H2O Reaction Research Articles

Effect of the PH2O/PCO2 and PH2 on the intrinsic electro-catalytic interactions and the CO production pathway on Ni/GDC during solid oxide H2O/CO2 co-electrolysis

The study presents a holistic methodology for the discrimination of the contribution of H2O and CO2 electrolysis reactions, as well as of the RWGS, on the production rate of CO during the solid oxide H2O/CO2 co-electrolysis process. The investigation took place on an electrolyte supported cell with Ni/GDC as the fuel electrode, at 800–900 °C, by applying various PΗ2Ο/PCO2 feed ratios, in the range of 0 ≤ PΗ2Ο/PCO2 ≤ 1, and two PΗ2 values (2 and 21 kPa). Critical combination of physicochemical and electrochemical characterization with electrocatalytic measurements and quantitative analysis of products highlighted a competitive adsorption and electro-reduction between H2O and CO2 on Ni/GDC. Moreover, it is confirmed that the H2O/CO2 co-electrolysis process is determined by: (i) PH2O/PCO2 ratio and (ii) PH2. Specifically, at PΗ2Ο/PCO2 = 1 and high PΗ2 = 21 kPa the adsorption of H2O is favored, compared to CO2, and the electrochemical process is 100% selective towards the electrolysis of H2O. The CO production is catalytically controlled by the RWGS reaction. The electrochemical reduction of CO2 occurs at PΗ2Ο/PCO2 = 0.3, in combination with H2O electrolysis and the RWGS, whereas its contribution is enhanced by decreasing the PΗ2Ο and PΗ2.

Enhanced overall water splitting under visible light of MoSSe∣WSSe heterojunction by lateral interfacial engineering

Photocatalytic splitting water is a promising method to obtain hydrogen energy. While design and synthesis of efficient and economical photocatalysts is one of the important contents. Janus MoSSe and WSSe monolayers are efficient and wide sunlight harvesting photocatalysts due to their intrinsic vertical electric fields. So how is the photocatalytic performance of lateral MoSSe∣WSSe heterojunctions, which possesses an intra-plane interface and intrinsic vertical electric field? In the present work, the structural property, electronic characteristic, optical property, and photocatalytic application of MoSSe∣WSSe lateral heterojunctions are systematically investigated. It is found that both zigzag and armchair configurations are semiconductors with suitable bandgaps of ∼1.60 eV. Besides, they possess a type-II band alignment where electrons tend to accumulate at the coupling interface of MoSSe side and holes at WSSe side, giving rise to a paralleled electric field in heterojunctions, which can largely promote the separation of photo-generated carriers. More remarkably, these heterojunctions exhibit pronounced solar-spectrum absorption efficiency, proper valence, and conduction band positions by initializing the redox reactions of H2O and high carrier mobility. Intriguingly, the zigzag MoSSe∣WSSe heterojunction has a better photocatalytic performance in an acidic environment, and the armchair MoSSe∣WSSe prefers to produce H2 and O2 in a neutral environment. These fascinating properties render the intra-plane MoSSe∣WSSe heterojunctions as the wide solar harvesting photocatalysts in further overall water splitting.

XPS and FTIR investigations of the transient photocatalytic decomposition of surface carbon contaminants from anatase TiO2 in UHV starved water/oxygen environments

This paper explores the transient photocatalytic oxidation mechanism of carbon contaminants from a high surface area anatase TiO2 pellet under starved water/oxygen reaction conditions created when specimens are irradiated via a 375 nm UV laser inside the UHV analysis chamber of an XPS spectrometer. Complementary results are also provided following similar UV irradiations and reaction procedures in an evacuated in situ reaction cell of a Fourier-transform infrared spectrometer (FTIR). An interactive and non-steady state transient photocatalytic reaction is observed between surface carbon species and strongly adsorbed H2O brought to the exterior surface of the pellet via UV photodesorption from within the deeper lying pores of the pellet. The reaction stoichiometry and quantum efficiency of the reaction are reported at various irradiation intensities. In situ FTIR spectral features are also presented and discussed for a non-UV treated TiO2 sample and a 2-hour UV-treated TiO2 sample under evacuated conditions also showing the decomposition of carbon contaminants species and the consumption of adsorbed water/hydroxyls with the ensuing formation of carboxyl (HO-CO) carbon species and isolated surface hydroxyls. The photocatalytic decomposition of carbon species and the concomitant consumption of oxygen containing species was also tracked by following the XPS spectral changes of a UV-irradiated area on the pellet surface compared to a dark reference spot on the same specimen. Eight different reaction cases at four different UV intensities, repeated twice each, were also investigated using separate pieces of the same TiO2 media. The measured stoichiometry for the decomposition of carbon species and consumption of oxygen ranged from 0.53 during the first 10–20 min of irradiation and increased to 0.65 with an average value of 0.59 and a standard deviation of 0.11. These data suggest that the reaction product and leaving group from the TiO2 surface is primarily CO2 during the first 10–20 min of initial reaction with perhaps a small fraction of CO toward the end of reaction. Heating the sample specimen to 100 °C for 2-hour inside the XPS-UHV analysis chamber prior to UV illumination was effective in eliminating photocatalytic oxidation and carbon removal from the surface thereby demonstrating that strongly adsorbed water (prior to heating in vacuum) was a critical and limiting reagent in the overall H2O transport and reaction process.Photon efficiencies for the reaction were calculated based on the number of carbon species removed from the XPS-observable surface versus the number of the UV photons adsorbed in the topmost 2 nm of the sample. The highest photon efficiency observed was 0.0186 after 5–10 min of UV exposure at 1.5 mW/cm2. All reaction cases showed a significant efficiency drop after 30 min of UV irradiation due to the consumption of the adsorbed reactants, both carbon and water. From detailed deconvolution of the XPS C 1s spectra, UV irradiation showed a high selectivity towards hydrocarbon contaminant decomposition, which was 75% ± 5% of all carbon species removed.

Holmium (Ho) oxide, carbide, and dioxide cation bond energies and evaluation of the Ho + O → HoO+ + e- chemi-ionization reaction enthalpy.

Guided ion beam tandem mass spectrometry (GIBMS) and quantum chemical calculations are employed to evaluate the title chemi-ionization reaction with holmium. Exchange reactions of Ho+ with O2, CO, and SO2 and HoO+ with CO, as well as collision-induced dissociation (CID) reactions of HoO+ with Xe, O2, and CO, were performed using GIBMS. Formation of HoO+ is exothermic in reactions with O2 and SO2 but endothermic for reaction with CO, as is the exchange reaction of HoO+ with CO. Quantitative analysis of these reactions and the three CID reactions provides a robust method to determine the bond dissociation energy (BDE) of Ho+-O, 6.02 ± 0.13eV. BDEs for Ho+-C and OHo+-O are also measured as 2.27 ± 0.19 and 2.70 ± 0.27eV, respectively. All three measurements are the first direct determinations of these BDEs. By combining the BDE of HoO+ with the well-established ionization energy of Ho, the exothermicity of Ho in the title chemi-ionization reaction can also be obtained as 0.00 ± 0.13eV. All experimental thermochemistry was then compared to quantum chemical calculations for the purpose of establishing benchmarks and validation. BDEs determined via these calculations are in agreement with the experiment within the inherent experimental and theoretical uncertainties, with results obtained at the coupled-cluster with single, double, and perturbative triple excitations, CCSD(T), using all-electron basis sets yielding the most accurate results.

Controllable synthesis of nanosheet-induced 3D hierarchical Zn2(OH)3VO3 with gradually enhanced electrochemical performance

Three-dimensional hierarchical mixed transition metal compounds (MTMCs) assembled by two-dimensional (2D) nanosheets hold great potential as high-performance electrode materials. Despite the abundant reserve and multi-type valence states of vanadium (V), constructing V-based MTMCs with 2D subunits still remains great challenges. Here, we reported a facile one-step hydrothermal approach to fabricate hierarchical flower-like Zn2(OH)3VO3 with highly uniform morphology and diameter, which are assembled by 2D nanosheets with average thickness of 20 nm. Appropriate amount of NH3•H2O and adequate reaction time are critical for obtaining the hierarchical Zn2(OH)3VO3 microflowers with high crystalline. Combining the large active surface area of 2D nanosheets, porous structure of 3D hierarchical microflowers, and multiple reaction mechanism of Zn2(OH)3VO3, the as-prepared hierarchical Zn2(OH)3VO3 manifests excellent lithium storage properties in term of stable cycling performance up to 3000 cycles and good rate capability. Moreover, systematical analyzes based on cyclic voltammetry, electrochemical impedance spectroscopy, and ex-situ XRD indicate that newly emerged redox, accelerated kinetics, and gradually enhanced utilization of active sites originating from the electrode activation should account for the gradually increased capacity upon cycling.

Columnar nitrogen-doped ZnO nanostructured thin films obtained through atomic layer deposition

The present study was aimed to develop nitrogen-doped nanostructured ZnO thin films. These films were produced in a sequential procedure involving the atomic layer deposition technique, and a hydrothermal process supported by microwave heating. Employing the atomic layer deposition technique, through self-limited reactions of diethylzinc (DEZn) and H2O, carried out at 3.29 × 10−4 atm and 190 °C, a high-quality ZnO seed was grown on a Si (100) substrate, producing a textured film. In a second stage, columnar ZnO nanostructures were grown perpendicularly oriented to the silicon substrate on those films, using a solvothermal process in a microwave heating facility, employing Zn(NO3)2 as zinc precursor, while hexamethylenetetramine (HMTA) was used to produce the bridging of Zn2+ ions. The consequence of N-doping concentration on the physicochemical properties of ZnO thin films was studied. The manufactured films were structurally analyzed by scanning electron microscopy and x-ray diffraction. Also, x-ray photoelectron spectroscopy, Raman, and UV–vis spectroscopies were used to provide further insight on the effect of nitrogen doping. The N-doped films displayed textured wurtzite-like structures that changes their preferential growth from the (002) to the (100) crystallographic plane, apparently promoted by the increase of nitrogen precursor. It is also shown that nitrogen-doped films undergo a reduction in their bandgap, compared to ZnO. The methodology presented here provides a viable way to perform high-quality N-ZnO nanostructured thin films.

A high activity Al–Bi@C for hydrogen generation from Al-water reaction

A high activity carbon-loaded Bi (Bi@C) is synthesized by carbonizing a home-made Bi metal coordination compound. The results show that Bi@C effectively catalyzes the Al–H2O reaction. Al–Bi@C composites are prepared by ball milling (named as Al–Bi@Cmilled) or ball milling and spark plasma sintering (SPS) (named as Al–Bi@CSPS). It can be found that the Al–Bi@CSPS obtained by sintered Al–Bi@Cmilled is converted from a powder to a block, which is beneficial for its practical application. Furthermore, the hydrogen generation performance of Al–Bi@CSPS is superior to that of Al–Bi@Cmilled. Such as the hydrogen yield of Al-5 wt% Bi@CSPS is higher than that of Al-5 wt% Bi@Cmilled (1292.0 mL g−1 vs 463.8 mL g−1), and Al-5 wt% Bi@CSPS also exhibits an excellent antioxidant ability. These results demonstrate that the SPS process is beneficial. The improvement mechanism of SPS on Al–Bi@C composites is studied by XRD, Raman spectroscopy, SEM-EDS and TEM. The fabricated Al–Bi@CSPS is expected to have practical application in the field of hydrogen supply.

Performance study on simultaneous tar removal and bio-syngas methanation by combining catalysis with nonthermal plasma

In this work, simultaneous toluene removal and syngas methanation using the combination of packed-bed dielectric barrier discharge and Ni/γ-Al2O3 catalyst were conducted with the research object of simulated gasification gas (SGG) containing toluene. The effects of reaction temperature, H2/CO ratio and H2O addition on the reaction performances of both toluene removal and SGG methanation were investigated. The results show that high-efficiency simultaneous toluene removal and SGG methanation can be achieved at 400°C under plasma catalysis treatment. When the H2/CO is 3.2, the toluene removal rate and the tar removal rate are close to 100% and 97%, the CO conversion rate and CH4 selectivity approach about 88% and 97%, and the energy efficiencies in toluene removal and SGG methanation processes can reach 9.7 g/(kW·h) and 17.3 mol/(kW·h). Both the high H2/CO ratio and the H2O addition can promote toluene removal and SGG methanation, and reduce the amount of carbon deposition but increase its graphitized degree. Moreover, high H2/CO ratio can rise the heating value of SGG and achieve higher energy efficiencies in both toluene removal and SGG methanation processes, while the H2O addition is difficult to obtain high CH4 selectivity to increase the heating value and is not conducive to the promotion of energy efficiency in SGG methanation process. In addition, for these two simultaneous processes, the SGG methanation process exerts a significant inhibiting effect on toluene removal, but process of toluene removal has less influence on the other process due to the lower concentration of toluene.

Electrochemical Oscillations (Named Oscillations H and K) during H2O2 Reduction on Pt Electrodes Induced by a Local pH Increase at the Electrode Surface

The reduction of H2O2 on Pt electrodes in H2SO4 solution shows various electrochemical oscillations, named sequentially from A to J, as reported previously. The present work demonstrates that this electrochemical system also shows a new type of oscillation, called oscillation K, when an alkali metal sulfate is added to the H2SO4 solution containing H2O2. In the presence of alkali metal ions, the local pH at the electrode surface (pHs) becomes basic during H2O2 reduction, and, consequently, reduction and oxidation reactions of HO2 −, which is formed by dissociation of H2O2, take place at the electrode. Detailed studies reveal that oscillation K is caused by an N-shaped negative differential resistance (N-NDR) that is induced by the autocatalytic reduction of HO2 − and that the oscillation can be classified as a “hidden” N-NDR (HN-NDR) type. In this sense, oscillation K is similar to oscillation H which is induced by the autocatalytic reduction of H2O2 and is an HN-NDR oscillator. Besides, a numerical simulation was conducted to understand how HO2 − reduction and oxidation cause oscillation K. To estimate the change in pHs, our simulation employs a newly developed model in which the dissociation of water and that of H2O2 at the electrode are considered.

Dynamical investigations of the O(3P) + H2O reaction at high collision energies on an accurate full-dimensional potential energy surface

The reaction between O(3P) and H2O is of significance in combustion, atmospheric and interstellar chemistry. Using an accurate full-dimensional potential energy surface (PES) for the lowest triplet state of the H2O2 system, the quasi-classical trajectory method is employed to run dynamical simulations between O(3P) and H2O at hyperthermal collision energies of 50–100 kcal mol−1, which may access the hydrogen abstraction channel OH + OH, the hydrogen elimination channel H + HO2 and the oxygen exchange channel O + H2O. The integral cross sections (ICSs), differential cross sections, product energy/state distributions and reaction mechanisms are studied for the channels leading to products OH + OH and H + HO2.

A Dual Reactor for Isothermal Thermochemical Cycles of H2O/CO2 Co-Splitting Using La0.3Sr0.7Co0.7Fe0.3O3 as an Oxygen Carrier

Catalytic performance of La0.3Sr0.7Co0.7Fe0.3O3 (LSCF3773 or LSCF) catalyst for syngas production via two step thermochemical cycles of H2O and CO2 co-splitting was investigated. Oxygen storage capacity (OSC) was found to depend on reduction temperature, rather than the oxidation temperature. The highest oxygen vacancy (Δδ) was achieved when the reduction and oxidation temperature were both fixed at 900 °C with the feed ratio (H2O to CO2) of 3 to 1, with an increasing amount of CO2 in the feed mixture. CO productivity reached its plateau at high ratios of H2O to CO2 (1:1, 1:2, and 1:2.5), while the total productivities were reduced with the same ratios. This indicated the existence of a CO2 blockage, which was the result of either high Ea of CO2 dissociation or high Ea of CO desorption, resulting in the loss in active species. From the results, it can be concluded that H2O and CO2 splitting reactions were competitive reactions. Ea of H2O and CO2 splitting was estimated at 31.01 kJ/mol and 48.05 kJ/mol, respectively, which agreed with the results obtained from the experimentation of the effect of the oxidation temperature. A dual-reactors system was applied to provide a continuous product stream, where the operation mode was switched between the reduction and oxidation step. The isothermal thermochemical cycles process, where the reduction and oxidation were performed at the same temperature, was also carried out in order to increase the overall efficiency of the process. The optimal time for the reduction and oxidation step was found to be 30 min for each step, giving total productivity of the syngas mixture at 28,000 μmol/g, approximately.

Theoretical study on the reaction of ketene + HO2: From electronic structure to model applications

Reaction kinetics study of ketene + hydroperoxyl radical (HO2) and its applications into model prediction for ketene oxidation have been investigated in this work. Potential energy surfaces (PESs) for key reactions have been obtained by employing ROCCSD(T)/CBS//BH&HLYP/6–311++G(d,p) methods. The RRKM/Master Equation was solved to calculate the temperature and pressure dependent rate constants for the title reaction pathways. Temperature-dependent thermochemistry data for ketene + HO2 radical system has also been studied. The bimolecular pathways forming HCHO + CO + OH, oxiranone + OH and acetyl radical + oxygen were found to be dominant at high temperatures. Rate constants and thermodynamics data have been incorporated into the ketene mechanism from Konnov's group (A.S. Savchenkova et al., Combust. Flame, 218 (2020) 28-41) to investigate their influence on the performance of ketene oxidation. Sensitivity and flux analysis were also carried out at 850 K to investigate the kinetics behavior of ketene + HO2 reaction system at intermediate temperatures. This work provides a better understanding of ketene oxidation and reactions between oxygenated hydrocarbons and hydroperoxyl radical.

Numerical Simulations of the Influence of Inert Gases (N2/CO2) on Combustion Characteristics of Laminar-Premixed Biosyngas Flame.

In this work, the influence of different N2/CO2 contents (up to 60% in fuel volume) on combustion features of laminar-premixed CO/CH4/H2 flame with various equivalence ratios (0.6–1.6) at standard conditions was numerically calculated using ANSYS CHEMKIN-PRO with the GRI-Mech 3.0 mechanism. The mole fraction profiles of the major species and the rate of production of dominant elementary reactions in the flames of CO/CH4/H2/N2/CO2/air were obtained. The effect of inert gas addition on the formation of NOX, H, O, and OH was analyzed, and the sensitivity coefficient of the active radical mole fraction was obtained. The results suggest that the addition of inert gas of the fuel mixture with various equivalence ratios reduces laminar burning velocity and adiabatic temperature, which have always had a good positive correlation and the maximum peak point shifted left. CO2 has obvious inhibitory effect on the formation of NO by reducing the amount of O radicals and obstructing the conduct of the reaction of NNH + O ⇔ NH + NO, but it promotes the formation of NO2 mainly through the reaction HO2 + NO ⇔ NO2 + OH. The reactions H + O2 + H2O ⇔ HO2 + H2O, H + O2 ⇔ O + OH, and OH + CO ⇔ H + CO2 are three very important reactions for the molar fractions of H, O, and OH that decrease significantly with an increase of inert gas concentration.

Atmospheric Kinetics: Bimolecular Reactions of Carbonyl Oxide by a Triple-Level Strategy.

Criegee intermediates in the atmosphere serve as oxidizing agents to initiate aerosol formation, which are particularly important for atmospheric modeling, and understanding their kinetics is one of the current outstanding challenges in climate change modeling. Because experimental kinetics are still limited, we must rely on theory for the complete picture, but obtaining absolute rates from theory is a formidable task. Here, we report the bimolecular reaction kinetics of carbonyl oxide with ammonia, hydrogen sulfide, formaldehyde, and water dimer by designing a triple-level strategy that combines (i) benchmark results close to the complete-basis limit of coupled-cluster theory with the single, double, triple, and quadruple excitations (CCSDTQ/CBS), (ii) a new hybrid meta density functional (M06CR) specifically optimized for reactions of Criegee intermediates, and (iii) variational transition-state theory with both variable rection coordinates and optimized reaction paths, with multidimensional tunneling, and with pressure effects. For (i) we have found that quadruple excitations are required to obtain quantitative reaction barriers, and we designed new composite methods and strategies to reach CCSDTQ/CBS accuracy. The present findings show that (i) the CH2OO + HCHO reaction can make an important contribution to the sink of HCHO under wide atmospheric conditions in the gas phase and that (ii) CH2OO + (H2O)2 dominates over the CH2OO + H2O reaction below 10 km.

Atomic-scale mixing between MgO and H2O in the deep interiors of water-rich planets

Water-rich planets exist in our Solar System (Uranus and Neptune) and are found to be common in the extrasolar systems (some of the sub-Neptunes). In conventional models of these planets a thick water-rich layer is underlain by a separate rocky interior. Here we report experimental results on two rock-forming minerals, olivine ((Mg,Fe)2SiO4) and ferropericlase ((Mg,Fe)O), in water at the pressure and temperature conditions expected for the water-rich planets. Our data indicate a selective leaching of MgO, which peaks between 20 and 40 GPa and above 1,500 K. For water-rich planets with 1–6 Earth masses (>50 wt% H2O), the chemical reaction at the deep water–rock interface would lead to high concentrations of MgO in the H2O layer. For Uranus and Neptune, the top ~3% of the H2O layer would have a large storage capacity for MgO. If an early dynamic process enables the rock–H2O reaction, the topmost H2O layer may be rich in MgO, possibly affecting the thermal history of the planet.

Thermodynamic simulation of metal behaviors in Cu2+-Ni2+-NH3-NH4+-C2O42--H2O system

To investigate the behaviors of Cu2+ and Ni2+ with the change of conditions in Cu2+-Ni2+-NH3-NH4+- C2O42--H2O reaction system, mathematical models of thermodynamics based on the principle of mass conservation were established. The simulation results indicate that the precipitation of metal ions from the aqueous phase is a complicated dynamic equilibrium process, during which the coordination reactions of Cu2+ and Ni2+ with NH3 forming [Cu(NH3)n]2+ (n=3-5) and [Ni(NH3)m]2+ (m=3-6) are predominant under high pH conditions, respectively. The pH ranges for the simultaneous precipitation of Cu2+ and Ni2+ are 2.0-6.5 and 2.0-5.5 when [NH3]T equals 0.6 and 4.2 mol/L, respectively, with the prefixed [C2O42-]T of 0.6 mol/L. Due to the fractional precipitation of Cu2+ and Ni2+, Cu-Ni composite is obtained after the thermal decomposition of Cu-Ni oxalate complex salts prepared in a pure water system when pH>7.0. By applying the mixed solvent (water/ethanol) as the precipitation medium, the Cu-Ni alloy rods can be finally fabricated with high purity and crystallinity.

Radiation- and Photo-Induced Oxidation Pathways of Methionine in Model Peptide Backbone under Anoxic Conditions.

Within the reactive oxygen species (ROS) generated by cellular metabolisms, hydroxyl radicals (HO•) play an important role, being the most aggressive towards biomolecules. The reactions of HO• with methionine residues (Met) in peptides and proteins have been intensively studied, but some fundamental aspects remain unsolved. In the present study we examined the biomimetic model made of Ac-Met-OMe, as the simplest model peptide backbone, and of HO• generated by ionizing radiation in aqueous solutions under anoxic conditions. We performed the identification and quantification of transient species by pulse radiolysis and of final products by LC-MS and high-resolution MS/MS after γ-radiolysis. By parallel photochemical experiments, using 3-carboxybenzophenone (CB) triplet with the model peptide, we compared the outcomes in terms of short-lived intermediates and stable product identification. The result is a detailed mechanistic scheme of Met oxidation by HO•, and by CB triplets allowed for assigning transient species to the pathways of products formation.

Effects of the Incorporation of Distinct Cations in Titanate Nanotubes on the Catalytic Activity in NOx Conversion.

Effects of the incorporation of Cr, Ni, Co, Ag, Al, Ni and Pt cations in titanate nanotubes (NTs) were examined on the NOx conversion. The structural and morphological characterizations evidenced that the ion-exchange reaction of Cr, Co, Ni and Al ions with the NTs produced catalysts with metals included in the interlayer regions of the trititanate NTs whereas an assembly of Ag and Pt nanoparticles were either on the nanotubes surface or inner diameters through an impregnation process. Understanding the role of the different metal cations intercalated or supported on the nanotubes, the optimal selective catalytic reduction of NOx by CO reaction (SCR) conditions was investigated by carrying out variations in the reaction temperature, SO2 and H2O poisoning and long-term stability runs. Pt nanoparticles on the NTs exhibited superior activity compared to the Cr, Co and Al intercalated in the nanotubes and even to the Ag and Ni counterparts. Resistance against SO2 poisoning was low on NiNT due to the trititanate phase transformation into TiO2 and also to sulfur deposits on Ni sites. However, the interaction between Pt2+ from PtOx and Ti4+ in the NTs favored the adsorption of both NOx and CO enhancing the catalytic performance.

Polar polymorphism: β-Ca2[B5O8(OH)]2[B(OH)3]·H2O—synthesis, structure and nonlinear optical property

The hydrothermal reaction of H3BO3, CaCO3 and H2O led to a new polar polymorphs borate, β-Ca2[B5O8(OH)]2[B(OH)3]·H2O (β-CBO). It represents the first example of alkaline-earth metal borate with the polymorph being polar one under mild hydrothermal reaction. Compared with compound α-CBO (monoclinic system) which we have synthesized before, β-CBO crystallizes in the lower triclinic system with polar space group P1. The arrangement of β-CBO is –AAAA– sequence, while α-CBO is –ABAB– sequence. Further, β-CBO is type-I phase matchable with second-harmonic generation (SHG) responses of ~1.8 times of KH2PO4 (KDP), which is larger than α-CBO (~1.3 times of KDP). The dipole moments calculations show that the larger dipole moments make β-CBO exhibit a relatively larger SHG response.

Theoretical Study of an almost Barrier-Free Water Dissociation on a Platinum (111) Surface Alloyed with Ruthenium and Molybdenum.

A theoretical study based on density functional theory for H2O dissociation on the metal surface of Pt(111) alloyed simultaneously with Ru and Mo was performed. The determination of the minimum energy path using the climbing image nudged elastic band (CI-NEB) method shows that the dissociation reaction of H2O with this catalyst requires almost no energy cost. This dissociation reaction is not only kinetically favored but also almost thermodynamically neutral and somewhat exothermic. The electronic structure analysis showed that much more charge was released in Mo and was used to bind the adsorbed hydroxyl (OHad). Further analyses of the density of states (DOS) showed that the large number of orbitals that overlap when OH binds to Mo are responsible for the stabilization of the OH-surface bond. The stability of the OHad fragment on the surface is believed to be a descriptor for the dissociation of H2O with an almost spontaneous process.