Sodalite-like carbon based superconductors with Tc about 77 K at ambient pressure

The attainment of superconductivity at room temperature is a longstanding aspiration for both experimental and theoretical scientists. Materials exhibiting superconductivity under ambient conditions would have significant applications. Here, we report two metastable phases of sodalite-like carbon based superconductors, GaC6 and GeC6, at ambient pressure using the CALYPSO structural search method and first-principles calculations. Our calculations reveal that both GaC6 and GeC6 compounds have Im[3 with combining macron]m symmetry and are dynamically stable at ambient pressure with Tc values up to the boiling point of liquid nitrogen. The underlying mechanisms indicate that the guest Ga and Ge atoms play a dual role in enhancing the structural stability and concurrently acting as electron donors, thereby modulating the electronic properties of the C24 covalent frameworks, i.e. from insulating states to superconducting states. The present results offer insights into the exploration of novel high temperature superconductors under ambient conditions

Boosting oxygen evolution over inverse spinel Fe-Co-Mn oxide nanocubes through electronic structure engineering

Fossil fuels are urgent to be replaced with renewable energies to achieve carbon neutrality. Intermittent renewable energies such as solar and wind could be stored in chemical bonds, such as hydrogen and carbon-containing chemicals through water and CO2 electrolyzers respectively. Those two energy systems share a common anodic reaction, the sluggish oxygen evolution reaction (OER), which currently relies on precious noble metals to achieve a reasonable energy conversion efficiency. Herein, tuning the d-band center of Fe-based inverse spinel oxides has been achieved through compositions and morphologies engineering. Ternary Mn0.5Co0.5Fe2O4 nanocubes exhibit oxygen evolution activity superior to the benchmark RuO2. Mössbauer and in-situ infrared spectra combined with density functional theory calculations prove that the optimized d-band center offers a balanced adsorption strength of intermediate *OOH on Mn0.5Co0.5Fe2O4 nanocubes. This work provides a promising approach to the design and synthesis of highly efficient electrocatalysts beyond oxygen evolution.</p

Surface Structure Enhanced Microchannel Flow Boiling

We investigated the role of surface microstructures in two-phase microchannels on suppressing flow instabilities and enhancing heat transfer. We designed and fabricated microchannels with well-defined silicon micropillar arrays on the bottom heated microchannel wall to promote capillary flow for thin film evaporation while facilitating nucleation only from the sidewalls. Our experimental results show significantly reduced temperature and pressure drop fluctuation especially at high heat fluxes. A critical heat flux (CHF) of 969 W/cm2 was achieved with a structured surface, a 57% enhancement compared to a smooth surface. We explain the experimental trends for the CHF enhancement with a liquid wicking model. The results suggest that capillary flow can be maximized to enhance heat transfer via optimizing the microstructure geometry for the development of high performance two-phase microchannel heat sinks.United States. Office of Naval Research (N00014-15-1-2483)Masdar Institute of Science & Technology - MIT Technology & Development Program (Cooperative agreement, Reference 02/MI/MI/CP/11/07633/GEN/G/00)United States. Air Force Office of Scientific ResearchBattelle Memorial InstituteSingapore-MIT Alliance for Research and Technology (SMART

Impact of Cereal Production Displacement from Urban Expansion on Ecosystem Service Values in China: Based on Three Cropland Supplement Strategies

The acceleration of global urban expansion constantly occupies high-quality cropland and affects regional food security. The implementation of cropland protection policies has alleviated the pressure of cropland loss worldwide, and thus keeping a dynamic balance of cereal production. Such a displacement of cereal production from the lost cropland to the supplemented cropland has resulted in the massive losses of natural habitats (such as forests, grasslands, and wetlands) as well as ecosystem service values. However, the impact of cereal production displacement caused by different cropland supplement strategies has not been concerned. Therefore, taking China (mainland) as a case, this study used the LANDSCAPE model to simulate cereal production displacement caused by urban expansion and cropland supplement between 2020 and 2040, based on three scales of the Chinese administration system (i.e., the national level, the provincial level, and the municipal level). The natural habitat loss and corresponding ecosystem service value (ESV) loss were assessed. The results show that the national-scale cereal displacement will lead to a large reclamation of cropland in North China, causing the most natural habitat loss (5090 km2), and the least ESV loss (46.53 billion yuan). Cereal production displacement at the provincial and municipal scales will lead to fewer natural habitat losses (4696 km2 and 4954 km2, respectively), but more ESV losses (54.16 billion yuan and 54.02 billion yuan, respectively). Based on the national food security and ecological conservation in China, this study discussed the reasons for the ecological effects of cereal production displacement, direct and indirect natural habitat loss of urban expansion, and cropland protection policies in China. We suggest that China&rsquo;s cropland protection policy should emphasize avoiding large-scale cropland displacement and occupation of natural habitat with high ESV for cropland supplement

Highly efficient CO2electrolysis within a wide operation window using octahedral tin oxide single crystals

Electrocatalytic CO2reduction is an effective way to close the global carbon cycle. Tin oxides have been demonstrated as promising catalysts to convert CO2into formate with high selectivity but with low reactivity and within a narrow potential window. Herein, octahedral tin oxide (SnO2) single crystals have been well tuned and exhibited a high formate selectivity within a 500 mV wide operation range and a remarkable high formate partial current density of ∼500 mA cm−2.In situRaman spectroscopy and DFT calculations indicate that high-energy facets of SnO2favor the adsorption of *OCHO and the desorption of HCOOH*, which breaks the limitation of the scaling relationship of these intermediates on the (110) facet of conventional SnO2nanoparticles and thus enhances formate selectivity. More interestingly, a maximum formate selectivity of 95% is achieved on SnO2(111) due to the deeply suppressed hydrogen evolution in seawater. These catalysts have been further coupled with chlor-alkali electrolyzers to convert greenhouse gas CO2into formate and produce higher-value Cl2simultaneously. The present work will advance the development of practical CO2electrolyzers

Stable Surface-Anchored Cu Nanocubes for CO2Electroreduction to Ethylene

The electrochemical carbon dioxide reduction reaction (CO2RR) is a promising solution to the current environmental and energy issues. Cu is the only metal catalyst able to convert CO2 into high-value-added hydrocarbons. However, Cu catalysts tend to degrade with the decrease in the hydrocarbon selectivity under operation conditions. Herein, we monitored the morphological evolution of Cu nanocatalysts and correlated with changes in the selectivity of hydrocarbon products during electrochemical CO2 reduction. Initial Cu nanospheres quickly reconstructed into nanocubes within 1 h of CO2 electrolysis and then gradually turned into even smaller irregular nanoparticles. Interestingly, the above unstable Cu nanocube offered the maximum ethylene selectivity. We successfully stabilized these Cu nanocubes using a 2D graphene surface doped with nitrogen to achieve high ethylene selectivity over 24 h. Our X-ray photoelectron spectroscopy (XPS) and density-functional theory (DFT) investigations show that the strong interaction between Cu and pyridinic nitrogen on the 2D graphene surface plays a key role in stabilizing Cu nanocubes

Asymmetrical electro-hydrogenation of CO2 to ethanol with Copper-Gold heterojunctions

Copper is distinctive in electrocatalyzing reduction of CO2 into various energy-dense forms, but it often suffers from limited product selectivity including ethanol in competi-tion with ethylene. Here, we describe systematically designed, bimetallic electrocatalysts based on copper/gold heterojunctions with a faradaic efficiency toward ethanol of 60% at currents in excess of 500 mA cm−2. In the modified catalyst, the ratio of ethanol to ethylene is enhanced by a factor of 200 compared to copper catalysts. Analysis by ATR-IR measurements under operating conditions, and by computational simulations, suggests that reduction of CO2 at the copper/gold heterojunction is dominated by generation of the intermediate OCCOH*. The latter is a key contributor in the overall, asymmetrical electrohydrogenation of CO2 giving ethanol rather than ethylen

Hollow Copper Nanocubes Promoting CO₂ Electroreduction to Multicarbon Products

Electrochemical carbon dioxide reduction reaction (CO2RR) to multicarbon (C2+) compounds holds great potential for achieving carbon neutrality and storing intermittent renewable energy. The formation of carbon–carbon (C–C) bonds, affected by the concentration of *CO intermediates on the surface of catalysts, is critical to facilitate the production of C2 species. Here, a novel method to prepare uniform hollow oxide-derived copper crystals is reported, reducing CO2 to C2 products (ethylene and ethanol) with an outstanding Faradaic efficiency of 71.1% in 0.1 M KHCO3. The degree of hollowness shows a positive tendency to C2 selectivity but negative to H2 and C1 selectivity. In situ surface-enhanced infrared absorption spectroscopy indicates that hollow structures enhance localized *CO concentration, boosting C–C coupling for producing C2 products. This provides a feasible strategy to enrich important intermediates to deeper reduction products through catalyst structure engineering