As one of the dominant configurations, platinum (Pt) single atomic catalysts (SACs) have pushed the performance of the hydrogen evolution reaction (HER) to an unprecedented level due to the maximized atomic utilization efficiency of Pt atoms. However, the contribution of atomic clusters, which exist in SACs as well, to the overall catalytic performance is always overlooked, thus limiting further enhancement of the performance of Pt-catalyzed HER. Herein, we report anchoring Pt atomic clusters on N-doped graphene for ultrahigh performance of the HER. Benefiting from optimized electron transfer and larger binding energy between active centers and the substrate, Pt atomic cluster catalysts (ACCs) exhibit higher catalytic activity than their single atomic counterparts after 4000 cycles and more than 16 h for HER in an acid solution. These findings reveal a vast opportunity to enhance the catalytic performance of chemical reactions with noble-metal-based ACCs in the near future.

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Metal atoms often locate in energetically favorite close-packed planes, leading to a relatively high penetration barrier for other atoms. Naturally, the penetration would be much easier through non-close-packed planes, i.e. high-index planes. Hydrogen penetration from surface to the bulk (or reversely) across the packed planes is the key step for hydrogen diffusion, thus influences significantly hydrogen sorption behaviors. In this paper, we report a successful synthesis of Mg films in preferential orientations with both close- and non-close-packed planes, i.e. (0001) and a mix of (0001) and (103), by controlling the magnetron sputtering conditions. Experimental investigations confirmed a remarkable decrease in the hydrogen absorption temperature in the Mg (103), down to 392 K from 592 K of the Mg film (0001), determined by the pressure-composition-isothermal (PCI) measurement. The ab initio calculations reveal that non-close-packed Mg(103) slab is advantageous for hydrogen sorption, attributing to the tilted close-packed-planes in the Mg(103) slab.

CH4 oxidation by an oxygen carrier, such as iron oxide, continues to be involved in many important valuable industrial catalytic processes, including chemical looping combustion. In this paper, reaction pathways of complete and partial oxidations of CH4 on thermodynamically stable hematite (α-Fe2O3) (0001) facets are investigated with periodic GGA + U calculations. Upon Fe–O3–Fe-termination, initial CH4 decomposition proceeds via C–H bond activation on the Fe site, with an energy barrier of 1.04 eV. Subsequent decomposition and oxidation of the CH x species (x = 1, 2, 3) exploit the lattice O species according to the Mars–van Krevelan mechanism, forming CH x O in more thermodynamically and kinetically favorable pathways. The reduced iron oxide can be reoxidized with O2 as the oxidant, allowing VO to greatly facilitate O2 dissociation, i.e., dramatically lowering the O2 dissociation barrier by 2.83 eV, for active site regeneration. Furthermore, CH4 oxidation chemistry involving the ferryl O (i.e., oxygen species adsorbed on the Fe site) is also investigated. The ferryl O species are highly energetic and able to activate the C–H bond via direct oxygen insertion, thereby producing methanol with an energy barrier of 0.37 eV. However, the role of surface ferryl O in iron oxide is limited due to its high reactivity and low concentration indicated by the high surface energy of the O–Fe–O3-terminated surface.

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Metal amides are promising candidates for hydrogen storage, hydrogen production, NH3 synthesis and cracking, and so on. However, the decomposition behaviors and mechanisms of metal amides remain unclear. In this study, the decomposition properties of three metal amides, including LiNH2, Mg­(NH2)2, and NaNH2, are studied by thermogravimetry, mass spectroscopy, and in situ X-ray diffraction techniques combined with density functional theory (DFT) calculations. It is found that Mg­(NH2)2, LiNH2, and NaNH2 exhibit very different metal–N and N–H bond strengths, which precipitate various formations energies of different kinds of vacancies. As a result, LiNH2 releases a major amount of NH3, with a small amount of N2 at a temperature as high as 350 °C. Mg­(NH2)2 releases NH3 and N2 synchronously at a temperature range of 300–400 °C without the emission of H2. NaNH2 synchronously releases H2, NH3, and a small amount of N2, at a narrow temperature range of 275–290 °C. Using DFT calculations, the decomposition behaviors and the corresponding decomposition mechanisms for LiNH2, Mg­(NH2)2, and NaNH2 have been well understood.

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We have studied hydrogen adsorption on the Mg(0001) surface under biaxial strain, using density-functional theory calculations. A phase diagram is obtained for an intuitive sense of how the strain and hydrogen chemical potential affect the structural stabilities of Mg−H system. It is found that the compressive (negative) strains facilitate the formation of the H−Mg−H trilayers, a precursor of the transition to magnesium hydride, due to the fact that the lattice constant of H−Mg−H trilayer is shorter than that of pure Mg. However, the magnesium hydride is more energetically favored with greater lattice constant caused by tensile (positive) strains which exceed +6%. During the hydrogenation, the H−Mg−H trilayer and MgH 2 bulk-like structures could be coexisting, where the strain is able to modulate their relative stabilities. These findings are helpful for the understanding of hydrogenation/ dehydrogenation of the Mg−H system and could ultimately improve the design of Mg-based hydrogen storage materials.