Fe based MOF encapsulating triethylenediamine cobalt complex to prepare a FeN3-CoN3 dual-atom catalyst for efficient ORR in Zn-air batteries.

Single-atom catalysts show good oxygen reduction reaction (ORR) performance in metal-air battery. However, the symmetric electron distribution results in discontented adsorption energy of ORR intermediates and a lower ORR activity. Herein, Fe-Co dual-atom catalyst with FeN3-CoN3 configuration was prepared by encapsulating nitrogen-rich ion (triethylenediamine cobalt complex, [Co(en)3]3+) in Fe based MOF cage to greatly enhance ORR performance. Due to the confinement effect of the MOF cage, the encapsulated [Co(en)3]3+ is closer to Fe of MOF, thus easily generating FeN3-CoN3 sites. The FeN3-CoN3 sites can break the symmetric electron distribution of single-atom sites, optimizing adsorption energy of oxygen intermediate. Thus, FeCo-NC exhibits extraordinary ORR activity with a high half-wave potential of 0.915 V and 0.789 V in alkaline and acidic electrolyte, respectively, while it was 0.874 V and 0.79 V for Pt/C. The liquid and solid Zn-air batteries with FeCo-NC as cathode show higher peak power density and specific capacity. DFT results indicate that FeN3-CoN3 site can reduce the reaction energy barrier of the rate-determining step resulting in an excellent ORR performance.

Synchronous Design of Membrane Material and Process for Pre-Combustion CO2 Capture: A Superstructure Method Integrating Membrane Type Selection.

Membrane separation technology for CO2 capture in pre-combustion has the advantages of easy operation, minimal land use and no pollution and is considered a reliable alternative to traditional technology. However, previous studies only focused on the H2-selective membrane (HM) or CO2-selective membrane (CM), paying little attention to the combination of different membranes. Therefore, it is hopeful to find the optimal process by considering the potential combination of H2-selective and CO2-selective membranes. For the CO2 capture process in pre-combustion, this paper presents an optimization model based on the superstructure method to determine the best membrane process. In the superstructure model, both CO2-selective and H2-selective commercial membranes are considered. In addition, the changes in optimal membrane performance and capture cost are studied when the selectivity and permeability of membrane change synchronously based on the Robeson upper bound. The results show that when the CO2 purity is 96% and the CO2 recovery rate is 90%, the combination of different membrane types achieves better results. The optimal process is the two-stage membrane process with recycling, using the combination of CM and HM in all situations, which has obvious economic advantages compared with the Selexol process. Under the condition of 96% CO2 purity and 90% CO2 recovery, the CO2 capture cost can be reduced to 11.75$/t CO2 by optimizing the process structure, operating parameters, and performance of membranes.

An Energy-Economic-Environment Tri-Objective Evaluation Method for Gas Membrane Separation Processes of H2/CO2.

For pre-combustion carbon capture, the high syngas pressure provides a sufficient mass transfer driving force to make the gas membrane separation process an attractive option. Comparisons of combined different membrane materials (H2-selective and CO2-selective membranes) and membrane process layouts are very limited. Especially, the multi-objective optimization of such processes requires further investigation. Therefore, this paper proposes 16 two-stage combined membranes system for pre-combustion CO2 capture, including 4 two-stage H2-selective membrane systems, 4 two-stage CO2-selective membrane systems, and 8 two-stage hybrid membrane systems. A tri-objective optimization method of energy, economy, and environment is proposed for comprehensive evaluation of the proposed systems. Results show that with the targets of 90% CO2 purity and recovery, six gas membrane separation systems could be satisfied. After further multi-objective optimization and comparison, the C1H2-4 system (the hybrid system with H2-selective membranes and CO2-selective membranes) has the best performance. Feed composition and separation requirements also have an important influence on the multi-objective optimization results. The effects of selectivity and permeance of H2-selective and CO2-selective membranes on the performance of the C1H2-4 system are also significant.

Co3O4 Nanosheets Preferentially Growing (220) Facet with a Large Amount of Surface Chemisorbed Oxygen for Efficient Oxidation of Elemental Mercury from Flue Gas.

Oxygen vacancies can capture and activate gaseous oxygen, forming surface chemisorbed oxygen, which plays an important role in the Hg0 oxidation process. Fine control of oxygen vacancies is necessary and a major challenge in this field. A novel method for facet control combined with morphology control was used to synthesize Co3O4 nanosheets preferentially growing (220) facet to give more oxygen vacancies. X-ray photoelectron spectroscopy (XPS) results show that the (220) facet has a higher Co3+/Co2+ ratio, leading to more oxygen vacancies via the Co3+ reduction process. Density functional theory (DFT) calculations confirm that the (220) facet has a lower oxygen vacancy formation energy. Furthermore, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results suggest that Co3O4 nanosheets yield more defects during the synthesis process. These results are the reasons for the greater number of oxygen vacancies in Co3O4 nanosheets, which is confirmed by electron energy loss spectroscopy (EELS), Raman spectroscopy, and photoluminescence (PL) spectroscopy. Therefore, Co3O4 nanosheets show excellent Hg0 removal efficiency over a wide temperature range of 100-350 °C at a high gas hourly space velocity (GHSV) of 180 000 h-1. Additionally, the catalytic efficiency of Co3O4 nanosheets is still greater than 83%, even after 80 h of testing, and it recovers to its original level after 2 h of in situ thermal treatment at 500 °C.

Effect of Hydrogen-Bonding Interaction on the Arrangement and Dynamics of Water Confined in a Polyamide Membrane: A Molecular Dynamics Simulation.

An increasing demand for freshwater inspires further understanding of the mechanism of water diffusion in reverse-osmosis membranes for the development of high-performance membranes for desalination. Water diffusion has a close relationship with the structural and dynamical characteristics of hydrogen bonds, which is not well-understood for the confining environment inside the polyamide membrane at the molecular level. In this work, an atomistic model of a highly cross-linked polyamide membrane was built with an equilibrated mixture of m-phenylenediamine and trimesoyl chloride monomers. The structure and dynamics of water in the regions from the bulk phase to the membrane interior were investigated by molecular dynamics simulations. Explicit hydrogen bond criteria were determined for hydrogen-bonding analysis. The local distribution and orientation of water reveal that the hydrogen-bonding affinity of the hydrophilic functional groups of polymers inhibits water diffusion inside the membrane. The affinity helps to produce percolated water channels across the membrane. The hydrogen-bonding structures of water in different regions indicate dehydration is required for the entry of water into the polyamide membrane, which dominates water flux across the membrane. This paper not only deepens the understanding of the structure and dynamics of water confined in the polyamide membrane but also stimulates the future work on high-performance reverse-osmosis membranes.

[Cleistogenes squarrosa population at different restorative succession stages in Inner Mongolia of China: a point pattern analysis].

In this paper, the spatial pattern of Cleistogenes squarrosa population in different restorative succession communities of the typical steppe dominated by Stipa grandis and Leymus chinensis in Inner Mongolia was measured by photography orientation, and analyzed by complete spatial randomness model, Poisson cluster process, and nested double-cluster process. In severely degraded community, C. squarrosa population fitted well nested double-cluster process for all scales, i. e., high density small clusters existed at the centers of large clusters; whereas in 5-, 8-, and 21-year-old restored communities, C. squarrosa population fitted well Poisson cluster process for all scales, i. e. , high density small clusters did not exist at the centers of the clusters. It was suggested that facilitation was the dominant interaction in severely degraded community, while competition dominated in restored communities. The differences in the spatial pattern of C. squarrosa population during the restorative succession could be induced by the shift from facilitation to competition along the gradient of grazing stress.