ce3+ by eaq. • In this case the sonochemiluminescence is quenched by both H+ and Br−, OH acceptor., The moving single-bubble sonoluminescence of Ce3+ in water and ethylene glycol solutions of CeCl3 and (NH4)2Ce(NO3)6 was studied. As found, a significant part of intensity of the luminescence (100% with cerium concentration less than 10–4 M) is due to the sonochemiluminescence. A key reaction of sonochemiluminescence is the Ce4+ reduction by a solvated (or hydrated in water) electron: Ce4+ + es (eaq) → *Ce3+. Solvated electrons are formed in a solution via electrons ejection from a low-temperature plasma periodically generated in deformable moving bubble at acoustic vibrations. Reactions of heterolytic dissociation of solvents make up the source of electrons in the plasma. In aqueous CeCl3 solutions, the Ce4+ ion is formed at the oxidation of Ce3+ by OH radical. The latter species originates from homolytic dissociation of water in the plasma of the bubble, also penetrating from the moving bubble into the solution. The sonochemiluminescence in cerium trichloride solutions are quenched by the Br− (acceptor of OH) and H+ ions (acceptor of eaq). In water and ethylene glycol solutions of (NH4)2Ce(NO3)6, the sonochemiluminescence also quenched by the H+ ion. The sonochemiluminescence in CeCl3 solutions is registered at [Ce3+] ≥ 10–5 M. Then the sonochemiluminescence intensity increases with the cerium ion concentration and reaches the saturation plateau at 10–2 M. It was shown that sonophotoluminescence (re-emission of light of bubble plasma emitters by cerium ions) also contributes to the luminescence of Ce3+ in solutions with [Ce3+] ≥ 10–4 M. If the cerium concentration is more than 10–2 M, a third source contributes to luminescence, viz., the collisional excitation of Ce3+ ions penetrating into the moving bubble.

The photodouble ionization of water at about 32 eV excess energy has been investigated both experimentally and theoretically. In an energy and angular resolved photoelectron–photoelectron coincidence experiment, the two photoelectrons in unequal energy sharing (25 and 7 eV) condition, have been detected in a plane perpendicular to the propagation direction of the linearly polarized radiation. The measured angular distributions have been compared with, molecular orientation averaged, triple differential cross sections calculated with a recently developed theoretical model (Randazzo et al 2020 Phys. Rev. A 101 033407). The model uses separable products of orbitals as initial electronic state of the water molecule taken as a two-electron target and describes accurately the correlated two electron continuum. The combination of calculated cross sections corresponding to different dication states capture most of the measured features in terms of the evolution of both the shape and the intensity as a function of the faster electron direction which is set at 0°, 30° and 60° with respect to the polarization vector ε ⃗ of the incident radiation. A detailed analysis in terms of the different dication states as well as of the partial wave contributions to the electron pair wave function sheds light on the origin of such features.

A technique for simultaneous velocimetry and thermometry in intermediate temperature flow is developed by combining hydroxyl-tagging velocimetry (HTV) and two-line OH planar laser-induced fluorescence (OH-PLIF). The OH tagging particles generated in HTV from the dissociation of water vapor are then used in two-line PLIF for thermometry. Using fragmentary OH expands PLIF to thermometry in regions that lack original OH, such as low temperature or unreactive ones. Meanwhile, using the PLIF system for both velocimetry and thermometry makes for a more efficient experimental system. As a proof of concept, the temperature and velocity are measured of a heated gas mixture comprising helium and water vapor. The temperature results agree well with the thermocouple results.

The enhanced probability of water dissociation at the aqueous electrode interfaces is predicted by path-integral ab initio molecular dynamics. The ionization process is observed at the aqueous platinum interface when nuclear quantum effects are introduced in the statistical sampling, while minor effects have been observed at the gold interface. We characterize the dissociation mechanism of the formed water ions. In spite of the fact that the concentration and lifetime of the ions might be challenging to experimentally detect, they may serve as a guide to future experiments. Our observation might have a significant impact on the understanding of electrochemical processes occurring at the metal electrode surface.

Hydrogen evolution reaction (HER) is more sluggish in alkaline than in acidic media because of the additional energy required for water dissociation. Numerous catalysts, including NiO, that offer active sites for water dissociation have been extensively investigated. Yet, the overall HER performance of NiO is still limited by lacking favorable H adsorption sites. Here we show a strategy to activate NiO through carbon doping, which creates under-coordinated Ni sites favorable for H adsorption. DFT calculations reveal that carbon dopant decreases the energy barrier of Heyrovsky step from 1.17 eV to 0.81 eV, suggesting the carbon also serves as a hot-spot for the dissociation of water molecules in water-alkali HER. As a result, the carbon doped NiO catalyst achieves an ultralow overpotential of 27 mV at 10 mA cm−2, and a low Tafel slope of 36 mV dec−1, representing the best performance among the state-of-the-art NiO catalysts., While H2 evolution from water may serve as a renewable source of fuel, there are a limited number of catalysts that are stable and active in alkaline media. Here, authors find carbon doping of NiO to increase the number of favorable sites for H2 evolution and boost electrocatalytic performances.

The enhanced probability of water dissociation at the aqueous electrode interfaces is predicted by path-integral ab initio molecular dynamics. The ionization process is observed at the aqueous platinum interface when nuclear quantum effects are introduced in the statistical sampling, while minor effects have been observed at the gold interface. We characterize the dissociation mechanism and the dynamics of the formed water ions. In spite of the fact that the concentration and lifetime of the ions might be challenging to be experimentally detectable, they may serve as a guide to future experiments. Our observation might have a significant impact on the understanding of electrochemical processes occurring at the metal electrode surface.

International audience; Quantum tunneling in chemistry is often attributed to the processes at low or near room temperatures when the rate of thermal reactions becomes far less than the rate of quantum tunneling. However, in some rapid processes, quantum tunneling can be observed even at high temperatures. Herein, we report the experimental evidence for anomalous H/D kinetic isotope effect (KIE) during sonochemical dissociation of water molecule driven by 20 kHz power ultrasound measured in H 2 O/D 2 O mixtures saturated with Ar or Xe. Hydrogen released during ultrasonic treatment is enriched by light isotope. The observed H/D KIE (α=2.15-1.50) is much larger than what is calculated assuming a classical KIE for T g =5000 K (α=1.15) obtained from the sonoluminescence spectra in H 2 O and D 2 O. Furthermore, the α values sharply decrease with increasing of H 2 O content in H 2 O/D 2 O mixtures reaching a steady-state value close to α=1.50, which also cannot be explained by O-H/O-D zero-point energy difference. We suggest that these results can be understood in terms of quantum electron tunneling occurring in nonequilibrium picosecond plasma produced at the last stage of cavitation bubble collapse. Thermal homolytic splitting of water molecule is inhibited by extremely short lifetime of such plasma. On the contrary, immensely short traversal time for electron tunneling in water allows H 2 O dissociation by quantum tunneling mechanism.

PubMed: 32117866, Recently, liquefaction of biomass in subcritical water to convert it into value-added substances has been broadly attracting attention. However, there is a gap in literature about the levulinic acid, which is a high worth substance, production from biomass using subcritical water. As a green chemistry approach, decomposition of biomass could be obtained using subcritical water effectively. In this case, water uses as a solvent so that it gives a possibility to take place a reaction for the decomposition of biomass. Subcritical water, which liquid water and its temperature is higher than the normal boiling point of water, has higher ion product as well as higher concentrations of H+ and OH- ions. Additionally, it has high diffusivity, low viscosity and much lower dielectric constant. For instance, whereas dielectric constant of subcritical water is 80 at 298 K, it is 2 at 673 K. The point of this research paper is to assess the impacts of different reaction parameters on cellulose conversion as the principle segment of lignocellulosic biomasses for the production of value-added chemicals, particularly levulinic acid. Hazelnut shell waste was chosen as model biomass since hazelnut is a standout amongst the most cultivated agricultural crops in Turkey. Besides, Turkey provide 70% of the world's total hazelnut production. It was found that as reaction temperature increases, a considerable improvement on the amount of formed levulinic acid and conversion of hazelnut shell was observed. For instance, when the reaction temperature, time and acid concentration were 280 degrees C, 120 min and 50 mM, respectively, levulinic acid yield and conversion of hazelnut shell were found as 13.05 and 65.40%, respectively. Addition of H2SO4 enhanced the production of levulinic acid from waste hazelnut shell. Another method which is hybrid process could be used to produce value-added chemicals from lignocellulosic biomass. Hybrid process basically combines hydrolysis and electrolysis in subcritical water. Subcritical water has much lower dielectric constant than liquid water at ambient temperature. So, it was claimed that if constant current was applied to the reaction medium through specially designed electrodes in subcritical water environment, electrolysis could alter the hydrolysis reaction of cellulose in a way of protonation of intra-and inter-molecular hydrogen bonding around anode and as a result electrolysis in subcritical water could decrease necessary thermal energy to hydrolyze the beta(1-4) glycosidic linkage. Therefore, we developed a green hybrid process by combining hydrolysis and electrolysis in subcritical water without using any toxic, organic solvents and catalyst. Effects of especially applied current and temperature on the product distribution and conversions of cellulose were revealed and hydrothermal electrolysis reaction pathway of cellulose was proposed. The significance of the interaction indicated that, applied voltage had major impact on cellulose hydrolysis. Maximum cellulose conversion (82%) was achieved at 230 degrees C and 180 min of reaction time in 25 mM of H2SO4. Application of 8.0 V of applied voltage to the reaction medium at reaction temperature of 230 degrees C increased the TOC conversion (50.3%) with acid concentration of 25 mM in comparison with current-free experiments. Thus, the idea of electrochemically generated acid layer due to the dissociation of water around anode is supported. As future perspective, the output of the study gave an idea about converting cellulose and various biomass wastes, which may have high cellulose, content and led the way in obtaining valuable chemicals from no utilized real biomass sources such as hazelnut shell waste. The studies with other biomasses are undergoing.

Photocatalytic visible water splitting is still impeded by slow kinetics of multi-electron-driven water oxidation, fast carrier recombination and insufficient light absorption of the photocatalyst. Herein, the core-shell heterojunction BxGa1−xAs/GaAs photocatalyst exhibited a remarkably promoted activity for hydrogen generation by direct dissociation of water molecule over boron site on catalyst surface due to redistributing electron density, as well as by promotion of visible absorption and acceleration of charge separation and transfer via a built-in electric field. B0.25Ga0.75As/GaAs photocatalyst exhibited hydrogen evolution rate of 8.4 μmol during 8 h from pure water without electron donor and applied bias.

In the current investigation, reactive molecular dynamics simulation has been used to study and compare the dissociation behavior of water molecules on defect-free and defective rutile TiO2 (1 0 1) surface. According to the contour map for a water molecule on the TiO2 (1 0 1) surface, water molecules have proven to dissociate around 20 times faster in the defective surface rather than defect-free surface. In the presence of defects, the oxygen atoms near the defects have lower electrostatic potentials and therefore higher reactivity which adsorption of molecules to the defects and their vicinity increases while for the defect-free surface, water molecules are adsorbed like clusters and exhibit lower dispersion. Also investigation of the density profile has proven water molecules have better dispersion through the defective surface. Namely, presence of defects leads water molecules to be adsorbed at different spots through the surface. In addition to the density profile, dissociation of water molecules to hydroxyl groups and respective diffusion of hydrogen atoms into the surface (down to the second sub-layer) has been undertaken through inspection of contours for water molecules in the defective surface throughout the simulations.

This article is devoted to the construction of a new mathematical model, using a mathematical model of the system of Nernst-Planck-Poisson equations for electrodiffusion of four varieties of ions simultaneously (two salt ions, and H+, OH- ions) in the diffusion layer in electromembrane systems with a perfectly selective membrane and the heat equation, taking into account the Joule heating of the solution, endo- and exothermic nature of the reactions of dissociation of water molecules and recombination of ions. In addition, the model takes into account the dependence of the coefficient of equilibrium of the dissociation/recombination reaction on temperature. The mathematical model is a boundary value problem for the system of ordinary differential equations, the study of which allows determining the basic patterns of transport of ions of binary salt and water dissociation products taking into account the space charge, reactions dissociation/recombination of water and the corresponding temperature effects. The paper presents the conclusion of the formula for the amount of heat absorbed/emitted at each point $x$, during the course of the dissociation/recombination reaction of water. A boundary condition is derived at a point $x=\delta $ with allowance for the balance of heat fluxes at this point. The study determines the structure of the diffusion layer from the receiving side of the membrane, and, accordingly, the asymptotic solutions in each of the regions of the diffusion layer, to conduct their splicing. The conditions under which the practically irreversible dissociation of water with the maximum possible constant rate in the expanded space charge region are determined. In addition, the study shows that in the region of electroneutrality a narrow band (the recombination region) arises, where the recombination of water molecules prevails over their dissociation, and that the centers of the recombination and dissociation region, within the diffusion layer, are spaced from each other at a considerable distance.

Methanesulfonic acid (MSA):water-alcohol (ethanol and isopropanol) systems were studied at temperatures in the range from 295 K to 360 K using high-resolution 1H NMR and ac-impedance analyzer in order to investigate the formation of ionic charge carriers as well as their transport in these ionic mixtures and the dissociation constants. The obtained dissociation constants of MSA:water-alcohol at water-rich and alcohol-rich sides are higher than the same system without MSA due to higher protonic charge carrier concentrations facilitating the structure diffusion of protons. The dissociation constant at the water-rich side (0.63) is comparable to that at the ethanol-rich side (0.58) and slightly higher due to the higher acidity of water. Remarkably, a plateau in the molecular diffusion coefficients and ionic mobility curves is observed in the region between the water-rich side and the alcohol-rich side and the diffusion self-coefficients in the plateau are higher than everywhere else. The temperature dependence of ionic conductivity in MSA:water-alcohol is dominated by the reduction and rearrangement of the hydrogen-bond strength accompanied by a heating induced networking rather than by an ionic formation process. The degree of hydrophobicity plays a more effective rule in the self-diffusion coefficient and in the ionic conductivity compared to the degree of hydrophobicity in ethanol and isopropanol. The data are relevant for the understanding and optimization of the properties of PEM fuel cells and for polymeric ion rejection membranes which are based on sulfonic groups (-SO3H). They provide interesting insight into the water dependence of the viscoelastic and kinematic properties, the charge formation mechanism and the dissociation limit, with the presence of a hydrophobic group mimicking the ionization of water into the sulfonated polymeric membrane used in many applications such as in PEM fuel cells.

Aiming at an improved molecular scale understanding of the interaction of water with Ru surfaces and electrodes, in particular with respect to thermally induced water dissociation, we have performed a systematic study of the low temperature adsorption and structure formation behavior of water on Ru(0001) by scanning tunneling microscopy (STM). Typical structures formed upon adsorption at below 100 K indicate the presence of molecularly adsorbed water. For adsorption at 120 K, in contrast, the resulting structures are identical to phases which have been associated with partially dissociated adsorbed water, indicating that for continuous adsorption under these conditions thermally induced water dissociation is activated. This assignment is supported by the strongly hindered activity for further adsorption of H2O or CO (at 100 K) on surfaces where only half of the surface is covered by structures related to an adsorbed H2O/OH phase. This is attributed to passivation by a H adlayer on the remaining, apparently bare surface areas, which results from H2O dissociation. Consequences of these findings on the understanding of water interaction with Ru(0001) are discussed.

Rutile RuO2 is a highly active catalyst for a number of (electro)chemical reactions in aqueous solutions or in humid environments. However, the study of the interaction of RuO2 surfaces with water has been confined largely to the ultra-high vacuum environment, and to the thermodynamically stable (110) surface. In this work, we combine ambient pressure X-ray photoelectron spectroscopy, in situ surface diffraction and density functional theory calculations to investigate how four different facets of RuO2 interact with water under humid and electrochemical environments. The vacant coordinatively unsaturated Ru site (CUS) allows for the adsorption and dissociation of water molecules. Different surfaces exhibit unique binding energetics for -H2O and -OH and can allow for different degrees of hydrogen bonding between the adsorbates. Consequently, the degree of water dissociation is found to be sensitive to the surface crystallographic orientation - being maximum for the (101) surface, followed by the (110), (001) and (100) surfaces. This study identifies crystallographic orientation as an important parameter to tune not only the density of active sites but also the energetics for water dissociation; this finding is of great significance for many catalytic reactions, where water is a key reactant, or product.

Plasma–liquid interactions have gained escalated interests over the last decade due to their potentials in many applications. The simultaneous generation of physicochemical phenomena of interest promotes itself to the top of the promising technologies for liquid processing. Here, we study the physics of a microwave plasma jet (MWPJ) submerged into water and its feasibility to wastewater treatment. We investigate the plasma and bubble dynamics using high-speed imaging. The effects of the argon flow rate, additive gas, and microwave power on the dynamics are examined highlighting the retreating behaviors of plasma channels due to the losses of electrons and power caused by nearby water surface. The addition of N2 (

A thin-layer of Ni(OH)2 was in situ formed on the surface of Ni2P nanopillars (Ni(OH)2@Ni2P/E-NF) via a facile hydrothermal treatment in H2O. Ni(OH)2@Ni2P/E-NF exhibits superior activity for the hydrogen evolution reaction with an overpotential of only 43 mV to achieve 10 mA cm−2 and a good durability during the long-term operation in an alkaline medium. The excellent performance of Ni(OH)2@Ni2P/E-NF is likely ascribed to the strong interfacial coupling of Ni(OH)2 and Ni2P, which promotes the dissociation of water and concomitantly converts hydrogen intermediates (Had) to H2. Keywords: Nickel hydroxide, Nickel phosphide, Etching, Hydrogen evolution reaction

peer-reviewed The full text of this article will not be available in ULIR until the embargo expires on the 18/06/2019 The high reactivity of lithium with gas molecules under ambient conditions plays a key role, negative or positive, depending on the purpose, in its wide applications. However, the underlying mechanism is still unclear. A facilitated dissociation of water in the presence of lithium (Li) under ambient conditions is revealed using molecular simulations. The subsequent reactions with other gases are investigated to elucidate the role of water in enabling lithium–gas reactions. The in-depth understanding of controlled lithium reactively opens up a new avenue of designing highly selective gas separation processes. A controlled exclusive reaction of lithium with nitrogen in the nitrogen/methane mixture would provide infinite selectivity of nitrogen over methane, revolutionizing the natural gas purification industry.

It is crucial to control the O–H bond cleavage on metal surfaces with preadsorbed potassium atoms in heterogeneous catalysis. On the basis of the density functional theory (DFT) calculations, the adsorption and dissociation of water on clean and potassium preadsorbed transition metal surfaces, including group 11 (Cu, Ag, and Au) and group 8–10 metal (Co, Ni, Ru, Rh, Pd, Ir, and Pt) surfaces, have been investigated systematically. The calculation results show that the presence of potassium atom enhances the binding strength of H2O but weakens the binding strength of OH. More importantly, it was found that the preadsorbed potassium can promote the catalytic activity of various metals for H2O dissociation to varying degrees and the more promoting effect of potassium on the water O–H bond scission occurs on the less chemically active transition metals. On the basis of electronic and geometric analysis, the physical origin of the promotion effect can be attributed to the dipole–dipole interactions like ((Kδ+-O...