Constructing a interfacial electric field for efficient reduction of nitrogen to ammonia

Electrochemical nitrogen reduction (eNRR) is a cost-effective and environmentally sustainable approach for ammonia production. MoS2, as a typical layered transition metal compound, holds significant potential as an electrocatalyst for the eNRR. Nevertheless, it suffers from a limited number of active sites and low electron transfer efficiency. In this study, we constructed a heterostructure by depositing SnO2 (an n-type semiconductor) nanoparticles on MoS2 (a p-type semiconductor). This unique interfacial structure not only generates abundant interfacial contacts but also facilitates the transfer of electrons from SnO2 to MoS2, leading to the formation of an interfacial electric field. Theoretical calculations demonstrate that this electric field increases the number of active electrons, facilitating N2 adsorption and NN bond activation. Moreover, it increases the degree of orbital overlap between N2 and SnO2/MoS2, effectively reducing the energy barrier of the rate-determining step. Benefiting from the interfacial electric field effect, the SnO2/MoS2 catalyst exhibits significant catalytic activity and selectivity towards eNRR, with an ammonia yield of 47.1 µg h-1 mg-1 and a Faraday efficiency of 19.3 %, surpassing those reported for the majority of MoS2- and SnO2-based catalysts.

Hydrogen Embrittlement as a Conspicuous Material Challenge─Comprehensive Review and Future Directions

Hydrogen is considered a clean and efficient energy carrier crucial for shaping the net-zero future. Large-scale production, transportation, storage, and use of green hydrogen are expected to be undertaken in the coming decades. As the smallest element in the universe, however, hydrogen can adsorb on, diffuse into, and interact with many metallic materials, degrading their mechanical properties. This multifaceted phenomenon is generically categorized as hydrogen embrittlement (HE). HE is one of the most complex material problems that arises as an outcome of the intricate interplay across specific spatial and temporal scales between the mechanical driving force and the material resistance fingerprinted by the microstructures and subsequently weakened by the presence of hydrogen. Based on recent developments in the field as well as our collective understanding, this Review is devoted to treating HE as a whole and providing a constructive and systematic discussion on hydrogen entry, diffusion, trapping, hydrogen-microstructure interaction mechanisms, and consequences of HE in steels, nickel alloys, and aluminum alloys used for energy transport and storage. HE in emerging material systems, such as high entropy alloys and additively manufactured materials, is also discussed. Priority has been particularly given to these less understood aspects. Combining perspectives of materials chemistry, materials science, mechanics, and artificial intelligence, this Review aspires to present a comprehensive and impartial viewpoint on the existing knowledge and conclude with our forecasts of various paths forward meant to fuel the exploration of future research regarding hydrogen-induced material challenges.

Characterization of CO Adsorbed to Clean and Partially Oxidized Cu(211) and Cu(111)

Copper-based catalysts gain activity through the presence of poorly coordinated Cu atoms and incomplete oxidation at the surface. The catalytic mechanisms can in principle be observed by controlled dosing of reactants to single-crystal substrates. However, the interconnected influences of surface defects, partial oxidation, and adsorbate coverage present a large matrix of conditions that have not been fully explored in the literature. We recently characterized oxygen and carbon monoxide coadsorption on Cu(111), a nominally defect-free surface, and now extend our study to the stepped surface Cu(211). Temperature-programmed desorption of CO adsorbed to bare metal surfaces confirms that two sites dominate desorption from a saturated layer: atop terrace atoms of local (111) character and atop step edge atoms with CO bound more strongly to the latter. At low coverage, discrete CO resonances in reflection adsorption infrared spectra can be assigned to these sites: 2077 cm-1 for extended (111) terraces, 2093 cm-1 for step sites, and additional kink-adsorbed molecules at 2110 cm-1. With increasing coverage, in contrast to Cu(111), the infrared spectral features on Cu(211) evolve and shift as a consequence of dipole-dipole coupling between differentially occupied types of sites. Auger electron spectroscopy shows that exposure to background O2 oxidizes the (211) surface at a rate nearly 1 order of magnitude greater than (111); we argue that the resulting surface is stoichiometric Cu2O, as previously found for Cu(111). This oxide binds CO less strongly than the bare metal and the underlying crystal cut continues to influence the adsorption sites available to CO. On oxidized (111) terraces, broad absorption peaks at 2115-2120 cm-1; on oxidized Cu(211), CO adsorbed to step sites appears as a resolved secondary peak at 2144 cm-1. This suite of spectroscopic signatures, obtained under carefully controlled conditions, will help to determine the origin and fate of adsorbed species in future studies of reaction mechanisms on copper.

Crucial impact of exchange between layers on temperature programmed desorption

Desorption of molecules from surfaces constitutes an elementary process that is fundamental in both natural and application-oriented fields, including dewetting, weathering and catalysis. A powerful method to investigate desorption processes is temperature-programmed desorption (TPD), which offers the potential to provide mechanistic insights into the desorption kinetics. Using TPD, the desorption order, the energy barrier as well as the entropy change upon desorption can be accessed. In the past, several analysis methods have been developed for TPD data. These methods have in common that they rely on the Polanyi-Wigner equation, which requires proposing a desorption mechanism with a single (or at least dominating) desorption path. For real systems, however, several coupled desorption paths can be easily envisioned, which cannot be disentangled. Here, we analyse the influence of exchange between the first and the second adsorbate layer on the desorption process. We present a kinetic model, in which molecules can desorb directly from the first layer or change into the second layer and desorb from there. Interestingly, considering this additional desorption pathway alters the desorption spectrum considerably, even if the transient second-layer occupation remains as small as 4 × 10^-6 monolayers. We show that the impact of this layer exchange can be described by a modified Polanyi-Wigner equation. Our study demonstrates that layer exchange can crucially impact the TPD data.

Synthesis of raspberry-like antimony-platinum (SbPt) nanoparticles as highly active electrocatalysts for hydrogen evolution reaction

Binary transition metals can facilitate the hydrogen evolution reaction (HER) through the synergistic integration of different electrochemical properties. To determine binary transition metals that are highly active, Greely et al. conducted a simulation of 256 different binary transition metals. They demonstrated that BiPt, PtRu, AsPt, SbPt, BiRh, RhRe, PtRe, AsRu, IrRu, RhRu, IrRe, and PtRh could be used as efficient electrocatalysts for HER. However, only few of them are synthesized and used as electrocatalysts. In this work, we report the synthesis of the raspberry-like antimony-platinum (SbPt) nanoparticles (NPs) via a colloidal nanocrystal synthesis. These NPs exhibited efficient activity with a low overpotential of 27 mV to reach 10 mA cm^-2 in acidic media. We conducted long-term durability test for 90,000 s under an applied voltage of 0.5 V (vs. RHE) and cycling tests of over 10,000 cycles under an applied voltage of 0.1 to -0.5 V (vs. RHE). The high activity exhibited by the raspberry-like SbPt NPs may be due to the following reasons: (1) the raspberry-like SbPt NPs exhibited versatile active exposed (110), (100), (101), and (012) facets as efficient HER catalysts, and (2) as confirmed by both the density functional theory (DFT) simulation and experimental results, the presence of Sb 3d subsurface broadened the Pt surface d-band, which caused synergistic effects on water splitting. In summary, synthesis of the new colloidal raspberry-like SbPt NPs is essential to elucidate the fundamental properties of the nanomaterial and nanostructure design. This study could facilitate the development of Pt-group materials that can be used as HER catalysts.

Identification of hydrogen species on Pt/Al2O3 by in situ inelastic neutron scattering and their reactivity with ethylene

Active hydrogen species and their dynamics in ethylene hydrogenation reaction were elucidated by in situ INS and DFT calculations.

Monolayered Platinum Nanoparticles as Efficient Electrocatalysts for the Mass Production of Electrolyzed Hydrogen Water

High-performance/low-cost platinum (Pt)-based electrocatalysts have been established by top-coating both sides of a titanium plate with Pt nanoparticles. The average diameter of the Pt nanoparticles used in this study is approximately 100 nm. Three types of Pt top-coated Pt/Ti electrocatalysts, each having different top-coated Pt layer thicknesses, are prepared. Type I is a monolayered Pt top-coated type, in which the thickness of the top-coated Pt layer is approximately 100 nm; Type II is a few-layered type with a top-coated Pt layer thickness of approximately 200 nm, and Type III is a multilayered type with a top-coated Pt layer thickness of approximately 750 nm. The mass loading of Pt is 0.0215 mg cm⁻² for Type I, 0.043 mg cm⁻² for Type II, and 0.161 mg cm⁻² for Type III. The electrocatalytic activities of each type of Pt/Ti electrocatalyst are evaluated through the electrolysis of acidic water and tap water. Type I gives the highest electrocatalytic efficiencies, which are comparable or even better than the electrocatalytic efficiencies of the state-of-the-art commercially available Pt/C electrode and other metal-/carbon-based HER catalysts. For example, in the case of the electrolysis of acidic water at an overpotential of 0.15 V, Type I shows a Tafel slope of 29 mV dec⁻¹ and a current density of 27.5 mA cm⁻². Even in the case of the electrolysis of tap water, Type I gives an HER Faradaic efficiency of 92%. A model of water (H₂O), hydronium ions (H₃O⁺), and hydroxyl ions (OH⁻) properly adsorbing on the Pt (111) facet is proposed to explain the electrocatalytic mechanism. New insights into the distinguishing properties of the resultant electrolyzed hydrogen water (EHW), namely, the healthy beneficial effects of EHW, are also described, and a new concept of storing and carrying reductive hydrogen (H*) by free Pt nanoparticles is proposed.

Precursor chemistry of h-BN: adsorption, desorption, and decomposition of borazine on Pt(110)

Adsorption, desorption and fragmentation of borazine on Pt(110) are studied by temperature-programmed desorption, ultraviolet photoemission spectroscopy, workfunction measurements and density functional theory. Borazine adsorbs in part dissociatively, forming an upright (B₃N₃H₅˙)_ads adsorption complex. Radicals with a N-Pt bond are weakly bound and desorb recombinatively following second-order kinetics. Radicals with a B-Pt bond are similar in binding strength to the molecularly adsorbed species, which binds through dispersive forces to the (111) facets of the (1 × 2) reconstructed Pt(110). Both do not desorb but are dehydrogenated beyond T = 150 K. As T approaches 600 K the B-N ring progressively breaks down into its atomic constituents. The borazine ice multilayer is capable of trapping significant amounts of hydrogen. Previous studies of borazine adsorption on other transition metal surfaces yield a very similar pattern. Reported multiple molecular desorption peaks are artefacts. Implications for the nucleation and growth of h-BN monolayers at high temperatures are discussed.

Elucidation of temperature-programmed desorption of high-coverage hydrogen on Pt(211), Pt(221), Pt(533) and Pt(553) based on density functional theory calculations

In this work we compute high-coverage hydrogen adsorption energies and geometries on the stepped platinum surfaces Pt(211) and Pt(533) which contain a (100)-step type and the Pt(221) and Pt(553) surface with a (111) step edge. We discuss these results in relation to ultra-high-vacuum temperature programmed desorption (TPD) data to elucidate the origin of the desorption features. Our results indicated that on surfaces with a (100)-step type, two distinct ranges of adsorption energy for the step and terrace are observed, which mirrors the TPD spectra for which we find a clear separation of the desorption peaks. For the (111) step type, the TPD spectra show much less separation of the step and terrace features, which we assign to the low individual adsorption energies for H atoms on this step edge. From our results we obtain a much clearer understanding of the surface-hydrogen bonding at high coverages and the origin of the different TPD features present for the two step types studied.

H2 Thermal Desorption Spectra on Pt(111): A Density Functional Theory and Kinetic Monte Carlo Simulation Study

Theoretical investigation of the static and kinetic behaviors of H and H2 on metal surface plays a key role in the development of hydrogenation catalysts and new materials with high H2 storage capacity. Based on the density functional theory (DFT) calculation of H and H2 adsorption on Pt(111), H(a) adatom strongly interacts with surface Pt; while H2 weakly adsorbs on Pt(111). H(a) adatoms stably occupy the face-centered cubic sites on Pt(111) which agrees with the experimental LERS observations. By using kinetic Monte Carlo (kMC) simulation, the qualitative effects of the kinetic parameters on the H2 TDS spectra indicate that the H2 desorption peaks shift to the low temperature with increasing pre-exponential factor and decreasing desorption barrier. Simultaneously, the desorption peaks shift downwards and broaden to two peaks with the increase of the lateral interaction energy among H(a) adatoms. Using the kMC simulation based on DFT calculation, the predicted H2 TDS spectra are well consistent with the experimental ones. It unanimously proves that the two peaks of TDS spectra are derived from the lateral interactions among H(a). This work provides the intrinsic kinetics of H(a) and H2 on Pt(111) at an atomic level, and gives insight into the development of hydrogenation catalysts.

Hydrogen adsorption and desorption from Cu(111) and Cu(211)

We present a combined experimental-theoretical study on structural and coverage dependences of the adsorption and desorption of molecular hydrogen on atomically flat Cu(111) and highly stepped Cu(211) surfaces. For molecules with identical incident energy from supersonic molecular beams, we find a reduced dissociative sticking probability for the stepped surface compared to Cu(111). DFT calculations of activation barriers to dissociation for the clean and partially precovered surfaces, as well as quantitative analysis of TPD spectra, support that the A-type step of the (211) surface causes an upward shift in activation barriers to dissociation and lowering of the desorption barrier. The new data allow us to determine low sticking probabilities at conditions where King and Wells measurements fail to determine the reactivity. They are also fully consistent with the unexpected observation that monoatomic steps on a surface lower the reactivity toward the dissociation of a diatomic molecule.

Nanocatalysts for hydrogen evolution reactions

Hydrogen fuel is among the cleanest renewable resources and is the best alternative to fossil fuels for the future.

Sequential Dihydrogen Desorption from Hydride-Protected Atomically Precise Silver Clusters and the Formation of Naked Clusters in the Gas Phase

We report the formation of naked cluster ions of silver of specific nuclearities, uncontaminated by other cluster ions, derived from monolayer-protected clusters. The hydride and phosphine co-protected cluster, [Ag₁₈(TPP)₁₀H₁₆]²⁺ (TPP, triphenylphosphine), upon activation produces the naked cluster ion, Ag₁₇⁺, exclusively. The number of metal atoms present in the naked cluster is almost the same as that in the parent material. Two more naked cluster ions, Ag₂₁⁺ and Ag₁₉⁺, were also formed starting from two other protected clusters, [Ag₂₅(DPPE)₈H₂₂]³⁺ and [Ag₂₂(DPPE)₈H₁₉]³⁺, respectively (DPPE, 1,2-bis(diphenylphosphino)ethane). By systematic fragmentation, naked clusters of varying nuclei are produced from Ag₁₇⁺ to Ag₁⁺ selectively, with systematic absence of Ag₁₀⁺, Ag₆⁺, and Ag₄⁺. A seemingly odd number of cluster ions are preferred due to the stability of the closed electronic shells. Sequential desorption of dihydrogen occurs from the cluster ion, Ag₁₇H₁₄⁺, during the formation of Ag_n⁺. A comparison of the pathways in the formation of similar naked cluster ions starting from two differently ligated clusters has been presented. This approach developed bridges the usually distinct fields of gas-phase metal cluster chemistry and solution-phase metal cluster chemistry. We hope that our findings will enrich nanoscience and nanotechnology beyond the field of clusters.

The dissociation and recombination rates of CH4 through the Ni(111) surface: The effect of lattice motion

Methane dissociation is a prototypical system for the study of surface reaction dynamics. The dissociation and recombination rates of CH₄ through the Ni(111) surface are calculated by using the quantum instanton method with an analytical potential energy surface. The Ni(111) lattice is treated rigidly, classically, and quantum mechanically so as to reveal the effect of lattice motion. The results demonstrate that it is the lateral displacements rather than the upward and downward movements of the surface nickel atoms that affect the rates a lot. Compared with the rigid lattice, the classical relaxation of the lattice can increase the rates by lowering the free energy barriers. For instance, at 300 K, the dissociation and recombination rates with the classical lattice exceed the ones with the rigid lattice by 6 and 10 orders of magnitude, respectively. Compared with the classical lattice, the quantum delocalization rather than the zero-point energy of the Ni atoms further enhances the rates by widening the reaction path. For instance, the dissociation rate with the quantum lattice is about 10 times larger than that with the classical lattice at 300 K. On the rigid lattice, due to the zero-point energy difference between CH₄ and CD₄, the kinetic isotope effects are larger than 1 for the dissociation process, while they are smaller than 1 for the recombination process. The increasing kinetic isotope effect with decreasing temperature demonstrates that the quantum tunneling effect is remarkable for the dissociation process.

Stabilization of volatile Ti(BH4)3 by nano-confinement in a metal-organic framework

Volatile Ti(BH₄)₃ molecules stabilized on the surface of a MOF.

Liquid complex hydrides are a new class of hydrogen storage materials with several advantages over solid hydrides, e.g. they are flexible in shape, they are a flowing fluid and their convective properties facilitate heat transport. The physical and chemical properties of a gaseous hydride change when the molecules are adsorbed on a material with a large specific surface area, due to the interaction of the adsorbate with the surface of the host material and the reduced number of collisions between the hydride molecules. In this paper we report the synthesis and stabilization of gaseous Ti(BH₄)₃. The compound was successfully stabilized through adsorption in nanocavities. Ti(BH₄)₃, upon synthesis in its pure form, spontaneously and rapidly decomposes into diborane and titanium hydride at room temperature in an inert gas, e.g. argon. Ti(BH₄)₃ adsorbed in the cavities of a metal organic framework is stable for several months at ambient temperature and remains stable up to 350 K under vacuum. The adsorbed Ti(BH₄)₃ reaches approximately twice the density of the gas phase. The specific surface area (BET, N₂ adsorption) of the MOF decreased from 1200 m² g^–1 to 770 m² g^–1 upon Ti(BH₄)₃ adsorption.

Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed.

Density functional theory study of adsorption of H2O, H, O, and OH on stepped platinum surfaces

We report on density functional theory (DFT)-GGA (generalized gradient approximation) computed adsorption energetics of water and the water-related fragments OH, O, and H on stepped Pt surfaces in the low coverage limit. The Pt(100) step edge as encountered on Pt(533) shows increased binding for all species studied, while the Pt(110) step edge, as found on Pt(553) shows only significantly enhanced binding for O and OH. Comparing these results to ultra high vacuum experiments reveals that DFT can explain the main experimental trends semiquantitatively.