Hydrogen Splitting Research Articles

Hydrogen splitting at a single phosphorus centre and its use for hydrogenation.

Catalytic processes are largely dominated by transition-metal complexes. Main-group compounds that can mimic the behaviour of the transition-metal complexes are of great interest due to their potential to substitute or complement transition metals in catalysis. While a few main-group molecular centres were shown to activate dihydrogen via the oxidative addition process, catalytic hydrogenation using these species has remained challenging. Here we report the synthesis, isolation and full characterization of the geometrically constrained phosphenium cation with the 2,6-bis(o-carborano)pyridine pincer-type ligand. Notably, this cation can activate the H-H bond by oxidative addition to a single PIII cationic centre, producing a dihydrophosphonium cation. This phosphenium cation is also capable of catalysing hydrogenation reactions of C=C double bonds and fused aromatic systems, making it a main-group compound that can both activate H2 at a single molecular main-group centre and be used for catalytic hydrogenation. This finding shows the potential of main-group compounds, in particular phosphorus-based compounds, to serve as metallomimetic hydrogenation catalysts.

Hydrazine Oxidation in Aqueous Solutions I: N4H6 Decomposition

A mixture of nonlabeled (14N2H4) and 15N labeled hydrazine (15N2H4) in an aqueous solution is oxidized to 15N2, 14N2, and 14N15N molecules, indicating the intermediate existence of the 14NH2-14NH-15NH-15NH2 with subsequent hydrogen transfers and splitting of side N-N bonds. The structures, thermodynamics and electron characteristics of various N4H6 molecules in aqueous solutions are investigated using theoretical treatment at the CCSD/cc-pVTZ level of theory to explain the crucial part of the hydrazine oxidation reaction. Most N4H6 structures in aqueous solutions are decomposed during geometry optimization. Splitting the bond between central nitrogen atoms is the most frequent method, but the breakaway of the side nitrogen is energetically the most preferred one. The N-N fissions are enabled by suitable hydrogen rearrangements. Gibbs free energy data indicate the dominant abundance of NH3... N2... NH3 species. The side N atoms have very high negative charges, which should support hydrogen transfers in aqueous solutions. The only stable cyclo-(NH)4…H2 structure has a Gibbs energy that is too high and breaks the H2 molecule. The remaining initial cyclic structures are split into hydrazine and HN≡NH or H2N≡N species, and their relative abundance in aqueous solutions is vanishing.

Metallofullerenes as Robust Single-Atom Catalysts for Adsorption and Dissociation of Hydrogen Molecules: A Density Functional Study.

Hydrogen is currently considered as the best alternative for traditional fuels due to its sustainable and ecofriendly nature. Additionally, hydrogen dissociation is a critical step in almost all hydrogenation reactions, which is crucial in industrial chemical production. A cost-effective and efficient catalyst with favorable activity for this step is highly desirable. Herein, transition-metal-doped fullerene (TM@C60) complexes are designed and investigated as single-atom catalysts for the hydrogen splitting process. Interaction energy analysis (Eint) is also carried out to demonstrate the stability of designed TM@C60 metallofullerenes, which reveals that all the designed complexes have higher thermodynamic stability. Furthermore, among all the studied metallofullerenes, the best catalytic efficiency for hydrogen dissociation is seen for the Sc@C60 catalyst Ea = 0.13 eV followed by the V@C60 catalyst Ea = 0.19 eV. The hydrogen activation and dissociation processes over TM@C60 metallofullerenes is further elaborated by analyzing charge transfer via the natural bond orbital and electron density difference analyses. Additionally, quantum theory of atoms in molecule analysis is carried out to investigate the nature of interatomic interactions between hydrogen molecules and TMs@C60 metallofullerenes. Overall, results of the current study declare that the Sc@C60 catalyst can act as a low cost, highly efficient, and noble metal-free single-atom catalyst to efficiently catalyze hydrogen dissociation reaction.

Diffusion of muonic hydrogen in hydrogen gas and the measurement of the 1$s$ hyperfine splitting of muonic hydrogen

The CREMA collaboration is pursuing a measurement of the ground-state hyperfine splitting (HFS) in muonic hydrogen (\muμp) with 1 ppm accuracy by means of pulsed laser spectroscopy. In the proposed experiment, the \muμp atom is excited by a laser pulse from the singlet to the triplet hyperfine sub-levels, and is quenched back to the singlet state by an inelastic collision with a H_22 molecule. The resulting increase of kinetic energy after this cycle modifies the \muμp atom diffusion in the hydrogen gas and the arrival time of the \muμp atoms at the target walls. This laser-induced modification of the arrival times is used to expose the atomic transition. In this paper we present the simulation of the \muμp diffusion in the H_22 gas which is at the core of the experimental scheme. These simulations have been implemented with the Geant4 framework by introducing various low-energy processes including the motion of the H_22 molecules, i.e. the effects related with the hydrogen target temperature. The simulations have been used to optimize the hydrogen target parameters (pressure, temperatures and thickness) and to estimate signal and background rates. These rates allow to estimate the maximum time needed to find the resonance and the statistical accuracy of the spectroscopy experiment.

Pure phase Ni12P5 anchored on N, P-codoped carbon nanosheet: A stable and highly efficient catalyst to reduce toxic organic compounds for continuous-flow application

The removal of toxic organic compounds from aqueous media through reduction reactions using nonnoble catalysts has attracted much attention in recent years. In this study, a simple method for the synthesis of pure-phase Ni12P5 nanoparticles supported on N, P-codoped carbon (NPC) sheets was developed, in which a nickel phosphine complex was selected as the precursor due to its high Ni/P ratio, air stability and easy preparation. By controlling the pyrolysis temperature, NixPy@NPC700 with a high dispersity and exposed active sites can be obtained, which was characterized by XRD, HRTEM, EDS, XPS, Raman and NH3-TPD. The catalytic performance of the composite in the reaction of 4-nitrophenol (4-NP) was assessed under mild conditions, exhibiting excellent catalytic activity with a low apparent activation energy Ea (29.87 KJ·mol−1). In addition, the catalyst can be recycled without obvious loss of activity for up to ten successive cycles. The outstanding hydrogenation activity is ascribed to the exposed Ni12P5(312) crystal plane of NixPy@NPC700, which is attributed to the lower energy barrier required to form a hydrogen splitting state according to DFT calculations. Moreover, NixPy@NPC700 was creatively coated in a Teflon tube with Nafion as the adhesive and constructed as a fixed-bed device. The continuous-flow catalytic reaction shows that the catalyst can maintain a satisfactory efficiency for approximately 6 h in the reduction of 4-NP and methyl orange (MO). These findings suggest that NixPy@NPC700 is an ideal catalyst for industrial applications for the chemical reduction of toxic compounds from wastewater.

Study of hydrogen absorption in a novel three-dimensional graphene structure: Towards hydrogen storage applications

The use of a novel three-dimensional graphene structure allows circumventing the limitations of the two-dimensional nature of graphene and its application in hydrogen absorption. Here we investigate hydrogen-bonding on monolayer graphene conformally grown via the epitaxial growth method on the (0001) face of a porousified 4H-SiC wafer. Hydrogen absorption is studied via Thermal Desorption Spectroscopy (TDS), exposing the samples to either atomic (D) or molecular (D2) deuterium. The graphene growth temperature, hydrogen exposure temperature, and the morphology of the structure are investigated and related to their effect on hydrogen absorption. The three-dimensional graphene structures chemically bind atomic deuterium when exposed to D2. This is the first report of such an event in unfunctionalized graphene-based materials and implies the presence of a catalytic splitting mechanism. It is further shown that the three-dimensional dendritic structure of the porous material temporarily retains the desorbed molecules and causes delayed emission. The capability of chemisorbing atoms after a catalytic splitting of hydrogen, coupled to its large surface-to-volume ratio, make these structures a promising substrate for hydrogen storage devices.

Three-body interaction effects in heterolytic hydrogen splitting by frustrated Lewis pairs.

The reaction of heterolytic dihydrogen splitting by frustrated Lewis pairs P(R)3 and B(C6F5)3 (where R = t-butyl and 1-adamantene) is driven by strong three-body contributions which originate from the induction and charge transfer effects. The three-body effect increases dramatically as a function of inter-hydrogen distance. As predicted by the symmetry adapted perturbation theory, the "frustration" of Lewis pairs originates from the dual role of the exchange effects. First, the exchange manifests itself in the first-order Pauli repulsion by keeping the pairs away. Second, and equally important, the second-order exchange-induction almost completely cancels the effects of the second-order induction. This suppression of induction effects eases up upon the interaction of the frustrated pairs with H2. The activation of induction in this instance constitutes the three-body effect.

Hydrogen Activation by Frustrated and Not So Frustrated Lewis Pairs Based on Pyramidal Lewis Acid 9-Boratriptycene: A Computational Study.

Structural features and reactivity of frustrated Lewis pairs (FLPs) formed by pyramidal group 13 Lewis acids based on 9-bora and 9-alatriptycene and bulky phosphines P t Bu3, PPh3, and PCy3 are considered at the M06-2X/def2-TZVP level of theory. Classic FLP is formed only in the B(C6Me4)3CH/P t Bu3 system, while both FLP and donor-acceptor (DA) complex are observed in the B(C6F4)3CF/P t Bu3 system. Formation of DA complexes was observed in other systems; the B(C6H4)3CH·P t Bu3 complex features an elongated DA bond and can be considered a "latent" FLP. Transition states and reaction pathways for molecular hydrogen activation have been obtained. Processes of heterolytic hydrogen splitting are energetically more favored in solution compared to the gas phase, while activation energies in the gas phase and in solution are close. The alternative processes of hydrogenation of B-C or Al-C bonds in the source pyramidal Lewis acids in the absence of a Lewis base are exergonic but have larger activation energies than those for heterolytic hydrogen splitting. The tuning of Lewis acidity of 9-boratriptycene by changing the substituents allows one to control its reactivity with respect to hydrogen activation. Interestingly, the most promising system from the practical point of view is the DA complex B(C6H4)3CH·P t Bu3, which is predicted to provide both low activation energy and thermodynamic reversibility of the heterolytic hydrogen splitting process. It appears that such "not so frustrated" or "latent" FLPs are the best candidates for reversible heterolytic hydrogen splitting.

Combined Computational and Experimental Investigation on the Mechanism of CO2 Hydrogenation to Methanol with Mn-PNP-Pincer Catalysts

A theoretical and experimental mechanistic study is presented for the homogeneously catalyzed CO2 hydrogenation to methanol, using an Mn-PNP-Pincer catalyst in the presence of a Lewis acid cocatalyst and alcohol as a solvent. Quantum chemical computations at the density functional theory and DLPNO-CCSD(T) level of theory suggest the presence of a formate resting state as the most stable intermediate. The concerted activation of dihydrogen via a proton shuttle mechanism and decomposition of a hemiacetal intermediate is computed to define the turnover-determining transition state. The resulting energy span is calculated as 34.5 kcal mol–1 at the DLPNO-CCSD(T) level of theory. An Eyring plot reveals the experimental barrier of the reaction at 31.4 kcal mol–1 under catalytic turnover conditions, showing a good agreement with a slight overestimation of the computational model. Concentration–time profiles of the involved species also locate experimentally the rate-determining states (RDSs) of the reaction in the hydrogenation of a formate ester intermediate to methanol. The measured kinetic isotope effects for the use of H2/D2 and EtOH/D are in agreement with hydrogen splitting as the RDS, giving further support to the computed mechanism. These insights provide guidance and reference for future improvement of hydrogenation catalysts based on abundant 3d metals for the CO2-based production of methanol.

Hydrogen production from water using MoX2/ZnO (X:S,Se) heterostructures as photocatalysts

The role of two-dimensional heterostructures (HSs) in clean hydrogen production through photocatalytic water splitting has been paid enormous attention. Herein, we report a HS of transition metal dichalcogenide monolayer MoX2 where X–S,Se and graphene-like zinc oxide (g-ZnO). The structural,electronic, and optical properties have been investigated using density functional theory. MoS2/ZnO shows type-II band alignment with indirect bandgap of 1.61eV, a significant in-built potential of 7.42eV, and a valence band offset of 1.23eV across the interface, while MoSe2/ZnO HS shows type-I band alignment with direct bandgap of 1.80eV, in-built potential of 3.64eV, and a valence band offset of 0.34eV. Bandgap value and band-edge positions proved these HSs to be promising candidates for water splitting and evolution of hydrogen using solar energy. The results suggest the possibility of using 2D MoX2/ZnO HS as potential photocatalysts for straddling the redox potentials of water over a wide range, from ultraviolet to infrared spectra. The photogenerated charge carriers in the MoS2/ZnO HS are localized in different layers and can efficiently generate hydrogen energy by photocatalytic water splitting. However, the band-edge positions in MoSe2/ZnO are more suitable for pH = 8, making it promising photocatalyst for large-scale hydrogen production from solar energy.

The Proton Structure in and out of Muonic Hydrogen

Laser spectroscopy of muonic atoms has been recently used to probe properties of light nuclei with unprecedented precision. We introduce nuclear effects in hydrogen-like atoms, nucleon structure quantities (form factors, structure functions, polarizabilities), and their effects in the Lamb shift and hyperfine splitting (HFS) of muonic hydrogen (μH). Updated theory predictions for the Lamb shift and HFS in μH are presented. We review the challenges of the ongoing effort to measure the ground-state HFS in μH and its impact on our understanding of the nucleon spin structure. To narrow down this search, we present a novel theory prediction obtained by scaling the measured HFS in hydrogen while leveraging radiative corrections. We also summarize recent developments in the spectroscopy of simple atomic and molecular systems and emphasize how they allow for precise determinations of fundamental constants, bound-state QED tests, and New Physics searches.

Activation of H2S by Atomic Cr, Mn, and Fe: Matrix Infrared Spectra and Quantum Chemical Calculations.

Hydrogen sulfide is toxic and corrosive gas abundantly available in nature. The activation of hydrogen sulfide to produce hydrogen and elemental sulfur is of great significance for possible applications in toxic pollutant control and hydrogen energy regeneration. The activation of H2S by transition metal atoms (M = Cr, Mn, and Fe) has been studied by low-temperature matrix isolation infrared spectroscopy and quantum chemical calculations. Experimental and theoretical results indicate that the reaction between ground-state M atoms and H2S is inhibited by the repulsive interactions between the reactants. After being excited upon photolysis, the corresponding excited-state M atoms react with H2S molecules spontaneously. The produced insertion product HMSH further decomposed to metal sulfides upon full-arc mercury lamp irradiation by the splitting of hydrogen.

Photocatalytic hydrogen production using graphitic carbon nitride (GCN): A precise review

The positive feedback mechanism resulting from the exponentially increasing population leads to high energy demands, additional resource utilization, and debilitating nature, making the earth an unsustainable habitat for living. The resulting increase in global temperature, also leads to an increased carbon footprint, creating a chain of events called loop functioning or positive feedback chain. The renewable energy-driven water splitting and generation of hydrogen, which is further used as a clean fuel, serves as a sustainable route for satisfying the over enhanced energy demand and also helps in reducing the global carbon footprint by minimizing the resulting emission. The recent advancement in the photo catalytic systems, especially introduction of advance photocatalysts in the last decade, serves the path more enviably. The photocatalysts involved in the process of hydrogen production and using renewable energy as a driving force, especially solar energy, should remain unaltered. The desired changes in the catalytic activity, separation and conveying of charges at its surface are further catalysed by the solar energy. With technological advancement, novel and cost-effective hydrogen production mechanisms are evolving. This search for a cheaper, effective and sustainable photocatalyst material, which effectively splits the water molecules into desirable hydrogen isotopes is the need of the hour to sustain the ever growing energy demands. And in all this pursuit, a metal-free, suitable bandgap energy, cost-effective and 2D structured compound known as graphitic carbon nitride (GCN or g-C3N4) serves as a potential contender by effective splitting and efficient production of hydrogen. But GCN, even having so much potential, undergoes some challenges such as high density of defects, required surface area and desirable stability that restrict its photocatalytic activity and resulting water splitting efficiency. The present review addresses the latest trends in the composition variabilities in GCN that helps in increased splitting efficiency, doping with metallic particles, heterojunction formation in semiconductors, pore size-perviousity changes, modulation of the bandgap, control of defects and alteration in the surface area. This review also highlights the peak development and changes in the design and morphology of GCN under larger surface area performance and corresponding advancements in hydrogen production. Although not all renewable energy sources are considered; in this review, the photocatalytic production of hydrogen using the solar energy-driven channel is the primary highlight. Further, the concluding portion of this review helps the readers/scientific community to get a clear idea about photocatalytic hydrogen production and its derived routes, which also serve as an inoculum for future studies in the same domain.

Statistical Optimization and Modeling Approach for Fenton‐like Discoloration of Methyl Orange using Green Zero‐valent Iron Nanoparticle Catalysts

AbstractWastewater treatment is extremely beneficial to the environment by minimizing pollution. Water pollution caused by textile industries deteriorates ecosystems and threatens the environment. In this study, we fabricated nanoscale zerovalent iron nanoparticle (NZVI‐NPs) catalysts that act as Fenton‐like adsorbents, which remove methyl orange (MO) dye from wastewater much faster than microscale nanoparticles. The analysis of variance (ANOVA) led us to derive a quadratic model with R2=0.973. According to the central composite design in response surface methodology (CCD‐RSM) statistical optimization, 99.65 % of predicted decolorization was achieved with 1.0 g/L catalyst loading, pH initialization of 3.0, reaction temperature of 25 °C, and 22 mmol/L H2O2 concentration. By fitting a pseudo‐second‐order kinetic model, we calculated the rate constant of dye adsorption. The Langmuir isotherm demonstrated an excellent correlation between dye adsorption and catalyst with a maximum adsorption capacity (50.45 mg/g). The activation energy of the catalyst (62.26 kJ/mol) predicts a physical adsorption process. Newly developed catalysts are green efficient adsorbents suitable for significant dye removal from wastewater for the safety of aquatic life and human life. Moreover, these newly developed materials could be more suitable for the remediation of other harmful pollutants and the production of hydrogen, energy and water splitting applications.

Axial-vector exchange contribution to the hyperfine splitting

We revisit the contribution of axial-vector mesons to the hyperfine splitting of muonic hydrogen. We focus our attention on the doubly-virtual asymptotic behavior of the relevant form factors of axial-vector mesons, together with their coupling to nucleons based on resonance saturation and short-distance constraints. Among others, we find significant differences with respect to previous studies, including an opposite sign and a $\sim50\%$ effect of the doubly-virtual high-energy behavior.

Lattice-Resolution, Dynamic Imaging of Hydrogen Absorption into Bimetallic AgPd Nanoparticles.

Palladium's strong reactivity and absorption affinity to H2 makes it a prime material for hydrogen-based technologies. Alloying of Pd has been used to tune its mechanical stability, catalytic activity, and absorption thermodynamics. However, atomistic mechanisms of hydrogen dissociation and intercalation are informed predominantly by theoretical calculations, owing to the difficulty in imaging dynamic metal-gas interactions at the atomic scale. Here, we use in situ environmental high resolution transmission electron microscopy to directly track the hydrogenation-induced lattice expansion within AgPd triangular nanoprisms. We investigate the thermodynamics of the system at the single particle level and show that, contrary to pure Pd nanoparticles, the AgPd system exhibits α/β coexistence within single crystalline nanoparticles in equilibrium; the nanoparticle system also moves to a solid-solution loading mechanism at lower Ag content than bulk. By tracking the lattice expansion in real time during a phase transition, we see surface-limited β phase growth, as well as rapid reorientation of the α/β interface within individual particles. This secondary rate corresponds to the speed with which the β phase can restructure and, according to our atomistic calculations, emerges from lattice strain minimization. We also observe no preferential nucleation at the sharpest nanoprism corners, contrary to classical nucleation theory. Our results achieve atomic lattice plane resolution─crucial for exploring the role of crystal defects and single atom sites on catalytic hydrogen splitting and absorption.

CFD Simulation of Hydrogen Generation and Methane Combustion Inside a Water Splitting Membrane Reactor

Hydrogen production from water splitting remains difficult due to the low equilibrium constant (e.g., Kp ≈ 2 × 10−8 at 900 °C). The coupling of methane combustion with water splitting in an oxygen transport membrane reactor can shift the water splitting equilibrium toward dissociation by instantaneously removing O2 from the product, enabling the continuous process of water splitting and continuous generation of hydrogen, and the heat required for water splitting can be largely compensated for by methane combustion. In this work, a CFD simulation model for the coupled membrane reactor was developed and validated. The effects of the sweep gas flow rate, methane content and inlet temperature on the reactor performance were investigated. It was found that coupling of methane combustion with water splitting could significantly improve the hydrogen generation capacity of the membrane reactor. Under certain conditions, the average hydrogen yield with methane combustion could increase threefold compared to methods that used no coupling of combustion. The methane conversion decreases while the hydrogen yield increases with the increase in sweep gas flow rate or methane content. Excessive methane is required to ensure the hydrogen yield of the reactor. Increasing the inlet temperature can increase the membrane temperature, methane conversion, oxygen permeation rate and hydrogen yield.

Potential of magnetic nano cellulose in biomedical applications: Recent Advances

Biopolymers have attracted considerable attention in various biomedical applications. Among them, cellulose as sustainable and renewable biomass has shown potential efficacy. With the advancement in nanotechnology, a wide range of nanostructured materials have surfaced with the potential to offer substantial biomedical applications. . The progress of cellulose at the nanoscale regime (nanocelluloses) with diverse forms like cellulose nanocrystals, nanofibres and bacterial nanocellulose) has imparted remarkable properties like high aspect-ratio and high mechanical strength, and biocompatibility. The amalgamation of nanocellulose together with magnetic nanoparticles (MNC) could be explored for a synergistic effect. In this review, a brief introduction of nano cellulose , magnetic nanoparticles and the synergistic effect of MNC is described. Further, the review sheds light on the recent studies based on MNCs with their potential in the biomedical area. Finally, the review is concluded by citing the remarkable value of MNC with their futuristic applications in other fields like friction layers for triboelectric nanogenerator (TENG), energy production, hydrogen splitting, and wearable electronics.

Visible-Light-Harvesting Hedgehog like Copper Bismuth Oxide: Optical, Structural and Electrochemical Properties

Synthesize of materials with desired properties such as harvest wide range of solar spectrum including visible light and better charge transport properties preferred due to its many potential applications such as water hydrogen splitting, photocatalytic dye degradation and photovoltaic application etc. In this present study the CuBi2O4 material successfully synthesized by solution based synthesize method, followed by dried at 150°C and sintered at various temperature such as 300°C, 400°C and 500°C and the variation of its’ optical, structural and electrochemical properties were analyzed. The sample sintered at 500°C exists in pure form and there are no identified incomplete phases of CuO and Bi2O3. However, the sample sintered at higher temperature shows higher charge transfer resistance between electrode-electrolyte interface. CuBi2O4 sintered at lower temperature shows better charge transfer characteristic due to formation of small size of crystal and existence of different incomplete phases of CuBi2O4 such as CuO and Bi2O3 etc. However, the sample sintered at high temperature showed better characteristic properties for visible light-driven photocatalyst such as enhanced in crystallinity, low dislocation density, and enhanced absorption in visible region of the spectrum. Therefore, the higher sintered temperature is more suitable to synthesize the visible light-driven CuBi2O4 photocatalyst.

Solid micellar Ru single-atom catalysts for the water-free hydrogenation of CO2 to formic acid

The catalytic hydrogenation of CO2 to formic acid is one of the most promising pathways towards a renewable hydrogen-storage system. The reaction is usually performed in aqueous phase in the presence of basic molecules over homogeneous or heterogeneous catalysts, generating relatively dilute formate solutions (<1 M).The newly designed solid micellar Ru single-atom catalyst enables efficient and stable water-free CO2 hydrogenation to formate under mild reaction conditions. Concentrated formate solutions (up to 4 M) are produced directly from the hydrogenation of carbon dioxide in water-free tertiary amine. In the catalyst, Ru(III) single sites are incorporated into the walls of MCM-41 during hydrolysis creating a solid micelle structure. The presence of the CTA+ surfactant in the pores of MCM-41 stabilizes the Ru sites and prevents catalyst deactivation. DFT modelling suggests that the reaction proceeds via heterolytic hydrogen splitting, forming a Ru-H species and subsequent hydride transfer to CO2.