Hydrogen embrittlement in metals has posed a serious obstacle to designing strong and reliable structural materials for many decades, and predictive physical mechanisms still do not exist. Here, a new H embrittlement mechanism operating at the atomic scale in α-iron is demonstrated. Direct molecular dynamics simulations reveal a ductile-to-brittle transition caused by the suppression of dislocation emission at the crack tip due to aggregation of H, which then permits brittle-cleavage failure followed by slow crack growth. The atomistic embrittlement mechanism is then connected to material states and loading conditions through a kinetic model for H delivery to the crack-tip region. Parameter-free predictions of embrittlement thresholds in Fe-based steels over a range of H concentrations, mechanical loading rates and H diffusion rates are found to be in excellent agreement with experiments. This work provides a mechanistic, predictive framework for interpreting experiments, designing structural components and guiding the design of embrittlement-resistant materials.

We have investigated the phase transformation of bulk MoS2 crystals from the metastable metallic 1T/1T' phase to the thermodynamically stable semiconducting 2H phase. The metastable 1T/1T' material was prepared by Li intercalation and deintercalation. The thermally driven kinetics of the phase transformation were studied with in situ Raman and optical reflection spectroscopies and yield an activation energy of 400 ± 60 meV (38 ± 6 kJ/mol). We calculate the expected minimum energy pathways for these transformations using DFT methods. The experimental activation energy corresponds approximately to the theoretical barrier for a single formula unit, suggesting that nucleation of the phase transformation is quite local. We also report that femtosecond laser writing converts 1T/1T' to 2H in a single laser pass. The mechanisms for the phase transformation are discussed.

Photoelectrochemical (PEC) reduction of CO with HO not only provides an opportunity for reducing net CO emissions but also produces value-added chemical feedstocks and fuels. Syngas, a mixture of CO and H, is a key feedstock for the production of methanol and other commodity hydrocarbons in industry. However, it is challenging to achieve efficient and stable PEC CO reduction into syngas with controlled composition owing to the difficulties associated with the chemical inertness of CO and complex reaction network of CO conversion. Herein, by employing a metal/oxide interface to spontaneously activate CO molecule and stabilize the key reaction intermediates, we report a benchmarking solar-to-syngas efficiency of 0.87% and a high turnover number of 24 800, as well as a desirable high stability of 10 h. Moreover, the CO/H ratios in the composition can be tuned in a wide range between 4:1 and 1:6 with a total unity Faradaic efficiency. On the basis of experimental measurements and theoretical calculations, we present that the metal/oxide interface provides multifunctional catalytic sites with complementary chemical properties for CO activation and conversion, leading to a unique pathway that is inaccessible with the individual components. The present approach opens new opportunities to rationally develop high-performance PEC systems for selective CO reduction into valuable carbon-based chemicals and fuels.

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The electrochemical reduction of N 2 to NH 3 is emerging as ap romising alternative for sustainable and distributed production of NH 3 .H owever,t he development has been impeded by difficulties in N 2 adsorption, protonation of *NN,a nd inhibition of competing hydrogen evolution. To address the issues,w ed esign ac atalyst with diatomic Pd-Cu sites on N-doped carbon by modulation of single-atom Pd sites with Cu. The introduction of Cu not only shifts the partial density of states of Pd toward the Fermi level but also promotes the d-2p*c oupling between Pd and adsorbed N 2 ,l eading to enhanced chemisorption and activated protonation of N 2 ,and suppressed hydrogen evolution. As ar esult, the catalyst achieves ah igh Faradaic efficiency of 24.8 AE 0.8 %a nd ad esirable NH 3 yield rate of 69.2 AE 2.5 mgh À1 mg cat. À1 ,f ar outperforming the individual single-atom Pd catalyst. This work paves ap athway of engineering single-atom-based electrocatalysts for enhanced ammonia electrosynthesis.

An Si photoelectrode with a nanoporous Au thin film for highly selective and efficient photoelectrochemical (PEC) CO 2 reduction reaction (CO 2 RR) is presented. The nanoporous Au thin film is formed by electrochemical reduction of an anodized Au thin film. The electrochemical treatments of the Au thin film critically improve CO 2 reduction catalytic activity of Au catalysts and exhibit CO Faradaic efficiency of 96% at 480 mV of overpotential. To apply the electrochemical pretreatment of Au films for PEC CO 2 RR, a new Si photoelectrode design with mesh-type co-catalysts independently wired at the front and the back of the photoelectrode is demonstrated. Due to the superior CO 2 RR activity of the nanoporous Au mesh and high photovoltage from Si, the Si photoelectrode with the nanoporous Au thin film mesh shows conversion of CO 2 to CO with 91% Faradaic efficiency at positive potential than the CO 2 / CO equilibrium potential.

Development of efficient and selective electrocatalysts is a key challenge to achieve an industry-relevant electrochemical CO 2 reduction reaction (CO 2 RR) to produce commodity chemicals. Here, we report that Au 25 clusters with Authiolate staple motifs can initiate electrocatalytic reduction of CO 2 to CO with nearly zero energy loss and achieve a high CO 2 RR current density of 540 mA cm −2 in a gas-phase reactor. Electrochemical kinetic investigations revealed that the high CO 2 RR activity of the Au 25 originates from the strong CO 2 binding affinity, leading to high CO 2 electrolysis performance in both concentrated and dilute CO 2 streams. Finally, we demonstrated an 18.0% solar-to-CO conversion efficiency using a Au 25 electrolyzer powered by a Ga 0.5 In 0.5 P/GaAs photovoltaic cell. The electrolyzer also showed 15.9% efficiency and a 5.2% solar-driven single-path CO 2 conversion rate in a 10% CO 2 gas stream, the CO 2 concentration in a typical flue gas.

Anion exchange membrane fuel cells are limited by the slow kinetics of alkaline hydrogen oxidation reaction (HOR). Here, we establish HOR catalytic activities of single-atom and diatomic sites as a function of *H and *OH binding energies to screen the optimal active sites for the HOR. As a result, the Ru-Ni diatomic one is identified as the best active center. Guided by the theoretical finding, we subsequently synthesize a catalyst with Ru-Ni diatomic sites supported on N-doped porous carbon, which exhibits excellent catalytic activity, CO tolerance, and stability for alkaline HOR and is also superior to single-site counterparts. In situ scanning electrochemical microscopy study validates the HOR activity resulting from the Ru-Ni diatomic sites. Furthermore, in situ x-ray absorption spectroscopy and computational studies unveil a synergistic interaction between Ru and Ni to promote the molecular H 2 dissociation and strengthen OH adsorption at the diatomic sites, and thus enhance the kinetics of HOR.