Single Oxygen Molecule Research Articles

Four Generations of Volcano Plots for the Oxygen Evolution Reaction: Beyond Proton-Coupled Electron Transfer Steps?

ConspectusDue to its importance for electrolyzers or metal-air batteries for energy conversion or storage, there is huge interest in the development of high-performance materials for the oxygen evolution reaction (OER). Theoretical investigations have aided the search for active material motifs through the construction of volcano plots for the kinetically sluggish OER, which involves the transfer of four proton-electron pairs to form a single oxygen molecule. The theory-driven volcano approach has gained unprecedented popularity in the catalysis and energy communities, largely due to its simplicity, as adsorption free energies can be used to approximate the electrocatalytic activity by heuristic descriptors.In the last two decades, the binding-energy-based volcano method has witnessed a renaissance with special concepts being developed to incorporate missing factors into the analysis. To this end, this Account summarizes and discusses the different generations of volcano plots for the example of the OER. While first-generation methods relied on the assessment of the thermodynamic information for the OER reaction intermediates by means of scaling relations, the second and third generations developed strategies to include overpotential and kinetic effects into the analysis of activity trends. Finally, the fourth generation of volcano approaches allowed the incorporation of various mechanistic pathways into the volcano methodology, thus paving the path toward data- and mechanistic-driven volcano plots in electrocatalysis.Although the concept of volcano plots has been significantly expanded in recent years, further research activities are discussed by challenging one of the main paradigms of the volcano concept. To date, the evaluation of activity trends relies on the assumption of proton-coupled electron transfer steps (CPET), even though there is experimental evidence of sequential proton-electron transfer (SPET) steps. While the computational assessment of SPET for solid-state electrodes is ambitious, it is strongly suggested to comprehend their importance in energy conversion and storage processes, including the OER. This can be achieved by knowledge transfer from homogeneous to heterogeneous electrocatalysis and by focusing on the material class of single-atom catalysts in which the active center is well defined. The derived concept of how to analyze the importance of SPET for mechanistic pathways in the OER over solid-state electrodes could further shape our understanding of the proton-electron transfer steps at electrified solid/liquid interfaces, which is crucial for further progress toward sustainable energy and climate neutrality.

Ultrafast preparation and detection of entangled atoms.

Atoms can form a molecule by sharing their electrons in binding orbitals. These electrons are entangled. Is there a way to break a molecular bond and obtain atoms in their ground state that are spatially separated and still entangled? Here, we show that it is possible to prepare these spatially separated, entangled atoms on femtosecond time scales from single oxygen molecules. The two neutral atoms are entangled in the magnetic quantum number of their valence electrons. In a time-delayed probe step, we use nonadiabatic tunneling, which is a magnetic quantum number-sensitive ionization mechanism. We find a fingerprint of entanglement in the measured ionization probability as a function of the angle between the light's quantization axis and the molecular axis. This establishes a platform for further experiments that harness the time resolution of strong-field experiments to investigate spatially separated, entangled atoms on femtosecond time scales.

More of the same? Voxelotor spawns a successor, but on what success does it build?

More of the same? Voxelotor spawns a successor, but on what success does it build?

Investigation of the hexagonal boron nitride (h-BN) electronic and structural parameters and its dependency on the known semi-local functionals

Known as the next wonder material after graphene, hexagonal form of Boron-Nitride (hBN) attracts a lot of interest due to its capabilities to be utilized in wide range of applications. Here we investigate bilayer structure of hBN using density functional theory (DFT) techniques. In pristine case, we observed that the SCAN functional gives a significantly better estimation of inter-layer distance compared to the PBE functional. Furthermore, we also modelled the hBN structure with a single oxygen molecule sandwiched in between of B-N layer, and conclude that the most probable sites for oxygen molecule to be trapped is at the exact center of the bilayer hBN structure.

Molecular-resolution micro-resonant biosensor with adjustable natural frequency

Modern sensors are becoming increasingly small in size while their sensitivity requirements remain relatively strict, to the point that the processing technology and test technology are highly difficult and costly. This paper proposes a micro-resonant biosensor with adjustable natural frequency. A positive feedback signal with a phase difference of 180 degrees is used to reduce the equivalent mass of the resonator, yielding an ultrahigh resonant frequency. The biosensor is formed by a coating bovine blood solution on the surface of the resonator of a cantilever sensor. The instantaneous frequency equation of the biosensor is established using a coupling dynamic calculation. The changes in instantaneous frequency during hemoglobin oxygen absorption and deoxygenation, are then measured. The proposed millimeter micro-resonant biosensor system measures the molecular weight of a single oxygen molecule quality at 5.7619×10−23 g, only deviating by 8.306 % from the theoretical value. Finally, the potential of the micron scale sensor is deeply taped.

Ultrahigh sensitive and selective triethylamine sensor based on h-BN modified MoO3 nanowires

In this work, a novel structure of 1D MoO3 nanowires wrapped by 2D hexagonal boron nitride (h-BN) was synthesized via a simple solvothermal method with subsequent annealing process for triethylamine (TEA) detection. The samples were characterized by XPS, SEM, HRTEM and N2 adsorption-desorption. Gas sensing performance test results illuminate that the typical 2 wt% h-BN/MoO3 sensor possesses an ultrahigh response (8616) toward 500 ppm TEA. The promoted sensing performance of TEA may be caused by the forming of heterojunction between h-BN and MoO3, the increased specific surface area of h-BN modification, providing a highly active sites for the adsorption of TEA gas, which greatly enhance the response of the sensor. The adsorption energy of a single oxygen molecule on MoO3 (010) surface was calculated by DFT, indicating the most stable site is the terminal oxygen position (Top O-1), with an adsorption energy of −2.075 eV. This work provides an inspiration to design highly efficient TEA gas sensor on basis of h-BN/MoO3 nanocomposites.

Effects of oxygen adsorption on spin transport properties of single anthracene molecular devices

With the miniaturization of molecular devices, high-performance nano devices can be fabricated by controlling the spin states of electrons. Because of their advantages such as low energy consumption, easy integration and long decoherence time, more and more attention has been paid to them. So far, the spin filtration efficiency of molecular device with graphene electrode is not very stable, which will decrease with the increase of voltage, and thus affecting its applications. Therefore, how to enhance the spin filtration efficiency of molecular device with graphene electrode becomes a scientific research problem. Using the first principle calculations based on density functional theory combined with non-equilibrium Green’s function, the physical mechanism of regulating the spin polarization transport properties of single anthracene molecule device with graphene nanoribon as electrode is investigated by molecular oxygen adsorption. In order to explore the effect of the change of the connection mode between single anthracene molecule and zigzag graphene nanoribbon electrode on the spin transport properties of the device, we establish two models. The first model is the model M1, which is the single anthracene molecule longitudinal connection, and the second model is the model M2, which is the single anthracene molecule lateral connection. The adsorption model of single oxygen molecule is denoted by M1O and M2O respectively. The results show that when none of oxygen molecules is adsorbed, the spin filtering effect of single anthracene molecule connecting graphene nanoribbons laterally (M2) is better than that of single anthracene molecule connecting graphene nanoribbons longitudinally (M1). After oxygen molecules are adsorbed on single anthracene molecule, the enhanced localized degree of transport eigenstate will make the spin current of the two kinds of devices decrease by nearly two orders of magnitude. However, molecular oxygen adsorption significantly improves the spin filtering efficiency of the device and enhances the application performance of the device. The maximal spin filtering efficiency of single anthracene molecule connecting graphene nanoribbons longitudinal (M1O) can be increased from 72% to 80%. More importantly, the device with single anthracene molecule connecting graphene nanoribbons laterally (M2) maintains nearly 100% spin filtering efficiency in a bias range from –0.5 V to +0.5 V. These results provide more theoretical guidance for practically fabricating spin molecular devices and regulating their spin transport properties.

Orientation-specific switching of inelastic electron tunneling in an oxygen-pyridine complex adsorbed onto an Ag(110) surface.

Here, we report the development of a molecular rotary switch (a "stator-rotor" consisting of a single oxygen molecule as a stator and a single pyridine molecule as a rotor) on a silver surface. The pyridine molecule was bonded to the oxygen molecule and was found to rotate to enable "ON" or "OFF" vibrational conductance through the oxygen molecule. Four stable sites around the oxygen molecule were observed, and vibration conductance turned on and off depending on the site at which the pyridine molecule bonded. The spatially resolved mapping of the vibrational change revealed two locations of maximal vibration intensity, separated by ∼3 Å. These positions acted as two conducting channels. The two distinct vibrational energy levels were associated with the switching process. Adsorption-induced electron transfer between the silver layers and the molecules enhanced the local interactions between the molecules. The two vibration modes were excited by resonant tunneling despite substantial interactions between the molecules, which resulted in a decrease in tunneling conductance. An independent pathway exists for the vibrational excitation process by tunneling electrons and intermolecular interactions.

Local Mass Transfer Phenomena and Chemical Selectivity of Gas‐Liquid Reactions in Capillaries

W. Krieger*, J. Lamsfuß, W. Zhang, N. Kockmann, Chem. Eng. Technol. 2017, 40 (11), 2134–2143. DOI: https://doi.org/10.1002/ceat.201700420 The article reported on a color reaction for determining selectivity in gas-liquid reactions. The stoichiometric values were taken from literature [8] and integrated into the calculations and discussion. Current own stoichiometry and mass balance measurements of the oxidation of leuco-indigo carmine lead to corrected values of a single oxygen molecule only needed for each oxidizing step, shown below. Particularly, the mass transfer coefficients must be corrected towards higher values. The authors apologize for the error and want to correct the publication as follows: Fig. 1 should be as shown below. Leuco-indigo carmine occurs in its deprotonated state due to the alkaline solution. Fig. 2 should be as shown below according to the corrected stoichiometry. The proposed mechanism is supported by [17]. Figs. 10 and 11 should be as shown below due to the corrected stoichiometry. On page 2141, right column, line 7 should read “The attained kLa values range from 7.08 to 16.52 × 10−2 s−1 and are comparable to data from the literature for microchannels and capillaries [22, 23].” On page 2142, left column, lines 22–24 should read “Mass transfer investigations led to kLa values for straight and coiled capillaries in the order of 5–20 × 10−2 s−1, which are in reasonable agreement with data from literature.”

Transition metal doped puckered arsenene: Magnetic properties and potential as a catalyst

Puckered arsenene is a new two-dimensional group V elemental material which has sparked much research interest owing to its fascinating properties and potential applications in various fields. To further widen its application, we studied arsenene doped with 10 different transition metals (TMs) by using first-principles calculations, focusing on the structural, electronic, and magnetic properties of TM-doped arsenene. Our calculation results show that all the substitutional systems have large binding energy, suggesting the formation of chemical bonds and consequently robust structural stability. The substitution of Ti, V, Cr, Mn, Fe and Ni atoms for As atoms induces a magnetic moment of 1, 2, 3, 4, 3, and 1 μB in arsenene, respectively. Moreover, the V-, Mn- and Fe-doped systems exhibit half-metallic properties, while the Ti-, Cr-, and Ni-doped systems exhibit magnetic semiconductor properties. Adsorption of a single oxygen molecule on TM-doped arsenene was also investigated to determine whether O2 can widen the application of substitutional arsenene systems for spintronic devices. The adsorption of a single oxygen molecule turns the Ti-, V-, Cr-, Mn-, Fe-, Co-, Ni-, and Pt-arsenene systems to magnetic metals which can be used as spin sources and drains in spintronic circuits. Interestingly, all the substitutional systems show good catalytic activity for CO oxidation since they can elongate the OO bond. In particular, after O2 is adsorbed on the Sc-arsenene system, the O2 molecule is almost decomposed, which provides much information on the requirements for a suitable CO oxidization catalyst with high activity and low cost. Our results are expected to lead to new opportunities for arsenene in spintronics and catalysts.

Experimental results on the dissociation of molecular iodine in the presence of singlet oxygen molecules

The experimental results on the dissociation of iodine molecules in the presence of single oxygen molecules under a wide-range variation of the oxygen – iodine composition are presented. The rate constants are determined as for the reaction (reaction 1), for the reaction and for the reaction . The analysis of the experimental results shows that for different compositions of the active medium of the oxygen – iodine laser the iodine dissociation occurs via the chain of reactions , 4 and in the cascade process . For typical active medium compositions of the supersonic chemical oxygen – iodine laser, the contributions of each of the mechanisms to the dissociation are comparable. The experiments carried out did not reveal any contribution from the vibrationally excited oxygen molecules to the iodine dissociation. Thus, the performed experiments and the conclusions drawn from them completely confirm the mechanism of iodine dissociation, proposed earlier.

Kinetic modeling and determination role of sono/photo nanocatalyst-generated radical species on degradation of hydroquinone in aqueous solution.

Experimental findings of sonophotocatalytic process were used in degradation of hydroquinone to assess kinetic modeling and determine the effect of various active radical species. First, the effects of three photocatalytic, sonocatalytic, and sonophotocatalytic processes were studied for hydroquinone removal to determine kinetic constants and calculate the activation energy of reactions, and then the selected process was evaluated to determine active radical species. The reactor was composed of two parts, one included ultrasonic probe (sonocatalytic part) with powers 22, 80, and 176W and the second part was the location of UV lamp (photocatalytic part) with tubular flow and power 15W. After three systems were examined and the efficient system was selected, the role of different active species such as hydroxyl radical (OH(·)), superoxide radical (O2 (·-)), hole (h(+)), electrons (e (-)), and single oxygen molecule ((1)O2) and contribution of each of them were determined in hydroquinone degradation. According to tests, the results of this study showed that sonophotocatalytic integrated method as selected system among three systems studied followed the first-order equation for hydroquinone degradation and active hydroxyl species with 45% and electron and hole with 15 and 10%, respectively, had the highest and lowest contributions to conversion of hydroquinone. The findings showed that dissolved oxygen increases the capability of active radical formation so that 28.2% of hydroquinone removal was increased under aeration compared to without aeration. Also, removal efficiency decreased 62% with N2 injection due to the withdrawal of oxygen from the sample. By adding 25Mm of sodium azide (NaN3) to stock solution, 46.5% reduction was developed because single oxygen ((1)O2) played the role of an active species. The advantages of integrated sonocatalytic and photocatalytic method are the generation of active radical species with more variety and ultimately the formation of higher amounts of powerful hydroxyl radical that increases degradation rates of refractory compounds and low-risk internal and final products. It has an appropriate performance in the degradation of refractory compounds by optimizing effective operational factors.

Electrocatalysis of Oxygen Reduction Reaction By Transition Metal Corroles

Introduction Oxygen reduction plays a crucial role in numerous biological processes and is also a half-cell reaction in electrochemical power sources, such as polymer electrolyte fuel cells (PEFCs) or metal/air batteries. In the quest to replace expensive and scarce platinum used as oxygen reduction catalyst in PEFCs,1various alternative electrocatalysts have been explored, including transition metal porphyrins, which frequently participate in biological cycles, which involve oxygen reduction.Corroles are a class of corrin based macrocyclic compounds. In spite of similarities between transition metal corroles and porphyrins, there are also notable differences between these two classes of complexes. The differences in some of their properties result from different charges and symmetries of the ligands (Fig. 1a and 1b), which directly affect the electronic environment of the metal and thus its potential activity in catalytic processes. Fig. 1. Corrin ring (a), porphine ring (b) and [5,15-C6F5)-10-(p-OMePh)Corrole]M (c)Elucidation of the catalytic activity of [5,15-C6F5)-10-(p-OMePh)Corrole]M (Fig. 1c), where M=Cu, Fe, Co, in electrochemical reduction of oxygen was a subject of the present study. Experimental The corroles were synthesized using the method described previously.2Their electrochemical/catalytic properties in non-aqueous solvents were examined using standard cyclic voltammetry on stationary electrodes. Electrocatalysis of oxygen reduction in aqueous sulfuric acid solutions by the corroles adsorbed on a high surface area carbon (XC 72) was studied using a standard rotating ring disk electrode (RRDE) technique. Results Figure 2 presents RRDE voltammograms of oxygen in 0.5 M H2SO4 obtained for comparable loadings of monomolecular copper and cobalt corroles and dimeric, μ-oxo bridged iron corrole. As seen in Fig. 2, the overall catalyst activity increases in the order Cu < Fe(μ-oxo) < Co. However, none of the catalysts exhibited a high selectivity for the desired four electron reduction of oxygen to water. The average number of electrons transferred to a single oxygen molecule was found to be 2.0 (only H2O2 generated) for the Co corrole and 2.8 (60% of O2 reduced to H2O2) for both Cu and Fe corroles. Fig. 2. RRDE voltammograms for oxygen reduction catalyzed by copper (blue) and cobalt (purple) corroles and μ-oxo bridged iron corrole (green).A strong interaction was detected between oxygen dissolved in solution and μ-oxo iron corrole in the unreduced form. The free energy of the adduct formation was similar to that previously determined for pyrolyzed Fe-polyaniline oxygen reduction catalysts.3However, the kinetics of the reaction was significantly faster than that for the pyrolyzed catalyst. Acknowledgements Financial assistance from the University of California and the Haas Scholar Progam (B.J.M) is gratefully acknowledged. References 1) J.-P. Dodelet, Oxygen Reduction in PEM Fuel Cell Conditions: Heat-Treated Non-Precious Metal-N4Macrocycles and Beyond. In N4-Macrocyclic Metal Complexes; J. H. Zagal, F. Bedioui, J.-P. Dodelet, Eds.; Springer: New York, 2006; pp 83-1472) D. T. Gryko, K. J. Jadach, J. Org. Chem., 66(12), 4267-4275 (2001)3) J. Chlistunoff, J. Phys. Chem. C, 115, 6496-6507 (2011)

Photosynthesis: Light and Life

Complex life on Earth requires oxygen as the terminal electron acceptor in the respiratory chain. However, the lifetime of a single oxygen molecule in the atmosphere is only 4500 years. Oxygen is continually being replenished by the action of photosynthetic organisms, using the only substantial energy input to the Earth, sunlight. How this light energy is harvested and used is of fundamental biological importance, and may be of crucial importance in developing sustainable energy technologies.

A Molecular Dynamics Simulation Study on the Initial Stage of Si(001) Oxidation Under Biaxial Strain

We have studied the very early stage of the room temperature oxidation of the externally-strained Si(001) surface using molecular dynamics simulation. It was found that the different treatment history of the sample under the same strain resulted in the difference in the number density of dimer. The as-prepared samples of different treatment history with 12.15% strain were used to investigate the initial oxidation behavior of Si(001). 500 times of independent deposition of single oxygen molecule onto the random position of clean Si(001) surface was simulated. Oxidation behavior was statistically analyzed for various dimer density of the surface which is dependent on strain-treatment history. Oxygen uptake and penetration depth profile showed an important role of dimers on the surface oxidation behavior.

Vapour phase oxidation of cyclohexane over CeAlPO-5 molecular sieves

Single sited CeAlPO-5 molecular sieves exhibit activity, selectivity and recyclability. In this study crystalline CeAlPO-5(Al/Ce = 25, 50, 75, 100 and 125) were synthesized hydrothermally in fluoride medium for the selective oxidation of cyclohexane. The framework incorporation of cerium in AlPO-5 and absence of separate ceria phase were verified from XRD analysis. Diffuse reflectance spectral analysis also confirmed the absence of free ceria phase in CeAlPO-5. Electron spin resonance study revealed sorption of molecular oxygen in CeAlPO-5(25). Their catalytic activity was tested in the vapour phase oxidation of cyclohexane in air. Cyclohexanone was obtained as the main product (>90% selectivity). Oxidation of cyclohexane to cyclohexanol and then to cyclohexanone was postulated to occur on the same single oxygen molecule via radical mechanism. The stability, activity and selectivity of the catalysts were verified from time on stream study. It is concluded that CeAlPO-5 may be a convenient catalyst for the selective oxidation of cyclohexane.

A First Principles Study on the Dissociation and Rotation Processes of a Single O2 Molecule on the Pt(111) Surface

Through density functional theory calculations, a detailed description on the dissociation and rotation processes of a single oxygen molecule adsorbed on the Pt(111) surface has been provided. Both dissociation and rotation reaction pathways have been identified, and some interesting phenomena related to the scanning tunneling microscopy experiments are finally explained. It is found that the prior occupation of oxygen atom on the metastable hcp-hollow site after O2 dissociation is originated from the particular structure of the intermediate state, and the low energy barrier of the O2 rotation can be attributed to an effective pathway. The experimentally observed noninteger power-law dependence of the rotation rate as a function of the current has been accurately determined by a newly developed statistical model for the inelastic electron tunneling. By considering the randomness of multielectron inelastic tunneling processes, it is found that the noninteger exponent comes from a statistical contribution of various n-electron events.

Identifying atomic geometry and electronic structure of (2×3)-Sr/Si(100) surface and its initial oxidation

We present a joint experimental and theoretical study on the geometric and electronic states and the initial oxidation of the (2x3)-Sr/Si(100) surface. With scanning tunneling microscopy/scanning tunneling spectroscopy (STM/STS) measurements combined with ab initio calculations, the atomic geometry and the electronic states of the (2x3)-Sr/Si(100) surface are identified. The dimerization of the Si atoms in the single atom row based on a (1x3) Si substrate model plays a critical role in stabilization of the surface structure and in determining the electronic properties. At the very initial oxidation of the surface, four features corresponding to the primary adsorption and oxidation sites are determined. Three of them are corresponding to the most favored oxidation sites with single oxygen molecules, whose local density of states gives semiconducting behavior. One is corresponding to the oxidation site with two oxygen molecules, whose local density of states gives metallic behavior. These features all exhibit dark spots with different shapes in the occupied state images but display either dark spots or bright protrusions depending on the different oxidation sites in the empty state images. Compared with the theoretical calculations, the plausible adsorption and oxidation models are proposed.

Melting-Point Depression by Insoluble Impurities: A Finite Size Effect

Melting-point depression by soluble impurities is an entropy-driven phenomenon. Studying partially oxidized free sodium nanoparticles, we found an additional mechanism, which is caused by insoluble impurities. Oxidization of sodium clusters with 135-192 atoms by a single oxygen molecule causes a melting-point depression of 17+/-6 K; additional oxygen amplifies the effect. This is in contrast to the behavior of bulk sodium, where the melting point does not change upon partial oxidization. First-principles density functional theory calculations reveal the interaction between the pure and the oxidized part of the cluster to be responsible for the effect. There is more structural freedom in a liquid cluster to optimize the interface between the two parts. This stabilizes the liquid phase and causes the observed, cluster-specific melting-point depression.

Structural and Biochemical Basis for the Binding Selectivity of Peroxisome Proliferator-activated Receptor γ to PGC-1α

The functional interaction between the peroxisome proliferator-activated receptor gamma (PPARgamma) and its coactivator PGC-1alpha is crucial for the normal physiology of PPARgamma and its pharmacological response to antidiabetic treatment with rosiglitazone. Here we report the crystal structure of the PPARgamma ligand-binding domain bound to rosiglitazone and to a large PGC-1alpha fragment that contains two LXXLL-related motifs. The structure reveals critical contacts mediated through the first LXXLL motif of PGC-1alpha and the PPARgamma coactivator binding site. Through a combination of biochemical and structural studies, we demonstrate that the first LXXLL motif is the most potent among all nuclear receptor coactivator motifs tested, and only this motif of the two LXXLL-related motifs in PGC-1alpha is capable of binding to PPARgamma. Our studies reveal that the strong interaction of PGC-1alpha and PPARgamma is mediated through both hydrophobic and specific polar interactions. Mutations within the context of the full-length PGC-1alpha indicate that the first PGC-1alpha motif is necessary and sufficient for PGC-1alpha to coactivate PPARgamma in the presence or absence of rosiglitazone. These results provide a molecular basis for specific recruitment and functional interplay between PPARgamma and PGC-1alpha in glucose homeostasis and adipocyte differentiation.