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Transition metal nitrides are a fascinating class of catalyst materials due to their superior catalytic activity, low electrical resistance, good corrosion resistance and earth abundance; however, their conventional synthesis relies on high-temperature nitridation processes in hazardous environments. Here, we report a direct synthesis of Ni3N/Ni enriched with N-vacancies using one-step magnetron sputtering. The surface state of Ni3N(001) with 75% N-vacancies is hydrogen-terminated and exhibits four inequivalent Ni3-hollow sites. This leads to stronger H* binding compared to Ni(111), and is affirmed as the most stable surface termination under the electrochemical working conditions (pH ≈ 13.8 and E = −0.1 V) from the Pourbaix diagram. The Ni3N/Ni catalyst shows low crystallinity and good wettability and exhibits a low overpotential of 89 mV vs. RHE at 10 mA cm−2 in 1.0 M KOH with excellent stability over 3 days. This performance closely matches that of the Pt catalyst synthesized under the same conditions and surpasses that of other reported earth-abundant catalysts on planar substrates. The application of Ni3N/Ni as a cocatalyst on Si photocathodes produces an excellent ABPE of 9.3% and over 50 h stability. Moreover, its feasibility for practical application was confirmed with excellent performance on porous substrates and robustness at high operating currents in zero-gap alkaline electrolysis cells. Our work demonstrates a general approach for the feasible synthesis of other transition metal nitride catalysts for electrochemical and photoelectrochemical energy conversion applications.

Tantalum cluster cations react with CO2 either via transfer of oxygen atoms to the clusters or the adsorption of an entire molecule. The released energy and vibrational heat capacities are assigned to determine the branching ratios of the pathways.

The molecular reorganization energy $\lambda$ strongly influences the charge carrier mobility of organic semiconductors and is therefore an important target for molecular design. Machine learning (ML) models generally have the potential to strongly accelerate this design process (e.g. in virtual screening studies) by providing fast and accurate estimates of molecular properties. While such models are well established for simple properties (e.g. the atomization energy), $\lambda$ poses a significant challenge in this context. In this paper, we address the questions of how ML models for $\lambda$ can be improved and what their benefit is in high-throughput virtual screening (HTVS) studies. We find that, while improved predictive accuracy can be obtained relative to a semiempirical baseline model, the improvement in molecular discovery is somewhat marginal. In particular, the ML enhanced screenings are more effective in identifying promising candidates but lead to a less diverse sample. We further use substructure analysis to derive a general design rule for organic molecules with low $\lambda$ from the HTVS results.

The deeper reduction of CO to multi-carbon-based fuels with higher energy densities and wider applicability has recently triggered extensive experimental and theoretical research. However, present-day catalysts for the generation of multi-carbon products (C2+) suffer from ultra-high energy barrier for C-C bond formation and poor selectivity, which poses great challenges for practical application. Herein, we propose and evidence with first-principles calculations a novel catalyst for the conversion of CO into more value-added ethylene and ethanol under visible light, consisting of active Cu-B atomic pair decorated graphitic carbon nitride (Cu-B@g-C3N4). Our results show that the low coordinated Cu-B atomic pair anchored on g-C3N4 could effectively reduce the CO dimerization free energy barrier to a record value of 0.63 eV. This high catalytic performance stems from the moderate binding strength of the intermediates modulated by the asymmetric synergy of the atomically dispersed metal Cu and non-metal B that can break the linear scaling relationship of traditional transitional metal catalysts. Moreover, the low-coordinated Cu-B active site with synergistic d-p coupling can significantly suppress the parasitic hydrogen evolution reaction. Compared to pure g-C3N4, the Cu-B@g-C3N4 catalyst also becomes more optically active under visible and even infrared light. Ab initio molecular dynamics simulations suggest that the Cu-B@g-C3N4 catalyst possesses a high thermal stability. Considering that efficient catalysts for C2+ production are currently essentially limited to Cu-bimetallic systems, our work highlights a fully new concept towards the development of novel CO reduction catalysts based on synergistic coupling between metal Cu and non-metal atoms.

Even though the surface-assisted dehalogenative coupling constitutes the most abundant protocol in on-surface synthesis, its full potential will only become visible if selectivity issues with polybrominated precursors are comprehensively understood, opening new venues for both organometallic self-assembly and on-surface polymerization. Using the 3,3',5,5'-tetrabromo-2,2',4,4',6,6'-hexafluorobiphenyl (Br4F6BP) at Ag(111), we demonstrate a remote site-selective functionalization at room temperature and a marked temperature difference in double- vs. quadruple activation, both phenomena caused by conformational mechanical effects of the precursor-surface ensemble. The submolecularly resolved structural characterization was achieved by Scanning Tunneling Microscopy, the chemical state was quantitatively assessed by X-ray Photoelectron Spectroscopy, and the analysis of the experimental signatures was supported through first-principles Density-Functional Theory calculations. The non-planarity of the various structures at the surface was specifically probed by additional Near Edge X-ray Absorption Fine Structure experiments. Upon progressive heating, Br4F6BP on Ag(111) shows the following unprecedented phenomena: (1) formation of regular organometallic 1D chains via remote site-selective 3,5'-didebromination; (2) a marked temperature difference in double- vs. quadruple activation; (3) an organometallic self-assembly based on reversibility of C-Ag-C linkages with a thus far unknown polymorphism affording both hexagonal and rectangular 2D networks; (4) extraordinary thermal stability of the organometallic networks. Controlled covalent coupling at the previously Br-functionalized sites was not achieved for the Br4F6BP precursor, in contrast to the comparatively studied non-fluorinated analogue.

The reaction of small cationic tantalum clusters (Tan+, n = 4-8) with molecular oxygen is studied under multi-collision conditions in the gas phase, and the reaction kinetics are analyzed in order to elucidate underlying mechanisms. Reaction pathways as well as relevant apparent rate constants are reported. Two principal pathways in the consecutive oxidation reaction are present in this size regime: solely oxidative degradation (loss of a TaO fragment) in the beginning followed by parallel intact oxidation of certain intermediate species. Selected product structures and energies are subsequently determined via density functional theory calculations. The branching between oxidative fragmentation and intact oxidation is related to the corresponding relaxation dynamics.

Density functional theory is used to examine the changes in electronic structure that occur during the oxygen evolution reaction (OER) catalyzed by active sites on three different surface terminations of Co3O4. These three active sites have reactive oxo species with differing degrees of coordination by Co cations - a \textgreek{m}(3)-oxo on the (311) surface, a \textgreek{m}(2)-oxo on the (110)-A surface, and an \textgreek{h}-oxo on the (110)-B surface. The kinetically relevant step on all surfaces over a wide range of applied potentials is the nucleophilic addition of water to the oxo, which is responsible for formation of the O-O bond. The intrinsic reactivity of a site for this step is found to increase as the coordination of the oxo decreases with the \textgreek{m}(3)-oxo on the (311) surface being the least reactive and the \textgreek{h}-oxo on the (110)-B surface being the most reactive. A detailed analysis of the electronic changes occurring during water addition on the three sites reveals that this trend is due to both a decrease in the attractive local Madelung potential on the oxo and a decrease in electron withdrawal from the oxo by Co neighbors. Applying a similar electronic structure analysis to the oxidation steps preceding water addition in the catalytic cycle shows that analogous electronic changes occur during this process, explaining a correlation observed between the oxidation potential of a site and its intrinsic reactivity for water addition. This concept is then used to specify criteria for the design of an optimal OER catalyst at a given applied potential.

Lithium zirconate (LZO) is a prototype material for studies of Li+ ion mobility with a wide range of possible applications such as a ceramic breeder for nuclear reactors, a reversible sorbent for carbon dioxide capture, a coating for cathodes and anodes or even directly as an anode material in lithium-ion batteries (LIBs). Solid state nuclear magnetic resonance (NMR) is a powerful experimental technique with the potential to provide microscopic insights into Li+ ion dynamics in solid materials, in particular if combined with theory to interpret the measured spectra. We use first-principles atomistic simulations based on density functional theory (DFT) to investigate the Li+ ion migration mechanisms in LZO. Computed barrier heights for several possible Li+ ion exchange pathways are in very good agreement with the experimentally reported values and confirm the relevance of lithium vacancies for the observed Li+ ion mobilities. Additionally, 7Li NMR isotropic spectral parameters such as quadrupolar coupling constants and chemical shifts, can be obtained by the gauge-including projector-augmented-wave (GIPAW) method in very good agreement with the experimental values, underpinning the validity of the computational models. The close analysis of these spectral parameters shows a clear correlation to simple descriptors for the local structural environment of the Li+ ions, opening up a pathway to further modelling based on computationally cheaper methods. We note, however, that there is also a consistently poor agreement with experimental data for 7Li anisotropic properties like the asymmetry parameter of the electric field gradient (EFG) tensor, which calls for further theoretical method development in this field.

Carbon Capture and Sequestration (CCS) is one of the promising ways to significantly reduce the CO2 emission from power plants. In particular, amongst several separation strategies, adsorption by nano-porous materials is regarded as a potential means to efficiently capture CO2 at the place of its origin in a post-combustion process. The search for promising materials in such a process not only requires the screening of a multitude of materials but also the development of an adequate evaluation metric. Several evaluation criteria have been introduced in the literature concentrating on a single adsorption or material property at a time. Parasitic energy is a new approach for material evaluation to address the energy load imposed on a power plant while applying CCS. In this work, we evaluate over 60 different materials with respect to their parasitic energy, including experimentally realized and hypothetical materials such as metal–organic frameworks (MOFs), zeolitic imidazolate frameworks (ZIFs), porous polymer networks (PPNs), and zeolites. The results are compared to other proposed evaluation criteria and performance differences are studied regarding the regeneration modes, (i.e. Pressure-Swing (PSA) and Temperature-Swing Adsorption (TSA)) as well as the flue gas composition.

The adsorption geometry of 1,3,5-tris(4-mercaptophenyl)benzene (TMB) on Cu(111) is determined with high precision using two independent methods, experimentally by quantitative low energy electron diffraction (LEED-I(V)) and theoretically by dispersion corrected density functional theory (DFT-vdW). Structural refinement using both methods consistently results in similar adsorption sites and geometries. Thereby a level of confidence is reached that allows deduction of subtle structural details such as molecular deformations or relaxations of copper substrate atoms., 7 pages, 3 figures