H2 Desorption Research Articles

Improved activity and stability for chlorobenzene oxidation over ternary Cu-Mn-O-Ce solid solution supported on cordierite.

A series of CuMnOx/CeO2/cordierite and CuMnCeOx/cordierite catalysts prepared by a complex method with citric acid were investigated for the performance of chlorobenzene (CB) oxidation. The effects of the molar ratio of Mn/Cu, transition metal oxide loading, calcination temperature and time were investigated as the main investigation factor for the performance. Meanwhile, XRD, SEM, BET, H2-TPR, O2-TPD and XPS were conducted to characterize the physicochemical properties of these catalysts. The results demonstrated that CuMnOx/CeO2/cordierite catalysts prepared by step-by-step synthesis with the Cu/Mn molar ratio of 5:2 exhibited a high activity (T90 = 350°C), owing to the incorporation of CuO and MnOx for forming CuMn2O4 spinel oxide supported on CeO2 surface. More importantly, CuMnCeOx/cordierite catalysts prepared by one-step exhibited the highest oxidation activity (T90 < 300°C) attributed to the low H2 reduction temperature and desorption energy of surface oxygen, and the formed Cu-Mn-O-Ce solid solution and CeO2 promoted the high dispersion of CuMnOx in the supported catalysts. In addition, the possible oxidation mechanism was described to demonstrate the by-products generation and oxygen transfer of CuMnCeOx catalysts.

The rare earth doped Mg2Ni (0 1 0) surface enhances hydrogen storage

Rare earth doping has been proved to be an effective method to improve hydrogen storage properties of Mg-based alloys. In this work, the effect of rare earth (Y, Ce, La, Sc) doping on the thermal stability, electronic property and hydrogen adsorption/desorption behavior of Mg2Ni (010) surface are systematically investigated by first principles calculation. The results show that rare earth doping in Mg2Ni (010) surface are thermodynamic feasible. The calculated electronic structures shown that rare earth atoms weaken the binding strength between H and Mg2Ni (010) substrate, thus reduce the hydrogen diffusion and desorption energies barriers, and improve the hydrogen storage properties of Mg2Ni. Among the four rare earth elements, Ce shows the best potential. Notably, the substitution doping of Ce to Mg atom significantly reduces the H diffusion barrier by 0.32 eV and H2 desorption barrier by 1.0 eV. This discovery provides a direction for the preparation of rare earth doped Mg2Ni hydrogen storage materials.

Controlling Selectivity in Plasmonic Catalysis: Switching Reaction Pathway from Hydrogenation to Homocoupling Under Visible-Light Irradiation.

Plasmonic catalysis enables the use of light to accelerate molecular transformations. Its application to the control reaction selectivity is highly attractive but remains challenging. Here, we have found that the plasmonic properties in AgPd nanoparticles allowed different reaction pathways for tunable product formation under visible-light irradiation. By employing the hydrogenation of phenylacetylene as a model transformation, we demonstrate that visible-light irradiation can be employed to steer the reaction pathway from hydrogenation to homocoupling. Our data showed that the decrease in the concentration of H species at the surface due to plasmon-enhanced H2 desorption led to the control in selectivity. These results provide important insights into the understanding of reaction selectivity with light, paving the way for the application of plasmonic catalysis to the synthesis of 1,3-diynes, and bringing the vision of light-driven transformations with target selectivity one step closer to reality.

Controlling Selectivity in Plasmonic Catalysis: Switching Reaction Pathway from Hydrogenation to Homocoupling Under Visible‐Light Irradiation

AbstractPlasmonic catalysis enables the use of light to accelerate molecular transformations. Its application to the control reaction selectivity is highly attractive but remains challenging. Here, we have found that the plasmonic properties in AgPd nanoparticles allowed different reaction pathways for tunable product formation under visible‐light irradiation. By employing the hydrogenation of phenylacetylene as a model transformation, we demonstrate that visible‐light irradiation can be employed to steer the reaction pathway from hydrogenation to homocoupling. Our data showed that the decrease in the concentration of H species at the surface due to plasmon‐enhanced H2 desorption led to the control in selectivity. These results provide important insights into the understanding of reaction selectivity with light, paving the way for the application of plasmonic catalysis to the synthesis of 1,3‐diynes, and bringing the vision of light‐driven transformations with target selectivity one step closer to reality.

Hydrogen Atom Adsorption-Induced Spin Reversal and Vacancies Boosting Hydrogen Evolution Reaction in Defective H-VS2 Monolayers

Spin reversal induced by adsorbates will cause intersite communication between the active and adjacent sites, which modulates the exchange coupling strength and spin alignment direction of adjacent atoms. Here, spin reversal induced by H adsorption and hydrogen evolution reaction (HER) performance of defective H-VS2 are studied by density-functional theory. The spin of V/S atoms around double S vacancies on different atomic layers (V2S) exhibits continuous reversals with H adsorption, which reverses once for S atoms around single V vacancy (VV). Moreover, the adsorption energies of the second H atom decreased in V2S- and VV-modified H-VS2 systems. Additionally, V2S and VV can activate the inert basal plane of H-VS2, and the increased antibonding filling and p-band center in H-VS2 with VV will weaken the interaction between S–H atoms and promote the desorption of H2, which causes lower Gibbs free energy in H-VS2 with VV than V2S and the pure H-VS2 monolayer.

Synthesis of Ni-phyllosilicate assisted by fluoroboric acid for CO2 methanation

How to efficiently prepare nickel phyllosilicate using the calcined biomass-based silica as the sacrificial template under the mild condition is a challenge. In this work, NH4HF2, H2SiF6 and HBF4 were used as the assistor to facilitate the synthesis of Ni-phyllosilicate, which could be successfully synthesized under the mild condition of 120 °C for 12 h. Compared with NH4HF2 and H2SiF6, HBF4 was the best fluorine-containing assistor. The HBF4-assisted Ni phyllosilicate catalyst (Ni-Ps/B) exhibited the high CO2 conversion of 80.0% and CH4 selectivity of 98.3% at 450 °C due to its small particle size of 3.8 nm, high Ni content of 21.65 wt% as well as enhanced H2 and CO2 desorption capacity. The characterization results showed that HBF4 converted to B2O3 after the hydrothermal reaction and thermal treatments, which could not only provide the physical barrier for Ni species during reduction process, but also be a promoter for Ni-Ps/B for CO2 methanation. In all, HBF4 was a competitive fluorine-containing assistor for the highly efficient synthesis of Ni-phyllosilicate catalysts.

Hydrogen induced structural phase transformation in ScNiSn-based intermetallic hydride characterized by experimental and computational studies

Understanding an interrelation between the structure, chemical composition and hydrogenation properties of intermetallic hydrides is crucial for the improvement of their hydrogen storage performance. Ability to form the hydrides and to tune the thermodynamics and kinetics of their interaction with hydrogen is related to their chemical composition. Some features of the metal–hydrogen interactions remain however poorly studied, including chemistry of Sc-containing hydrides. ZrNiAl-type ScNiSn-based intermetallic hydride has been probed in the present work using a broad range of experimental techniques including Synchrotron and Neutron Powder Diffraction, 119Sn Möessbauer Spectroscopy, hydrogenation at pressures reaching several kbar H2 and hydrogen Thermal Desorption Spectroscopy studies. Computational DFT calculations have been furthermore performed. This allowed to establish the mechanism of the phase-structural transformation and electronic structure changes causing a unique contraction of the metal lattice of intermetallic alloy and the formation of the ...H-Ni-H-Ni… chains in the structure with H atoms carrying a partial negative charge. Such hydrogen absorption accompanied by a formation of a covalent Ni-H bonding and causing an unusual behavior contracts to the conventionally observed bonding mechanism of hydrogen in metals as based on the metallic bonding frequently accompanied by a jumping diffusion movement of the inserted H atoms – in contrast to the directional Metal-Hydrogen bonding observed in the present work. At high applied pressures ScNiSnH0.83 orthorhombic TiNiSi type hydride is formed with H atoms filling Sc3Ni tetrahedra. Finally, this study shows that scandium closely resembles the behavior of the heavy rare earth metal holmium.

Revealing the interfacial phenomenon of metal-hydride formation and spillover effect on C48H16 sheet by platinum metal catalyst (Pt (n=1-4)) for hydrogen storage enhancement

Hydrogen is a worldwide green energy carrier, however due its low storage capacity, it has yet to be widely used as an energy carrier. Therefore, the quantum chemical method is being employed in this investigation for better understand the hydrogen storage behaviour on Pt (n = 1-4) cluster decorated C48H16 sheet. The Pt(n = 1-4) clusters are strongly bonded on the surface of C48H16 sheet with binding energies of −3.06, −4.56, −3.37, and −4.03 eV respectively, while the charge transfer from Pt(n = 1-4) to C48H16 leaves an empty orbital in Pt atom, which will be crucial for H2 adsorption. Initially, the molecular hydrogen is adsorbed on Pt(n = 1-4) decorated C48H16 sheet through the Kubas interaction with adsorption energies of −0.85, −0.66, −0.72, and −0.57 eV respectively, while H–H bond is elongated due to the transfer of electron from σ (HH) orbital to unfilled d orbital of the Pt atom, resulting in a Kubas metal-dihydrogen complexes. Furthermore, the dissociative hydrogen atoms adsorbed on Pt(n = 1-4) decorated C48H16 sheet have adsorption energies of −1.14 eV, −1.02 eV, −0.95 eV, and −1.08 eV, which are greater than the molecular hydrogen adsorption on Pt(n = 1-4) cluster supported C48H16 sheet with lower activation energy of 0.007, 0.109, 0.046, and 0.081 eV respectively. To enhance the dissociative hydrogen adsorption energy, positive and negative external electric fields are applied in the charge transfer direction. Increasing the positive electric field makes H–H bond elongation and good adsorption, whereas increasing the negative electric field results H–H bond contraction and poor adsorption. Thus, by applying a sufficient electric field, the H2 adsorption and desorption processes are can be easily tailored.

X-ray and Synchrotron FTIR Studies of Partially Decomposed Magnesium Borohydride

Magnesium borohydride (Mg(BH4)2) is an attractive compound for solid-state hydrogen storage due to its lucratively high hydrogen densities and theoretically low operational temperature. Hydrogen release from Mg(BH4)2 occurs through several steps. The reaction intermediates formed at these steps have been extensively studied for a decade. In this work, we apply spectroscopic methods that have rarely been used in such studies to provide alternative insights into the nature of the reaction intermediates. The commercially obtained sample was decomposed in argon flow during thermogravimetric analysis combined with differential scanning calorimetry (TGA-DSC) to differentiate between the H2-desorption reaction steps. The reaction products were analyzed by powder X-ray diffraction (PXRD), near edge soft X-ray absorption spectroscopy at boron K-edge (NEXAFS), and synchrotron infrared (IR) spectroscopy in mid- and far-IR ranges (SR-FTIR). Up to 12 wt% of H2 desorption was observed in the gravimetric measurements. PXRD showed no crystalline decomposition products when heated at 260–280 °C, the formation of MgH2 above 300 °C, and Mg above 320 °C. The qualitative analysis of the NEXAFS data showed the presence of boron in lower oxidation states than in (BH4)−. The NEXAFS data also indicated the presence of amorphous boron at and above 340 °C. This study provides additional insights into the decomposition reaction of Mg(BH4)2.

Insights of hydrogen adsorption and dissociation on Ni doped Mg4 clusters: A DFT study

Hydrogen adsorption and dissociation on Mg4 and NiMg3 clusters are studied using DFT method. Physisorption of hydrogen molecule on Mg4 is extremely weak, which however significantly strengthens on Ni doped Mg4 cluster. Following the physisorption mechanism, NiMg3 cluster can adsorb three H2 molecules at most and the cluster geometry plays an important role here. On the other hand, physisorption followed by chemisorption facilitates the growth of hydrogen adsorption process in both Mg4 and NiMg3 clusters. Further, dissociation and diffusion of H2 become more favourable on Ni doped Mg4 cluster resulting in a larger number of H2 adsorbed on NiMg3 compared to that on Mg4. NiMg3 is found to exhibit practically attainable H2 desorption energies lower than those for bare Mg4 clusters.

Construction of hierarchical and self-supported NiFe-Pt3Ir electrode for hydrogen production with industrial current density

Rational design and fabrication of electrocatalysts from the perspective of mass transfer and electronic structure is highly desirable for hydrogen evolution reaction (HER). Herein, a hierarchical and self-supported electrode comprising Cu nanowires, NiFe nanosheets, and Pt3Ir alloy nanoparticles (Cu NWs@NiFe-Pt3Ir) was in situ constructed and established as a highly active and robust electrocatalyst for HER with industrial current densities. Benefiting from the hierarchical structure, abundant active sites, and positive electronic interaction between NiFe and Pt3Ir, the Cu NWs@NiFe-Pt3Ir electrode shows extremely low overpotentials of 210 and 239 mV to reach industrial current densities of 500 and 1000 mA cm−2 in 1.0 M KOH solution, respectively. More importantly, Cu NWs@NiFe-Pt3Ir electrode shows robust durability with a slight increment of 8 mV for the required potential after consecutive tests for 7 days under 500 mA cm−2. As further revealed by electrochemical and theoretical studies, the reaction kinetics of NiFe is greatly promoted by coupling with Pt3Ir, and the d-band center energy level of Pt 5d orbital is lowered by Ir atom, which not only facilitates the electron consumption at the electrode/electrolyte interface but also optimizes the energies for H adsorption and H2 desorption. This work provides valuable insights into the construction of self-supported electrodes with extraordinary activity and durability for industrial applications.

Design of Bifunctional Nb/V Interfaces for Improving Reversible Hydrogen Storage Performance of MgH2

Solid-State Hydrogen Storage In article number 2200119, Xuebin Yu, Guanglin Xia, and co-workers realized uniform formation of Nb/V interfaces based on a molecular scale to promote H2 storage performance of MgH2. The onset H2 desorption temperature of MgH2 of 165 °C and the reversible hydrogenation of Mg at room temperature could be realized.

Hydrogen storage capacity and reversibility of Li-decorated B4CN3 monolayer revealed by first-principles calculations

This work explored the feasibility of Li decoration on the B4CN3 monolayer for hydrogen (H2) storage performance using first-principles calculations. The results of density functional theory (DFT) calculations showed that each Li atom decorated on the B4CN3 monolayer can physically adsorb four H2 molecules with an average adsorption energy of −0.23 eV/H2, and the corresponding theoretical gravimetric density could reach as high as 12.7 wt%. Moreover, the H2 desorption behaviors of Li-decorated B4CN3 monolayer at temperatures of 100, 200, 300 and 400 K were simulated via molecular dynamics (MD) methods. The results showed that the structure was stable within the prescribed temperature range, and a large amount of H2 could be released at 300 K, indicative of the reversibility of hydrogen storage. The above findings demonstrate that the Li-decorated B4CN3 monolayer can serve as a favorable candidate material for high-capacity reversible hydrogen storage application.

Metal Organic Framework-Derived ZnO@GC Nanoarchitecture as an Effective Hydrogen Gas Sensor with Improved Selectivity and Gas Response

Although they are not as favorable as other influential gas sensors, metal-oxide semiconductor-based chemiresistors ensure minimal surface reactivity, restricting their gas selectivity, gas response, and reaction kinetics, particularly when functioning at room temperature (RT). A hybrid design, which includes metal-oxide/carbon nanostructures and passivation with specific gas filtration layers, can address the concerns of surface reactivity. We present a novel hierarchical nanostructured zinc oxide (ZnO), decorated with graphitic carbon (GC) and synthesized via a wet-chemical strategy, which is then followed by the self-assembly of a zeolitic imidazolate framework (ZIF-8). Because of its large surface area, high porosity, and efficient inspection of other analyte (interfering) gases, the ZnO@GC can provide intensified surface reactivity at RT. In the present study, such a hybrid sensor confirmed extraordinary gas sensing properties, which was characterized by excellent H2 selectivity, fast response, rapid recovery kinetics, and high gas response (ΔR/R0 ∼ 124.6%@10 ppm), particularly in extremely humid environments. The results reveal that adsorption sites provided by the ZIF-8 template-based ZnO@GC frameworks facilitate the adsorption and desorption of H2.

Regulating d-orbital electronic character and HER free energy of VN electrocatalyst by anchoring single atom

Too strong or too weak orbital electron-coupling with active adsorbents basically results in unsatisfied free energies, and consequently limiting the HER kinetics and activity. Herein, Co-VN catalyst is fabricated to highlight that atomically implanted Co into VN can regulate its d orbital electronic character and corresponding free energy for further improving its alkaline HER performances. Experimental results and density functional theory calculations reveal that atomically implanted Co into VN could induce local charge redispersion to further downshift the d band center position of V-3d in Co-VN. The lowered d band center of the V-3d could not only decrease the d orbital electron-coupling between V site and O atom of OH intermediate to boost desorption of OH species and H2O dissociation kinetics, but also simultaneously balance the hydrogen adsorption free energy to facilitate the desorption of as-formed H2, both of which synergistically increase the Volmer and Heyrovsky kinetics and overall HER activity of Co-VN. Moreover, the structural stability of Co-VN after long-term HER is also investigated by transmission electron microscopy and X-ray photoelectron spectroscopy to uncover its activity-stability trade-off riddle. As a result, Co-VN catalyst expectantly displays a low overpotential of 59 mV at −10 mA cm−2, a small Tafel slope of 46.3 mV dec−1, and a favorable long-term stability. The proposed regulation strategy of orbital electronic structure and free energy could be extended to design other high-performance catalysts.

Single transition metal atom stabilized on double metal carbide MXenes for hydrogen evolution reaction: a density functional theory study

Double metal carbide MXenes have received considerable attention for use in renewable energy storage technologies in recent years. Here, density functional theory calculations were performed to investigate the hydrogen evolution reaction (HER) performances of double metal carbide MXenes (Cr2TiC2O2 and the Mo2TiC2O2 monolayer (ML) modified by a single transition metal (TM) atom (Co, Ni, Cu, Zn, Rh, Pd, Ag, Cd, Ir, Pt, Au, or Hg)). The thermodynamic stabilities of TM adatoms on pristine Cr2TiC2O2 and Mo2TiC2O2 MLs and defective Cr2TiC2O2 and Mo2TiC2O2 MLs with oxygen vacancies (denoted as TM-M′2TiC2O2−δ , where M′ = Cr or Mo) were calculated, and the results indicated that the introduction of oxygen vacancies can increase the stabilities of TM adatoms. The TM modification on the MXenes surface tuned the Gibbs free energy of hydrogen adsorption G H, and the G H values of Au-, Co-Cr2TiC2O2−δ , and Ni-Mo2TiC2O2−δ closed to zero values (0.07, −0.07, and 0.02 eV, respectively). The presence of TM adatoms also changed the reaction mechanism of H2 desorption and reduced the activation barrier for H2 production to improve the catalytic efficiency. Nine TM-M′2TiC2O2−δ systems were found to have both HER activity and a lower H2 desorption reaction barrier than the pristine MXenes. Systematic electronic structure analyses showed that charge rearrangement through TM modification could tune the number of electrons gained by the surface O atom and have an impact on the hydrogen adsorption strength. These results indicated that TM surface modification is an effective method for improving the HER catalytic activity of double TM carbides.

Impact of hydrogen coverage on silane adsorption during Si epitaxy from ab initio simulations

Epitaxy by Chemical Vapor Deposition (CVD) is a commonly used technique for the growth of Si alloys in microelectronic devices. In this work, we perform Density Functional Theory (DFT) simulations to study the impact of H coverage on the dissociative adsorption of silane on a Si(001) surface. Silane adsorption is systematically found thermodynamically favorable but its kinetics is limited by H2 desorption which exhibits an activation energy of 2.4 eV. In addition, our calculations suggest that hydrogenated surfaces tend to reduce the adsorption activation energies compared to uncovered surfaces. This work provides an atomistic description of the SiH4 adsorption mechanisms and associated energies for the modeling of the epitaxial deposition process using large scale simulation methods.

Superalkali functionalized two-dimensional haeckelite monolayers: A novel hydrogen storage architecture

Exploring efficient storage mediums is the key challenge to accomplish a sustainable hydrogen economy. Material-based hydrogen (H2) storage is safe, economically viable and possesses high gravimetric density. Here, we have designed a novel H2 storage architecture by decorating graphene-like haeckelite (r57) sheets with the super-alkali (NLi4) clusters, which bonded strongly with the r57. We have performed van der Waals corrected density functional theory (DFT) calculations to study the structural, electronic, energetic, charge transfer, and H2 storage properties of one-sided (r57-NLi4) and two-sided (r57-2NLi4) coverage of r57 sheets. Exceptionally high H2 storage capacities of 10.74%, and 17.01% have been achieved for r57-NLi4, and r57-2NLi4 systems, respectively that comfortably surpass the U.S. Department of Energy's (DOE) targets. Under maximum hydrogenation, the average H2 adsorption energies have been found as −0.32 eV/H2, which is ideal for reversible H2 storage applications. We have further studied the effects of mechanical strain to explore the H2 desorption mechanism. Statistical thermodynamic analysis has been employed to study the H2 storage mechanism at varied conditions of pressures and temperatures. Our findings validate the potential of r57-xNLi4 as efficient H2 storage materials.

Enhancement in the hydrogen storage capability of borophene through yttrium doping: A theoretical study

In this study, we conducted first-principles density functional calculations to investigate the effect of Yttrium (Y) doping on β12-Borophene for hydrogen storage. The negative adsorption energy results proved that hydrogen molecules adsorption on Y-doped β12-Borophene (Y@Borophene) monolayer is exothermic and thermodynamically stable. The obtained adsorption energy results proved that the doped Y atoms attached strongly on β12-Borophene surface and don't tend to form a metal cluster. Moreover, results indicate that Y@Borophene can bind up to six hydrogen molecules with an average adsorption energy of −0.141 eV/H2. The adsorption energy results between Y@Borophene complex and hydrogen molecules ranged from −0.133 eV to −0.178 eV which is an acceptable range for an ideal H2 storage material. The Y@Borophene can lead the hydrogen gravimetric density to exceed the 5.5 wt% target of US Department of Energy. Moreover, the obtained electronic properties exhibit the charge transfer which occurred from the Y atom to boron atoms of borophene and from hydrogens to Y atom. The projected density of states (PDOS) analysis verifies the orbital hybridisation which primarily occurs between B-p, H-s, and Y-d orbitals, indicating the potential of hydrogen adsorption capability. Molecular dynamic simulation results confirmed that the desorption temperature range of Y@Borophene is between 186 and 334 K and had a great H2 desorption performance in the ambient temperature that is ideal for vehicle fuel cell operation. Therefore, this theoretical study presents the Y@Borophene is a prospective material for hydrogen storage system.

Design of Bifunctional Nb/V Interfaces for Improving Reversible Hydrogen Storage Performance of MgH2

While MgH2 has been widely regarded as a promising solid‐state hydrogen storage material, the high operating temperature and sluggish kinetics pose a major bottleneck for its practical application. Herein, V4Nb18O55 microspheres composed of nanoparticles with size of tens of nanometers are fabricated to promote H2 desorption and absorption properties of MgH2, which results in the uniform formation of Nb/V interfaces based on a molecular scale during the reversible hydrogen storage process. It is experimentally and theoretically demonstrated that the uniform building of Nb/V interfaces not only preserves the ability of Nb in weakening Mg‐H bonds but also alleviates the strong adsorption capacity of metallic Nb toward hydrogen atoms, leading to a relative energy barrier for the whole dehydrogenation process of MgH2 of only 0.5 eV, which is 0.22 and 0.43 eV lower than that of Nb and V, respectively. As a result, under the addition of V4Nb18O55 microspheres, the onset H2 desorption temperature of MgH2 is decreased to 165 °C, 125 °C lower than that of bulk MgH2, and the complete hydrogenation of Mg could be realized even at room temperature, while almost no H2 adsorption is observed for bulk Mg at a high temperature of 50 °C.