2020 Vol. 5, No. 3

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Editorial
In celebration of the 80th birthday of Professor Wenchuan Wang
Dapeng Cao, Jianzhong Wu, Daojian Cheng
2020, 5(3): 247-248. doi: 10.1016/j.gee.2020.08.003
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Research Highlight
Water-mediated phase-change composite electrolyte
Mingyang Liu, Buxing Han
2020, 5(3): 249-250. doi: 10.1016/j.gee.2020.07.003
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With the world's focus on wearable electronics, the scientific community has anticipated the plasticine-like processability of electrolytes and electrodes. A bioinspired composite of polymer and phase-changing salt with the similar bonding structure to that of natural bones is a suitable electrolyte candidate. Here, Wang et al. reported a water-mediated composite electrolyte by simple thermal mixing of crystallohydrate and polymer. The processable phase-change composites have significantly high mechanical strength and high ionic mobility.
Review article
Thermodynamics at microscales: 3D→2D, 1D and 0D
Kun Dong, Feng Huo, Suojiang Zhang
2020, 5(3): 251-258. doi: 10.1016/j.gee.2020.07.022
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Today, the laws of traditional thermodynamics are facing challenges when science is growing rapidly toward the microscale-world, even quantum hypothesis. In this work, the thermodynamics of nano-confinement and quantum thermodynamics are summarized to illustrate their developments at the microscales.
Research progress in rare earths and their composites based electrode materials for supercapacitors
Subasri Arunachalam, Balakrishnan Kirubasankar, Duo Pan, Hu Liu, Chao Yan, Zhanhu Guo, Subramania Angaiah
2020, 5(3): 259-273. doi: 10.1016/j.gee.2020.07.021
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Supercapacitor is an imminent potential energy storage system, and acts as a booster to the batteries and fuel cells to provide necessary power density. In the last decade, carbon and carbonaceous materials, conducting polymers and transition metal oxide/hydroxide based electrode materials have been made to show a remarkable electrochemical performance. Rare-earth materials have attracted significant research attention as an electrode material for supercapacitor applications based on their physicochemical properties. In this review, rare earth metals, rare earth metal oxides/hydroxides, rare-earth metal chalcogenides, rare-earth metal/carbon composites and rare-earth metal/metal oxide composites based electrode materials are discussed for supercapacitors. We also discuss the energy chemistry of rare-earth metal-based materials. Besides the factors that affect the performance of the electrode materials, their evaluation methods and supercapacitor performances are discussed in details. Finally, the future outlook in rare-earth-based electrode materials is revealed towards its current developments for supercapacitor applications.
Physicochemical properties and structure of fluid at nano-/micro-interface: Progress in simulation and experimental study
Qingwei Gao, Yumeng Zhang, Shuting Xu, Aatto Laaksonen, Yudan Zhu, Xiaoyan Ji, Xiaohua Lu
2020, 5(3): 274-285. doi: 10.1016/j.gee.2020.07.013
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In modern chemical engineering processes, the involvement of solid/fluid interface is the most important component of process intensification techniques, such as confined membrane separation and catalysis. In the review, we summarized the research progress of the latest theoretical and experimental works to elucidate the contribution of interface to the fluid properties and structures at nano- and micro-scale. We mainly focused on water, alcohol aqueous solution, and ionic liquids, because they are classical systems in interfacial science and/or widely involved in the industrialization process. Surface-induced fluids were observed in all reviewed systems and played a critical role in physicochemical properties and structures of outside fluid. It can even be regarded as a new interface, when the adsorption layer has a strong interaction with the solid surface. Finally, we proposed a perspective on scientific challenges in the modern chemical engineering processes and outlined future prospects.
First-principles-aided thermodynamic modeling of transition-metal heterogeneous catalysts: A review
Haoxiang Xu, Daojian Cheng
2020, 5(3): 286-302. doi: 10.1016/j.gee.2020.07.006
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Over the past decade, the first-principles-aided thermodynamic models have become standard theoretical tools in research on structural stability and evolution of transition-metal heterogeneous catalysts under reaction environment. Advances in first-principles-aided thermodynamic models mean it is now possible to enable the operando computational modeling, which provides a deep insight into mechanism behind structural stability and evolution, and paves the way for high-through screening for promising transition-metal heterogeneous catalysts. Here, we briefly review the framework and foundation of first-principles-aided thermodynamic models and highlight its contribution to stability analysis on catalysts and identification of reaction-induced structural evolution of catalyst under reaction environment. The present review is helpful for understanding the ongoing developments of first-principles-aided thermodynamic models, which can be employed to screen high-stability catalysts and predict their structural reconstruction in future rational catalyst design.
Multiscale modeling of electrolytes in porous electrode: From equilibrium structure to non-equilibrium transport
Haolan Tao, Cheng Lian, Honglai Liu
2020, 5(3): 303-321. doi: 10.1016/j.gee.2020.06.020
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Understanding the mechanisms and properties of various transport processes in the electrolyte, porous electrode, and at the interface between electrode and electrolyte plays a crucial role in guiding the improvement of electrolytes, materials and microstructures of electrode. Nanoscale equilibrium properties and nonequilibrium ion transport are substantially different to that in the bulk, which are difficult to observe from experiments directly. In this paper, we introduce equilibrium and no-equilibrium thermodynamics for electrolyte in porous electrodes or electrolyte–electrode interface. The equilibrium properties of electrical double layer (EDL) including the EDL structure and capacitance are discussed. In addition, classical non-equilibrium thermodynamic theory is introduced to help us understand the coupling effect of different transport processes. We also review the recent studies of nonequilibrium ion transport in porous electrode by molecular and continuum methods, among these methods, dynamic density functional theory (DDFT) shows tremendous potential as its high efficiency and high accuracy. Moreover, some opportunities for future development and application of the non-equilibrium thermodynamics in electrochemical system are prospected.
Research paper
A generalized formula for two-dimensional diffusion of CO in graphene nanoslits with different Pt loadings
Chenglong Qiu, Yinbin Wang, Yuejin Li, Xiang Sun, Guilin Zhuang, Zihao Yao, Shengwei Deng, Jianguo Wang
2020, 5(3): 322-332. doi: 10.1016/j.gee.2020.04.012
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Catalytic performance of supported metal catalysts not only depends on the reactivity of metal, but also the adsorption and diffusion properties of gas molecules which are usually affected by many factors, such as temperature, pressure, properties of metal clusters and substrates, etc. To explore the impact of each of these macroscopic factors, we simulated the movement of CO molecules confined in graphene nanoslits with or without supported Pt nanoparticles. The results of molecular dynamics simulations show that the diffusion of gas molecules is accelerated with high temperature, low pressure or low surface-atom number of supported metals. Notably, the supported metal nanoparticles greatly affect the gas diffusion due to the adsorption of gas molecules. Furthermore, to bridge a quantitative relationship between microscopic simulation and macroscopic properties, a generalized formula is derived from the simulation data to calculate the diffusion coefficient. This work helps to advise the diffusion modulation of gas molecules via structural design of catalysts and regulation of reaction conditions.
High-throughput computational screening of Cu-MOFs with open metal sites for efficient C2H2/C2H4 separation
Lei Liu, Lei Wang, Dahuan Liu, Qingyuan Yang, Chongli Zhong
2020, 5(3): 333-340. doi: 10.1016/j.gee.2020.03.002
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Cost effective separation of acetylene (C2H2) and ethylene (C2H4) is of key importance to obtain essential chemical raw materials for polymer industry. Due to the low compression limit of C2H2, there is an urgent demand to develop suitable materials for efficiently separating the two gases under ambient conditions. In this paper, we provided a high-throughput screening strategy to study porous metal-organic frameworks (MOFs) containing open metal sites (OMS) for C2H2/C2H4 separation, followed by a rational design of novel MOFs in-silico. A set of accurate force fields was established from ab initio calculations to describe the critical role of OMS towards guest molecules. From a large-scale computational screening of 916 experimental Cu-paddlewheel-based MOFs, three materials were identified with excellent separation performance. The structure-performance relationships revealed that the optimal materials should have the largest cavity diameter around 5–10 Å and pore volume in-between 0.3-1.0 cm3 g−1. Based on the systematic screening study result, three novel MOFs were further designed with the incorporation of fluorine functional group. The results showed that Cu-OMS and the –F group on the aromatic rings close to Cu sites could generate a synergistic effect on the preferential adsorption of C2H2 over C2H4, leading to a remarkable improvement of C2H2 separation performance of the materials. The findings could provide insight for future experimental design and synthesis of high-performance nanostructured materials for C2H2/C2H4 separation.
Electron paramagnetic resonance studies of the chelate-based ionic liquid in different solvents
Songna Zhang, Xinyu Wang, Jia Yao, Haoran Li
2020, 5(3): 341-346. doi: 10.1016/j.gee.2020.06.018
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The electron paramagnetic resonance spectra of the chelate-based ionic liquid [C10mim][Cu(F6-acac)3] in different solvents have been obtained at 120 K. It was found that the values of the63Cu hyperfine coupling constants (AIL) of [C10mim][Cu(F6-acac)3] in molecular solvents were from 116 to 180 Gauss. Moreover, theAIL values in general ionic liquids are more complicated, and two sets of peaks can often be observed in their electron paramagnetic resonance spectra. Based on the Kamlet–Taft parameters, relative permittivity, the experimental results were discussed in terms of solvation effect and coordination of the solvents.
A continuous and high-efficiency process to separate coal bed methane with porous ZIF-8 slurry: Experimental study and mathematical modelling
Wan Chen, Xiaonan Guo, Enbao Zou, Mengling Luo, Mengzijing Chen, Mingke Yang, Hai Li, Chongzhi Jia, Chun Deng, Changyu Sun, Bei Liu, Lanying Yang, Guangjin Chen
2020, 5(3): 347-363. doi: 10.1016/j.gee.2020.04.015
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Coal bed methane has been considered as an important energy resource. One major difficulty of purifying coal bed methane comes from the similar physical properties of CH4 and N2. The ZIF-8/water-glycol slurry was used as a medium to separate coal bed methane by fluidifying the solid adsorbent material. The sorption equilibrium experiment of binary mixture (CH4/N2) and slurry was conducted. The selectivity of CH4 to N2 is within the range of 2–6, which proved the feasibility of the slurry separation method. The modified Langmuir equation was used to describe the gas-slurry phase equilibrium behavior, and the calculated results were in good agreement with the experimental data. A continuous absorption–adsorption and desorption process on the separation of CH4/N2 in slurry is proposed and its mathematical model is also developed. Sensitivity analysis is conducted to determine the operation conditions and the energy performance of the proposed process was also evaluated. Feed gas contains 30 mol% of methane and the methane concentration in product gas is 95.46 mol% with the methane recovery ratio of 90.74%. The total energy consumption for per unit volume of product gas is determined as 1.846 kWh Nm−3. Experimental results and process simulation provide basic data for the design and operation of pilot and industrial plant.
Role of substrate softness in stabilizing surface nanobubbles
Changsheng Chen, Xianren Zhang, Dapeng Cao
2020, 5(3): 374-380. doi: 10.1016/j.gee.2020.07.008
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The contact line pinning and supersaturation theory for the nanobubble stability has attracted extensive concerns from experimental investigators, and some experimenters argue that the contact line pinning is unnecessary. To interpret the experimental observations, we have proposed previously through molecular dynamics simulations that the deformation of soft substrates caused by surface nanobubbles may play an important role in stabilizing surface nanobubbles, while yet no quantitative theory is available for explanation of this mechanism. Here, the detailed mechanism of self-pinning-induced stability of surface nanobubbles is investigated through theoretical analysis. By manipulating substrate softness, we find that the formation of surface nanobubbles may create a deformation ridge nearby their contact lines which leads to the self-pinning effect. Theoretical analysis shows that the formation of nanobubbles on sufficiently rigid substrates or on liquid–liquid interfaces corresponds to a local free energy maximum, while that on the substrates with intermediate softness corresponds to a local minimum. Thus, the substrate softness could regulate the surface nanobubble stability. The critical condition for the self-pinning effect is determined based on contact line depinning, and the effect of gas supersaturation is explored. Finally, the approximate stability range for the surface nanobubbles is also predicted.
Research article
Computational screening and design of nanoporous membranes for efficient carbon isotope separation
Jingqi Wang, Musen Zhou, Diannan Lu, Weiyang Fei, Jianzhong Wu
2020, 5(3): 364-373. doi: 10.1016/j.gee.2020.07.025
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Stable isotopes have been routinely used in chemical sciences, medical treatment and agricultural research. Conventional technologies to produce high-purity isotopes entail lengthy separation processes that often suffer from low selectivity and poor energy efficiency. Recent advances in nanoporous materials open up new opportunities for more efficient isotope enrichment and separation as the pore size and local chemical environment of such materials can be engineered with atomic precision. In this work, we demonstrate the unique capability of nanoporous membranes for the separation of stable carbon isotopes by computational screening a materials database consisting of 12,478 computation-ready, experimental metal-organic frameworks (MOFs). Nanoporous materials with the highest selectivity and membrane performance scores have been identified for separation of12CH4/13CH4 at the ambient condition (300 K). Analyzing the structural features and metal sites of the promising MOF candidates offers useful insights into membrane design to further improve the performance. An upper limit of the efficiency has been identified for the separation of 12CH4/13CH4 with the existing MOFs and those variations by replacement of the metal sites.

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