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Two-dimensional (2D) materials are presently being extensively studied in photo(electro)catalysis due to their excellent light absorption, high specific surface area, and readily tunable electronic properties. Electronic structure calculations are of great importance for improving our understanding of the activities of 2D materials. In this work, we perform density functional theory based molecular dynamics (DFTMD) simulations to simulate the explicit 2D material–water interfaces and study the water effects on band gaps and band edge positions in detail. Nine 2D materials with three kinds of typical surface structures are considered, including BN, MoS2, WS2, Black-P, GaSe, GaTe, CrCl3, MoO3, and V2O5. We find that the band gap will decrease when interacting with water, which is induced by a combination of structural and electronic effects. Especially, overlaps between electron densities of solid surfaces and liquid water molecules may change the band gap significantly. The band edge shifts are mainly determined by the net orientation of water molecules at the interfaces. More importantly, our results show that water dipoles are related to surface structures and may not be negligible. Our findings emphasize the water effects on electronic structures and pave the way to screen low-cost and high-efficiency 2D material photocatalysts.

The perovskite LaCoO3exhibits an electrochemical activation process during hydrogen evolution reaction (HER) measurement. In-situ generated oxygen vacancies (Vo) optimize the hydrogen adsorption and water dissociation and thereby promote a high activity for HER.

The electrocatalytic C–N coupling for one-step urea synthesis under ambient conditions serves as the promising alternative to the traditional urea synthetic protocol. However, the hydrogenation of intermediate species hinders the efficient urea synthesis. Herein, the oxygen vacancy-enriched CeO2was demonstrated as the efficient electrocatalyst with the stabilization of the crucial intermediate of *NO viainserting into vacant sites, which is conducive to the subsequent C–N coupling process rather than protonation, whereas the poor selectivity of C–N coupling with protonation was observed on the vacancy-deficient catalyst. The oxygen vacancy-mediated selective C–N coupling was distinguished and validated by the in situsum frequency generation spectroscopy. The introduction of oxygen vacancies tailors the common catalyst carrier into an efficient electrocatalyst with a high urea yield rate of 943.6 mg h–1g–1, superior than that of partial noble-metal-based electrocatalysts. This work provides novel insights into the catalyst design and developments of coupling systems.

The space nuclear reactor cooled by heat pipes has become the preferred choice for future space missions and deep space exploration missions. The use of low-enriched uranium (LEU) is promoted to achieve the goal of nuclear non-proliferation worldwide. In this study, a lithium heat pipe cooled space reactor with LEU (HP-LEU) was proposed based on Heat Pipes-Segmented Thermoelectric Module Converters (HP-STMCs), with the addition of moderators. The HP-LEU employs yttrium hydride (YH2) as the moderator and 19.9 % enriched uranium nitride (UN) as the fuel. The neutronics analysis has been performed on the HP-LEU reactor and the results have showed that the HP-LEU has a lifetime of more than 12 years. Two control systems have been applied in the reactor and have demonstrated the capacity to independently regulate and shut down the reactor. The total temperature reactivity coefficients are consistently negative, indicating that the HP-LEU reactor is inherently safe during operation. During normal operation, the temperatures of the materials are all acceptable. This study can serve as a reference for lithium heat pipe cooled space reactors with LEU.

The use of nitrogen fertilizers has been estimated to have supported 27% of the world’s population over the past century. Urea (CO(NH2)2) is conventionally synthesized through two consecutive industrial processes, N2+ H2→ NH3followed by NH3+ CO2→ urea. Both reactions operate under harsh conditions and consume more than 2% of the world’s energy. Urea synthesis consumes approximately 80% of the NH3produced globally. Here we directly coupled N2and CO2in H2O to produce urea under ambient conditions. The process was carried out using an electrocatalyst consisting of PdCu alloy nanoparticles on TiO2nanosheets. This coupling reaction occurs through the formation of C–N bonds via the thermodynamically spontaneous reaction between *N=N* and CO. Products were identified and quantified using isotope labelling and the mechanism investigated using isotope-labelled operando synchrotron-radiation Fourier transform infrared spectroscopy. A high rate of urea formation of 3.36 mmol g–1h–1and corresponding Faradic efficiency of 8.92% were measured at –0.4 V versus reversible hydrogen electrode.

Transition metal oxides are being actively pursued as low-cost electrocatalysts for the oxygen evolution reaction (OER) in many electrochemical energy devices. A fundamental understanding of the oxide electronic structures, along with the ability to rationally tune them, is a key step toward designing of highly active catalysts. Here, we report the tuning of the electronic structure of NiO via Li doping (LixNi1–xO) to enhance the OER activities. We identified that Li0.5Ni0.5O (LiNiO2) has the highest OER activity, comparable to or exceeding that of the benchmark perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δand LaNiO3. More importantly, a synergistic combination of synchrotron-based photoemission spectroscopy, X-ray absorption spectroscopy, and density functional theory was used to unravel the electronic structure of LixNi1–xO with unprecedented accuracy, thus providing deep insight into the origin of the enhanced catalytic activity. The results unambiguously reveal the creation of a new hole state at 1.1 eV above the Fermi level and an enhanced degree of O 2p–Ni 3d hybridization induced by Li doping optimize the adsorption energetics of OH intermediates and thereby facilitate the fast kinetics for the OER. The LixNi1–xO would serve as a new platform to study the relationship of composition–electronic structure–activity for OER electrocatalysts, beyond the extensively studied Co-based perovskites.

ABSTRACTDuring a severe accident in a pressurized water reactor, large quantities of hydrogen can be produced and released into the containment. The hydrogen mixed with air may be ignited. Rapid pressure rise is likely to occur during hydrogen combustion in a semi-confined compartment because the length–diameter ratio of the compartment is relatively large and there generally are some devices and components in the compartment. Obstacle position and number have a significant and complex effect on combustion pressure. In this paper, a numerical analysis of the effects of obstacle position and number on the overpressure of hydrogen combustion in a semi-confined compartment was carried out to identify the arrangement of obstacles that can decrease the pressure loads generated by hydrogen combustion. The overpressure in the compartment with a single obstacle was found first increases to a maximum value and then decreases as the obstacle moving from the closed end to the open end. When there are multiple obstacles existing in the compartment, minimize the obstacle spacing and number is likely to reduce the maximum overpressure of hydrogen combustion. In addition, intentionally adjust the length of obstacle array may help for reducing the maximum overpressure.

Pd- or Pt-based precious catalysts (PPC) are considered to be the best candidates toward high performance directly ethanol fuel cells (DEFC) applications, owing to their high intrinsic activity for ethanol oxidation reaction (EOR). However, the current major barrier for their commercialization is incompletely oxidized intermediates (IOI, such as CO) that poison the catalysts to affect the durability of the cells. Meanwhile, deactivated PPC catalyst is difficult to be recycled, thus impairing the economic benefits for the commercial applications. Moreover, because of the side effects of additive corrosion and aging, the carbon and organic binders widely used in current catalyst design would make the interactions of the IOI more complex to accelerate activity loss. Here, we report a Pd/amorphous SrRuO3(Pd/a-SrRuO3) hybrid film as a promising material to overcome these problems. Perovskite SrRuO3can effectively generate oxygen-contains (*OH, *OOH) for intermediates oxidation, providing an ideal platform to promote self-cleaning of CO on Pd activity sites. On the other hand, in analogy to typical self-adapting effect of amorphous catalyst in oxygen reduction reaction process, metastable state of amorphous SrRuO3in this work is expected to prolong the activity adaptation region at the initial stage of cycling. Furthermore, our conceptual framework of directly depositing Pd/a-SrRuO3film on operational electrode provides an effective solution to avoid the side effects related with carbon and binders, leading to superior reactivation phenomena with 98% efficiency. As a result, our designed Pd/a-SrRuO3hybrid film exhibits superior EOR activity (4.0 A mg-1 Pd), durability (i-t, 60,000s), self-adapting region (exceeding 400 cycles with ending activity of 3.0 A mg-1 Pd at 1000th cycle), and also a long-term operation (CP) up to 300,000s with 10 times reactivation. This demonstration of a Pd/Pt-based hybrid catalyst with dual-capability of self-cleaning and self-adapting characteristics is an important step towards the development of highly durable EOR catalysts, with an enormous potential to promote practical application of DEFC.