Hydrogen Affinity Research Articles

Extraction of rare earth elements from ion adsorption clay using bio-based ionic liquid via COSMO-RS: computational and experimental validation

The study introduces eco-friendly leaching agents as alternatives to traditional rare earth element (REE) extraction solvents, addressing environmental concerns associated with ammonium sulfate. Bio-based ionic liquids (ILs), known for their non-toxic and biodegradable properties, were screened using the COSMO-RS software. Initially, 105 ILs involving 7 cations and 15 anions were computationally screened to find the best ILs for REE extraction. The chosen criteria were based on hydrogen bond formation, affinity screening, hydrophobicity, viscosity, and eco-toxicity test. Based on the COSMO-RS screening, choline oleate, choline decanoate, and choline hexanoate exhibit high solubility for REEs, with a chemical potential of 17.60, 17.01, and 18.37 kcal/mol at REE oxidation state +2. Choline glycinate, choline oleate, choline decanoate, choline hexanoate, choline lysinate, and choline leucinate were selected for their strong affinity to extract REE dissociate ions. Experimental results show slightly higher REE extraction from ammonium sulfate (3.17 ppm) compared to choline glycinate (3.15 ppm). For long-term applications, choline glycinate offers a promising eco-friendly and cost-effective alternative to traditional leaching agents, promoting economic feasibility and environmental friendliness.

Rare-Earth Metal-Based Materials for Hydrogen Storage: Progress, Challenges, and Future Perspectives.

Rare-earth-metal-based materials have emerged as frontrunners in the quest for high-performance hydrogen storage solutions, offering a paradigm shift in clean energy technologies. This comprehensive review delves into the cutting-edge advancements, challenges, and future prospects of these materials, providing a roadmap for their development and implementation. By elucidating the fundamental principles, synthesis methods, characterization techniques, and performance enhancement strategies, we unveil the immense potential of rare-earth metals in revolutionizing hydrogen storage. The unique electronic structure and hydrogen affinity of these elements enable diverse storage mechanisms, including chemisorption, physisorption, and hydride formation. Through rational design, nanostructuring, surface modification, and catalytic doping, the hydrogen storage capacity, kinetics, and thermodynamics of rare-earth-metal-based materials can be significantly enhanced. However, challenges such as cost, scalability, and long-term stability need to be addressed for their widespread adoption. This review not only presents a critical analysis of the state-of-the-art but also highlights the opportunities for multidisciplinary research and innovation. By harnessing the synergies between materials science, nanotechnology, and computational modeling, rare-earth-metal-based hydrogen storage materials are poised to accelerate the transition towards a sustainable hydrogen economy, ushering in a new era of clean energy solutions.

Development of Ti–Zr–Mn–Cr-(V–Fe) based alloys for hydrogen feeding system in hydrogen metallurgy application

AB2-type Ti-based hydrogen storage alloys are considered promising candidates for the hydrogen feeding system in hydrogen-metallurgy application. In this work, Ti0·87Zr0.15MnxCr1.75-xV0.25 (x = 1.25–1.5), Ti0·87Zr0·15Mn1·5Cr0.5-y(VFe)y (y = 0.25–0.43) and Ti0.85+zZr0.15Mn1·5Cr0·07(VFe)0.43 (z = 0–0.05) alloys were synthesized using induction levitation melting, where ferrovanadium VFe consists of 80 wt% V and 20 wt% Fe. Subsequently, their microstructures and hydrogen storage performances were systematically investigated. The results demonstrate that all alloy samples exhibit a single C14 Laves phase structure with uniform element distribution. With the increment of Cr/Mn, VFe/Cr ratio, or Ti stoichiometry, the alloys exhibit enhanced hydrogen storage capacity, accompanied by a decrease in hydrogenation equilibrium pressure because of interstitial volume expansion or hydrogen affinity improvement, which is also supported by density functional theory calculations. Considering the application of hydrogen metallurgy, Ti0·86Zr0·15Mn1·5Cr0·07(VFe)0.43 alloy is regarded as a promising candidate, exhibiting a saturated capacity of 2.01 wt% H2, an effective reversible capacity of 1.91 wt% H2, rapid hydrogenation kinetics, excellent cyclic durability and low costs. This work provides valuable insights into the compositional design of hydrogen storage alloys for the hydrogen feeding system in hydrogen metallurgy applications.

Self-assembled chromium-based nitrogen carrier for chemical looping ammonia synthesis

Industrially, ammonia is generated mainly using the energy-intensive and CO2-emitting Haber-Bosch process, which is not conducive to sustainable economic and social development. The chemical looping ammonia synthesis (CLAS) is capable of coupling green energy, which is one of the available alternatives to the Haber-Bosch process, but the ammonia production rate of most of its nitrogen carriers is unsatisfactory. In this work, we designed a self-assembled nitrogen carrier using ZSM-5 molecular sieve (ZSM-5) and nickel (Ni) to modify chromium nitride (CrN). ZSM-5 molecular sieves have a rich pore structure, which enables the gas-phase reactants to react with the lattice nitrogen in the subsurface layer of the nitrogen carrier. Nickel can facilitate the dissociation of hydrogen during hydrogenation due to its higher hydrogen affinity. The ammonia production rate of the nitrogen carrier can reach 451.2 μmol g−1 h−1 at 700 °C and atmospheric pressure, and be able to remain 358 μmol g−1 h−1 after eight cycles. Furthermore, we also propose a full-coverage design strategy for nitrogen carriers: simultaneous optimization of the chemical and mass transfer processes in the nitrogen carrier. This work advances the design of high-performance nitrogen carrier, thus facilitating the applications of CLAS for the distributed ammonia synthesis.

Sorption properties of nanostructured ball-milled porous silicon for solid-state hydrogen storage up to 80 bar

Solid-state storage is a feasible solution to store hydrogen compared to commercially available techniques. The disadvantage of using metal and complex hydrides for storage is the elevated temperature operation (>400 °C) and slow reaction kinetics. Porous materials like carbon nanostructures, metal-organic frameworks, zeolites, and porous polymers possess high surface energy and hydrogen affinity. However, cryogenic temperature operation and low storage at ambient conditions are major limitations for practical storage applications. Modifying the material morphology and storage parameters to enhance hydrogen storage is under intense investigation. This study focuses on nanostructuring porous silicon (PS), evaluating its structural characteristics, and investigating its ability to store hydrogen at up to 80 bar. The challenges of large particle size and low-pressure hydrogen storage in the novel porous material is addressed with possible mechanisms. The discussion explored the potential of utilizing interconnected pores via nanoscale engineering and increased charging pressure to optimize hydrogen exposure. Nanostructuring the hand-grinded porous Si (HGPS) reduces crystallite size, boosts surface energy and enhances thermodynamics. At 80 bar and 120 °C, the ball-milled PS (BMPS) exhibits a hydrogen storage capacity of 10.7 wt%. The isosteric heat of adsorption is utilized to optimize storage conditions to achieve useable capacity. The hydrogen adsorption pressure is optimized between 40 and 60 bar, where the storage capacity ranges from 2 wt% and 6 wt% (meeting the hydrogen storage target set by the US Department of Energy). X-ray Photoelectron Spectroscopy investigates surface states and bonding involving silicon hydrides. The effect of nanostructuring on decomposition energy is observed by differential scanning calorimetry. The decreased crystallite size, examined through X-ray diffraction and Raman spectroscopy, exposes nanopores accessible to hydrogen. The accessibility enhances storage capacity in free and surface-affixed states, rendering BMPS for reversible storage applications. The lower temperature requirement for hydrogen adsorption and release from storage material aligns with Sustainable Development Goal 7 (SDG 7) on affordable and clean energy.

Amorphous-crystalline transition-driven synthesis of Co single-atom catalysts on MoO3 for enhanced hydrogen evolution in acidic and alkaline media

Single atom catalysts (SACs) dispersed in metal oxide supports offer not only maximized catalyst utilization but also extended modulation capabilities through interactions between the SA and its support. However, achieving facile preparation and ensuring electrochemical durability of such SACs, particularly for hydrogen evolution reaction (HER) applications, remain formidable challenges. Our study addresses these issues by employing an amorphous-to-crystalline phase transition in MoO3 to synthesize a cobalt (Co) SA catalyst. This method facilitates the production of highly selective SA catalysts at low temperatures and ensures their enhanced stability in HER applications. The Co SA MoO3 catalyst exhibits superior performance in HER, operating effectively in both acidic and alkaline environments. Significantly, it maintains stable HER activity across these diverse electrolytic conditions. Our Density Functional Theory (DFT) calculations provide insights into the exceptional HER performance of Co SA MoO3. These calculations reveal that the strong affinity for hydrogen and water, facilitated by the modulation of the p-band orbitals at specific oxygen sites adjacent to the Co SA, establishes a thermoneutral pathway for HER. This study represents a pivotal advancement, showcasing a highly practical and robust single-atom catalyst, marking a significant stride towards sustainable energy solutions.

Potassium promoter regulates electronic structure and hydrogen spillover of ultrasmall Ru nanoclusters catalyst for ammonia synthesis

The effects of promoters on Ru nanoparticles (≥2 nm) catalysts for NH3 synthesis have been extensively elaborated, but their roles on ultrasmall Ru nanoclusters (NCs, 1–2 nm) remain largely unknown and need to be further uncovered. Herein, a series of K-promoted MgO supported Ru NCs were synthesized and investigated for NH3 synthesis. The addition of 5wt.%K onto Ru/MgO NCs leads to a significantly high NH3 synthesis rate of 21.7 mmolNH3 gcat−1h−1 at 400 °C and 0.2 MPa, close to the thermodynamic equilibrium. Out studies reveal that anchoring K onto Ru NCs can increase the electron density and cause an upshift of the d-band center of Ru entities. Moreover, the addition of K regulates the hydrogen affinity and accelerates the migration of hydrogen from the Ru NCs surface to MgO support, which is crucial in avoiding the hydrogen poisoning effect on Ru NCs. With the synergistic effect of the Ru NCs sites bridged by H-spillover, makes the K-mediated Ru/MgO NCs catalysts efficient for NH3 synthesis at mild conditions.

Sulphur-Boosted Active Hydrogen on Copper for Enhanced Electrocatalytic Nitrate-to-Ammonia Selectivity.

Electrocatalytic nitrate reduction to ammonia is a promising approach in term of pollutant appreciation. Cu-based catalysts performs a leading-edge advantage for nitrate reduction due to its favorable adsorption with *NO3. However, the formation of active hydrogen (*H) on Cu surface is difficult and insufficient, leading to the significant generation of by-product NO2 -. Herein, sulphur doped Cu (Cu-S) is prepared via an electrochemical conversion strategy and used for nitrate electroreduction. The high Faradaic efficiency (FE) of ammonia (~98.3 %) and an extremely low FE of nitrite (~1.4 %) are achieved on Cu-S, obviously superior to its counterpart of Cu (FENH3: 70.4 %, FENO2 -: 18.8 %). Electrochemical in situ characterizations and theoretical calculations indicate that a small amount of S doping on Cu surface can promote the kinetics of H2O dissociation to active hydrogen. The optimized hydrogen affinity validly decreases the hydrogenation kinetic energy barrier of *NO2, leading to an enhanced NH3 selectivity.

Sulphur‐Boosted Active Hydrogen on Copper for Enhanced Electrocatalytic Nitrate‐to‐Ammonia Selectivity

AbstractElectrocatalytic nitrate reduction to ammonia is a promising approach in term of pollutant appreciation. Cu‐based catalysts performs a leading‐edge advantage for nitrate reduction due to its favorable adsorption with *NO3. However, the formation of active hydrogen (*H) on Cu surface is difficult and insufficient, leading to the significant generation of by‐product NO2−. Herein, sulphur doped Cu (Cu−S) is prepared via an electrochemical conversion strategy and used for nitrate electroreduction. The high Faradaic efficiency (FE) of ammonia (~98.3 %) and an extremely low FE of nitrite (~1.4 %) are achieved on Cu−S, obviously superior to its counterpart of Cu (FENH3: 70.4 %, FENO2−: 18.8 %). Electrochemical in situ characterizations and theoretical calculations indicate that a small amount of S doping on Cu surface can promote the kinetics of H2O dissociation to active hydrogen. The optimized hydrogen affinity validly decreases the hydrogenation kinetic energy barrier of *NO2, leading to an enhanced NH3 selectivity.

Computational Design for Enhanced Hydrogen Storage on the Newly Synthesized 2D Polyaramid via Titanium and Zirconium Decoration.

2D polyaramid (2DPA) is a porous and polymeric material that has been synthesized recently. Titanium and zirconium decoration over 2DPA increases their affinity for hydrogen substantially, making them suitable for onboard and reversible hydrogen storage, particularly in light-duty vehicles. By decorating a single unit cell of 2DPA with two transition metal (TM) atoms, hydrogen storage of up to 6.422 and 6.792 wt % of H2 with average binding energies of -0.399 and -0.480 eV is predicted for 2DPA + Ti and 2DPA + Zr, respectively. The binding of Ti and Zr with 2DPA is accompanied by a flow of charge (-1.474e for Ti and -1.696e for Zr) from the TM toward the 2DPA sheet. Further, the interaction between H2 and the TM may proceed via Kubas interaction between the d orbital of the TM in 2DPA + TM and H 1s orbitals of H2, with a net flow of charge from the TM toward H2 (-0.218e for Ti and -0.391e for Zr). The desorption of H2 bound to 2DPA + Zr is endothermic (∼0.57 eV) and close in magnitude to the binding energy of the first H2 (∼-0.544 eV). The 2DPA + TM systems show structural and dynamic stability at high temperatures, as evident from ab initio molecular dynamics simulations and phonon spectra. The movement of TM atoms across the 2DPA sheet to form clusters may be hindered by the considerable barrier energy (∼4.9 eV for Ti). Through these systematic density functional theory simulations, we predict that Ti- and Zr-decorated 2DPA are high-performance hydrogen storage materials and can be explored by experimentalists.

Synthesis of high-entropy alloy nanoparticles using microwave-assisted reduction and investigation of their enhanced electrochemical hydrogen evolution activity

Abstract High-entropy alloys (HEAs) are fascinating materials for novel catalysts because of their broad compositional space, which is enabled by entropy-driven mixing. Herein, HEA nanoparticles (NPs) containing Fe, Co, Ni, Cu, and Pd were successfully synthesized on reduced graphene oxide (rGO) by microwave-assisted reduction. Compared with the corresponding monometallic catalysts, the quinary FeCoNiCuPd/rGO demonstrated greater electrocatalytic activity toward the acidic hydrogen evolution reaction. Density functional theory calculations revealed that modification of the d-band center and the hydrogen affinity induced by multielemental mixing enhanced the electrocatalytic performance of the HEA.

Post O2 Plasma-Induced Fabrication of 1T-WS2/a-WO3 Heterostructure for Superior Hydrogen Evolution Reaction Electrocatalysts Via Hydrogen Spillover

2D transition metal dichalcogenide (TMDC) group has been widely spotlighted as hydrogen evolution reaction (HER) electrocatalysts to replace the conventional Pt electrocatalyst due to their distinctive features of robustness, low cost, and accessibility to structural modification. However, the electrochemical activity of TMDC materials is mostly originated from its exposed edge sites, whereas its basal plane is relatively inert. There have been attempts to increase the relative fraction of active edge sites in the basal plane or employ the phase transition from semiconductive 2H phase to metallic 1T phase. The practical uses have been restricted compared to nobel metal Pt.Plasma engineering is a facile method to functionalize their basal plane and generate vacancies into the lattice as active sites to improve electrocatalytic activity. In our previous works, MoS2 and WS2 has been synthesized to have abundant defects with maximized active edge sites to impart superior HER performance by employing Ar+H2S plasma treatment on tungsten (W) thin metal film with a thickness of 1 nm. However, to surpass the intrinsic electrochemical properites, we introduce 1T-WS2/a-WO3 (WSO) heterostructure via post O2 plasma treatment by exploiting a plasma enhanced-chemical vapor deposition (PE-CVD). There has been a limitation in obtaining the best electrocatalytic performances from the plasma assisted 1T-WS2 films because of its much lower hydrogen affinity of 1T-WS2. On the contrary, tungsten trioxide (WO3) shows strong hydrophilic property in that W atomic site of WO3 can easily absorb H2O. In this regard, 1T-WS2 with hydrophilic amorphous WO3 (a-WO3) can have the outstanding HER activity by inducing hydrogen spillover effect that is a hydrogen transport phenomenon from a-WO3 to 1T-WS2. a-WO3, which has relatively stronger hydrogen affinity, plays an important role in transferring the absorbed hydrogen to 1T-WS2 as active sites. As a result, the HER performance of WSO thin film can be optimized by means of controlling the amount of a-WO3 depending on the post O2 plasma treatment time. It was also confirmed from density functional theory (DFT) calculation that the hydrogen movement on the WSO surface related to hydrogen absorption energy difference between 1T-WS2 and WO3.

Increasing the HER efficiency of photodeposited metal nanoparticles over TiO2 using controlled periodic illumination

Although the use of noble metal catalysts can increase the efficiency of hydrogen evolution reaction, the process is still limited by the characteristics of the metal-hydrogen (M−H) bond, which can be too strong or too weak, depending on the metal employed. Studies revealed that the hydrogen affinity for the metal surface (i.e. H absorption/desorption) is regulated also by the potential at the metal nanoparticles. Through controlled periodic illumination (CPI) of a series of metal/TiO2 suspensions, here we demonstrated that an increase of the HER efficiency is possible for those photodeposited metals which have a Tafel slope below 125 mV. Two possible explanations are here reported, in both of them the M−H interaction and the metal covering level play a prominent role, which also depend on the prevailing HER mechanism (Volmer-Heyrovsky or Volmer-Tafel).

Annealing cracking in Zr and a Zr-alloy with low hydrogen concentration

Hydrogen embrittlement, also known as hydrogen-induced cracking, is a longstanding concern for zirconium (Zr) and its alloys. The affinity for hydrogen in zirconium results in the formation of brittle hydrides. Hydrides are conventionally thought to facilitate crack propagation, and the prevailing recommendation to hinder hydride embrittlement involves reducing the hydrogen concentration in the material and applying slow cooling to reduce thermal stresses. Here, in Zr with a maximum hydrogen concentration of 43 wppm, we show that cracks initiate unexpectedly after annealing, a step that involves slow cooling and no external stress. With a suite of high-resolution microscopy, we show that annealing cracks initiate at prismatic δ-hydrides, whose presence is unexpected. The microscopic annealing crack paths are consequently crystallographic, following the habit plane of these prismatic δ-hydrides. The commonly reported γ-hydride and δ-hydrides that develop on the basal plane are found not to initiate cracks. We rationalize that prismatic δ hydrides result from the intergranular thermal residual stresses that develop during slow cooling. This finding of uncommon annealing cracking further advances the mechanistic understanding of hydride embrittlement in zirconium and can lead to new strategies for design and fabrication of advanced zirconium alloys for harsh environments.

Critical role of initial multi-phase microstructure on the phase transformations during hydrogenation in Fe–Mo alloy system

Given Fe is a low-cost earth-abundant element, there is a need to develop novel Fe-based metal hydrides. The conventional Fe-based hydrides consist of at least one metal with high hydrogen affinity. To synthesize novel low-affinity Fe-based hydrides, the high-pressure and high-temperature method is currently being used. The microstructure is known to influence the de-/hydrogenation processes in metal hydrides. However, in the context of low-affinity Fe-based hydrides, the role of the initial multi-phase microstructure is unknown, which is the objective of the current work. We investigate three as-cast Fe–Mo binary alloys: Fe0.33Mo0.67, Fe0.5Mo0.5, and Fe0.67Mo0.33. Firstly, we first explain in detail the formation mechanisms of the non-equilibrium initial as-cast microstructures caused by the sluggish diffusion of Mo. Subsequently, we present the phase transformations and microstructure evolution during the hydrogenation, depressurization, and aging of Fe–Mo alloys. We demonstrate that each phase in the initial microstructure act as an independent phase during hydrogenation.

Microenvironmental corrosion and hydrolysis induced two-dimensional heterojunction of copper oxide@ferriferrous oxide for efficient electrochemical nitrate reduction to ammonia

Electrochemical nitrate reduction (NO3RR) to ammonia could realize the green synthesis of ammonia and remove nitrate pollutant, which is of great significance to alleviate energy crisis and environmental problem. However, low ammonia selectivity and Faradic efficiency limits its further development. Herein, copper oxide @ ferriferrous oxide heterojunction (CuO NWAs@Fe3O4) was constructed by the in-situ growth of Cu(OH)2 nanowire arrays (Cu(OH)2 NWAs), microenvironmental corrosion and hydrolysis of Fe(NO3)3, and high-temperature pyrolysis. Because of CuO NWAs with excellent adsorption/activation of nitrate and Fe3O4 with high affinity for atomic hydrogen, the heterojunction demonstrated significantly improved NO3RR performance with nitrate conversion rate of 95.93%, ammonia selectivity of 88.68%, Faradaic efficiency of 97.46% and ammonia yield rate of 1.691 mmol h−1 cm−2 at −0.27 V vs. RHE. Moreover, this heterojunction displayed excellent durability with a high Faradaic efficiency of 94.45% after consecutive six cycles and a wide application range from 600 ppm to 2000 ppm. This work will lay the foundation for the design and fabrication of high-performance electrocatalysts for NO3RR.

Achieving Highly Proton-Resistant Zn-Pb Anode through Low Hydrogen Affinity and Strong Bonding for Long-Life Electrolytic Zn//MnO2 Battery.

High-energy electrolytic Zn//MnO2 batteries show potential for grid-scale energy storage, but the severe hydrogen evolution corrosion (HEC) caused by acidic electrolytes results in subdued durability. Here, we report an all-around protection strategy for achieving stable metal Zn anode. Firstly, a proton-resistant Pb-containing (Pb and Pb(OH)2) interface is constructed on Zn anode (denoted as Zn@Pb), which will in-situ form PbSO4 during H2SO4 corrosion and protect the Zn substrate from HEC. Secondly, to improve the plating/stripping reversibility of Zn@Pb, Pb(CH3COO)2 additive (denoted as Zn@Pb-Ad) is introduced, which will convert to PbSO4 precipitation and release trace Pb2+ that can dynamically deposit Pb layer on Zn plating layer to suppress HEC. The superior HEC resistance stems from the low affinity of PbSO4 and Pb for H+ as well as strong bonding between Pb-Zn or Pb-Pb, which increase the hydrogen evolution reaction overpotential and the H+ corrosion energy barrier. Consequently, the Zn@Pb-Ad//MnO2 battery runs stably for 630 and 795h in 0.2 and 0.1M H2SO4 electrolytes, respectively, which are >40 times than that of bare Zn. The as-prepared A h-level battery achieves the one-month calendar life, opening the door to the next generation of high-durable grid-scale Zn batteries. This article is protected by copyright. All rights reserved.

Hydrogen adsorption on magnesium-decorated (3, 3) and (5, 0) boron nitride nanotubes

Hydrogen is one of the cleanest ways to store energy in a post-fossil fuel economy. However, it can be dangerous as bulk gas and additional methods for hydrogen storage are needed. Physisorption on graphene sheets and nanotubes has been proposed as an effective approach due to their exceedingly high surface area and storage capacity similar to, or exceeding, highly compressed gas. Magnesium-doping has been demonstrated to significantly enhance hydrogen storage on boron-doped graphene sheets, but Mg-doped boron nitride nanotubes (BNNT), a potentially far more promising material due to the inherent dipoles in the surface providing stronger affinity for hydrogen, remain unexplored. In this in silico investigation, both the armchair (3,3) and zigzag (5,0) BNNT architectures, doped with Mg atoms, were examined for hydrogen storage capacity using first-principles density functional theory. Our calculations revealed that highly Mg-doped armchair and zigzag polymorphs of BNNTs could adsorb up to 9.65 and 8.77 weight percent hydrogen respectively, above the targets sought by the US Department of Energy for future hydrogen storage materials.

Methanol Synthesis on Copper-Doped F Centers

We investigate the influence of single copper atoms adsorbed at F centers on the KCl (100) surface on the reaction of adsorbed hydrogen and carbon monoxide with density functional theory methods. Adsorption at an F center strongly stabilizes and reduces the copper atom, as its 4s electron pairs with the defect electron to form a closed-shell state. The Cu-doped F center readily reduces adsorbed formaldehyde and strongly interacts with carbon monoxide and methanol, weakening and activating intramolecular bonds, but unlike the empty F center, it does not dissociate methanol. During hydrogenation of adsorbed CO and CH3OH, hydrogen reacts with the adsorbed copper atom to form a stable linear HCuH complex. The hydrogen affinity of the copper atom facilitates the reaction of adsorbed molecules with hydrogen molecules as well as the attachment and removal of hydrogen atoms, enabling a fast synthesis route from carbon monoxide to methanol. The rate-limiting step of the reaction is the final hydrogenation, which recovers the active center and liberates methanol. Computing the thermodynamic and kinetic parameters of the intermediates and transition states and simulating the reaction pathway with a kinetic Monte Carlo approach, we obtained a turnover frequency of 230 s–1 per active site at 500 K and 50 bar with a 1:9 ratio of CO/H2, exceeding the rate on the empty defect by 3 orders of magnitude and the conventional catalyst by 4 orders of magnitude. The present results indicate that the addition of a metal atom to the alkali halide F center can enhance, stabilize, and control its reactivity. In the case of copper, they point toward the existence of a synthesis route for methanol with an overall activity comparable to the conventional copper-based catalysts but with much smaller metal loading.

Supported Metal Nanohydrides for Hydrogen Storage

Adsorption of hydrogen on graphdiyne (GDY) and boron-graphdiyne (BGDY) doped with palladium clusters has been investigated by performing density functional calculations. Pd6 fits well on the large holes of those porous layers, preserving its octahedral structure in GDY and changing it to a capped trigonal bipyramid structure in BGDY. Pd6GDY adsorbs up to five H2 molecules with sizable adsorption energies, two dissociated and three nondissociated. The dissociation barrier of H2 on the Pd6GDY cluster is 0.58 eV. Pd6BGDY can adsorb up to six molecules, three dissociated and three nondissociated, and the dissociation barrier of H2 on Pd6BGDY is 0.23 eV. In both cases, the dissociation barriers are substantially smaller than the corresponding dissociation barriers on undoped GDY and BGDY. The Pd clusters saturated with hydrogen can be viewed as nanohydrides. Spilling of the adsorbed hydrogen atoms toward the GDY and BGDY substrates is hindered by large activation barriers. We then propose using BGDY and GDY layers as support platforms for metal nanohydrides. The amount of stored hydrogen using Pd as the dopant is below the target of 6% of hydrogen in weight, but replacing Pd by a lighter metal with similar or higher affinity for hydrogen would substantially enhance the storage.