Feb 2021, Volume 15 Issue 1

Cover illustration

  • (Faraz Montazersadgh, Hao Zhang, Anas Alkayal, Benjamin Buckley, Ben W. Kolosz, Bing Xu, Jin Xuan, pp. 937‒947)
    The cover image shows the vision of our e-bio-fuel project, joint funded by the UK’s Department of Transport and SuperGen Bioenergy Hub in 2019. It aims to develop a new electrochemical platform to produce low-carbon fuels through integrated co-valorisation of [Detail] ...

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    Weiping Wu, Xiaolei Fan, Yongliang Li, Ruijiao Dong
    Sainab Omar, Yang Yang, Jiawei Wang

    This review article summarizes the key published research on the topic of bio-oil upgrading using catalytic and non-catalytic supercritical fluid (SCF) conditions. The precious metal catalysts Pd, Ru and Pt on various supports are frequently chosen for catalytic bio-oil upgrading in SCFs. This is reportedly due to their favourable catalytic activity during the process including hydrotreating, hydrocracking, and esterification, which leads to improvements in liquid yield, heating value, and pH of the upgraded bio-oil. Due to the costs associated with precious metal catalysts, some researchers have opted for non-precious metal catalysts such as acidic HZSM-5 which can promote esterification in supercritical ethanol. On the other hand, SCFs have been effectively used to upgrade crude bio-oil without a catalyst. Supercritical methanol, ethanol, and water are most commonly used and demonstrate catalyst like activities such as facilitating esterification reactions and reducing solid yield by alcoholysis and hydrolysis, respectively.

    Wenjie Sun, Jiale Mao, Shuang Wang, Lei Zhang, Yonghong Cheng

    Polymer-based dielectric capacitors are widely-used energy storage devices. However, although the functions of dielectrics in applications like high-voltage direct current transmission projects, distributed energy systems, high-power pulse systems and new energy electric vehicles are similar, their requirements can be quite different. Low electric loss is a critical prerequisite for capacitors for electric grids, while high-temperature stability is an essential pre-requirement for those in electric vehicles. This paper reviews recent advances in this area, and categorizes dielectrics in terms of their foremost properties related to their target applications. Requirements for polymer-based dielectrics in various power electronic equipment are emphasized, including high energy storage density, low dissipation, high working temperature and fast-response time. This paper considers innovations including chemical structure modification, composite fabrication and structure re-design, and the enhancements to material performances achieved. The advantages and limitations of these methods are also discussed.

    Tong Zhang, Shan-Jiang Wang, Xiao-Yang Zhang, Ming Fu, Yi Yang, Wen Chen, Dan Su

    Nanostructure-based broadband absorbers are prominently attractive in various research fields such as nanomaterials, nanofabrication, nanophotonics and energy utilization. A highly efficient light absorption in wider wavelength ranges makes such absorbers useful in many solar energy harvesting applications. In this review, we present recent advances of broadband absorbers which absorb light by nanostructures. We start from the mechanism and design strategies of broadband absorbers based on different materials such as carbon-based, plasmonic or dielectric materials and then reviewed recent progress of solar energy thermal utilization dependent on the superior photo-heat conversion capacity of broadband absorbers which may significantly influence the future development of solar energy utilization, seawater purification and photoelectronic device design.

    Huaiwei Shi, Teng Zhou

    Functional materials are widely used in chemical industry in order to reduce the process cost while simultaneously increase the product quality. Considering their significant effects, systematic methods for the optimal selection and design of materials are essential. The conventional synthesis-and-test method for materials development is inefficient and costly. Additionally, the performance of the resulting materials is usually limited by the designer’s expertise. During the past few decades, computational methods have been significantly developed and they now become a very important tool for the optimal design of functional materials for various chemical processes. This article selectively focuses on two important process functional materials, namely heterogeneous catalyst and gas separation agent. Theoretical methods and representative works for computational screening and design of these materials are reviewed.

    Ammaru Ismaila, Xueli Chen, Xin Gao, Xiaolei Fan

    Thermodynamic chemical equilibrium analysis of steam reforming of glycerol (SRG) for selective hydrogen production was performed based on the Gibbs free energy minimisation method. The ideal SRG reaction (C3H8O3+3H2O→3CO2+7H2) and a comprehensive set of side reactions during SRG are considered for the formation of a wide range of products. Specifically, this work focused on the analysis of formation of H2, CO2, CO and CH4 in the gas phase and determination of the carbon free region in SRG under the conditions at atmospheric pressure, 600 K–1100 K and 1.013 × 105–1.013 × 106 Pa with the steam-to-glycerol feed ratios (SGFR) of 1:5–10. The reaction conditions which favoured SRG for H2 production with minimum coke formation were identifies as: atmospheric pressure, temperatures of 900 K–1050 K and SGFR of 10:1. The influence of using the inert carrier gas (i.e., N2) in SRG was studied as well at atmospheric pressure. Although the presence of N2 in the stream decreased the partial pressure of reactants, it was beneficial to improve the equilibrium yield of H2. Under both conditions of SRG (with/without inert gas), the CH4 production is minimised, and carbon formation was thermodynamically unfavoured at steam rich conditions of SGFR>5:1.

    Yingjie Ma, Nan Zhang, Jie Li, Cuiwen Cao

    The extractive dividing-wall column (EDWC) is one of the most efficient technologies for separation of azeotropic or close boiling-point mixtures, but its design is fairly challenging. In this paper we extend the hybrid feasible path optimisation algorithm (Ma Y, McLaughlan M, Zhang N, Li J. Computers & Chemical Engineering, 2020, 143: 107058) for such optimal design. The tolerances-relaxation integration method is refined to allow for long enough integration time that can ensure the solution of the pseudo-transient continuation simulation close to the steady state before the required tolerance is used. To ensure the gradient and Jacobian information available for optimisation, we allow a relaxed tolerance for the simulation in the sensitivity analysis mode when the simulation diverges under small tolerance. In addition, valid lower bounds on purity of the recycled entrainer and the vapour flow rate in column sections are imposed to improve computational efficiency. The computational results demonstrate that the extended hybrid algorithm can achieve better design of the EDWC compared to those in literature. The energy consumption can be reduced by more than 20% compared with existing literature report. In addition, the optimal design of the heat pump assisted EDWC is achieved using the improved hybrid algorithm for the first time.

    Wenqian Chen, Vikram Karde, Thomas N. H. Cheng, Siti S. Ramli, Jerry Y. Y. Heng

    Understanding the nature of hydrophobicity has fundamental importance in environmental applications. Using spherical silica nanoparticles (diameter= 369 ± 7 nm) as the model material, the current study investigates the relationship between the alkyl chain network and hydrophobicity. Two alkyl silanes with different chain length (triethoxymethylsilane (C1) vs. trimethoxy(octyl)silane (C8)) were utilised separately for the functionalisation of the nanoparticles. Water contact angle and inverse gas chromatography results show that the alkyl chain length is essential for controlling hydrophobicity, as the octyl-functionalised nanoparticles were highly hydrophobic (water contact angle= 150.6° ± 6.6°), whereas the methyl-functionalised nanoparticles were hydrophilic (i.e., water contact angle= 0°, similar to the pristine nanoparticles). The homogeneity of the octyl-chain network also has a significant effect on hydrophobicity, as the water contact angle was reduced significantly from 148.4° ± 3.5° to 30.5° ± 1.0° with a methyl-/octyl-silane mixture (ratio= 160:40 µL·g–1 nanoparticles).

    Ling Tan, Kipkorir Peter, Jing Ren, Baoyang Du, Xiaojie Hao, Yufei Zhao, Yu-Fei Song

    The rational design of photocatalyst that can effectively reduce CO2 under visible light (l>400 nm), and simultaneously precise control of the products syngas (CO/H2) ratio is highly desirable for the Fischer-Tropsch reaction. In this work, we synthesized a series of CeO2-decorated layered double hydroxides (LDHs, Ce-x) samples for photocatalytic CO2 reduction. It was found that the selectivity and productivity of CO and H2 from photoreduction of CO2 in conjunction with Ru-complex as photosensitizer performed an obvious “volcano-like” trend, with the highest point at Ce-0.15 and the CO/H2 ratio can be widely tunable from 1/7.7 to 1/1.3. Furthermore, compared with LDH, Ce-0.15 also drove photocatalytic CO2 to syngas under 600 nm irradiation. It implied that an optimum amount of CeO2 modifying LDH promoted the photoreduction of CO2 to syngas. This report gives the way to fully utilize the rare earth elements and provides a promising route to enhance the photo-response ability and charge injection efficiency of LDH-based photocatalysts in the synthesis of syngas with a tunable ratio under visible light irradiation.

    Feng Sun, Jinren Lu, Yuhong Wang, Jie Xiong, Congjie Gao, Jia Xu

    Surface engineering with polydopamine coatings has been considered a promising surface functionalisation tool. However, it is difficult to control the self-polymerisation for polydopamine formation, which usually causes severe interparticle aggregation. In this study, polydopamine self-polymerisation was controlled by adjusting its reducing environment using a reductant (NaBH4) to fabricate mixed cellulose ester (MCE)/polydopamine membranes. An oxidising environment using NaIO4 was additionally tested as the control. The results showed that a thin polydopamine coating with small polydopamine particles was formed on the skeleton frameworks of the MCE membrane with NaBH4, and the self-polymerisation rate was suppressed. The polydopamine coating formed in the reducing environment facilitated excellent water transport performance with a water permeance of approximately 400 L·m−2·h−1·bar−1 as well as efficient organic foulant removal with a bovine serum albumin rejection of approximately 90%. In addition, the polydopamine coating with NaBH4 exhibited both excellent chemical stability and anti-microbial activity, demonstrating the contribution of the reducing environment to the performance of the MCE/polydopamine membranes. It shows significant potential for use in water purification.

    Jie Liu, Jiahao Shen, Jingjing Wang, Yuan Liang, Routeng Wu, Wenwen Zhang, Delin Shi, Saixiang Shi, Yanping Wang, Yimin Wang, Yumin Xia

    To enhance the solubility of polyanilines (PANI), polymeric ionic liquid (PIL) was introduced into the polymerization synthesis of PANI with various proportions. The structure and properties of the modified PANIs were characterized by 1H NMR, Fourier transform infrared spectroscopy, thermogravimetric analysis, ultraviolet-visible spectrum, etc. It was found that the obtained PANIs doped with PILs were soluble in various organic solvents such as N,N-dimethyl formamide and acetonitrile. Compared with the pure PANI, the PANIs doped by PILs showed remarkable solubility and their chemical structure and conductivity kept integrated.

    Leijing Liu, Hao Zhang, Bo Xiao, Yang Liu, Bin Xu, Chen Wang, Shanpeng Wen, Erjun Zhou, Gang Chen, Chan Im, Wenjing Tian

    Effects of a benzotriazole (BTA)-based small molecule, BTA2, as the third component on the charge carrier generation and recombination behavior of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) organic solar cells (OSCs) were investigated by optical simulation of a transfer matrix model (TMM), photo-induced charge extraction by linearly increasing voltage (photo-CELIV) technique, atomic force microscope (AFM), and the Onsager–Braun model analysis. BTA2 is an A2-A1-D-A1-A2-type non-fullerene small molecule with thiazolidine-2,4-dione, BTA, and indacenodithiophene as the terminal acceptor (A2), bridge acceptor (A1), and central donor (D), respectively. The short-circuit current density of the OSCs with BTA2 can be enhanced significantly owing to a complementary absorption spectrum. The optical simulation of TMM shows that the ternary OSCs exhibit higher internal absorption than the traditional binary OSCs without BTA2, resulting in more photogenerated excitons in the ternary OSCs. The photo-CELIV investigation indicates that the ternary OSCs suffer higher charge trap-limited bimolecular recombination than the binary OSCs. AFM images show that BTA2 aggravates the phase separation between the donor and the acceptor, which is disadvantageous to charge carrier transport. The Onsager-Braun model analysis confirms that despite the charge collection efficiency of the ternary OSCs being lower than that of the binary OSCs, the optimized photon absorption and exciton generation processes of the ternary OSCs achieve an increase in photogenerated current and thus improve power conversion efficiency.

    Tianyu Yao, Haiyan Yang, Kui Wang, Haiyan Jiang, Xiao-Bo Chen, Hezhou Liu, Qudong Wang, Wenjiang Ding

    Effects of NaI as an additive on electrodeposition of Al coatings in AlCl3-NaCl-KCl (80-10-10 wt-%) molten salts electrolyte at 150 °C were investigated by means of cyclic voltammetry, chronopotentiometry, scanning electron microscopy and X-ray diffraction (XRD). Results reveal that addition of NaI in the electrolyte intensifies cathodic polarization, inhibits growth of Al deposits and increases number density of charged particles. The electrodeposition of Al coatings in the AlCl3-NaCl-KCl molten salts electrolyte proceeds via three-dimensional instantaneous nucleation which however exhibits irrelevance with NaI. Galvanostatic deposition results indicate that NaI could facilitate the formation of uniform Al deposits. A compact coating consisting of Al deposits with an average particle size of 3 μm was obtained at a current density of 50 mA∙cm−2 in AlCl3-NaCl-KCl molten salts electrolyte with 10 wt-% NaI. XRD analysis confirmed that NaI could contribute to the formation of Al coating with a preferred crystallographic orientation along (220) plane.

    Shilei Ding, Zelong Jiang, Jing Gu, Hongliang Zhang, Jiajia Cai, Dongdong Wang

    In this paper, two carbon-coated lithium titanate (LTO-C1 and LTO-C2) composites were synthesized using the ball-milling-assisted calcination method with different carbon precursor addition processes. The physical and electrochemical properties of the as-synthesized negative electrode materials were characterized to investigate the effects of two carbon-coated LTO synthesis processes on the electrochemical performance of LTO. The results show that the LTO-C2 synthesized by using Li2CO3 and TiO2 as the raw materials and sucrose as the carbon source in a one-pot method has less polarization during lithium insertion and extraction, minimal charge transfer impedance value and the best electrochemical performance among all samples. At the current density of 300 mA·h·g–1, the LTO-C2 composite delivers a charge capacity of 126.9 mA·h·g–1, and the reversible capacity after 300 cycles exceeds 121.3 mA·h·g–1 in the voltage range of 1.0–3.0 V. Furthermore, the electrochemical impedance spectra show that LTO-C2 has higher electronic conductivity and lithium diffusion coefficient, which indicates the advantages in electrode kinetics over LTO and LTO-C1. The results clarify the best electrochemical properties of the carbon-coated LTO-C2 composite prepared by the one-pot method.

    Lifeng Zhang, Yifei Song, Weiping Wu, Robert Bradley, Yue Hu, Yi Liu, Shouwu Guo

    Unique self-assembled iron(II) molybdenum(IV) oxide (Fe2Mo3O8) mesoporous hollow spheres have been facilely constructed via the bubble-template-assisted hydrothermal synthesis method combined with simple calcination. The compact assembly of small nanoparticles on the surface of the hollow spheres not only provides more active sites for the Fe2Mo3O8, but also benefits the stability of the hollow structure, and thus improved the lithium storage properties of Fe2Mo3O8. The Fe2Mo3O8 mesoporous hollow spheres exhibit high initial discharge and charge capacities of 1189 and 997 mA∙h∙g1 respectively, as well as good long-term cycling stability (866 mA∙h∙g1 over 70 cycles) when used as a lithium-ion battery anode. This feasible material synthesis strategy will inspire the variation of structural design in other ternary metal molybdates.

    Boa Jin, Hyunmin Park, Yang Liu, Leijing Liu, Jongdeok An, Wenjing Tian, Chan Im

    To understand the complex behaviors of photogenerated charge carriers within polymer-based bulk-heterojunction-type solar cells, the charge-carrier photogeneration and extraction dynamics are simultaneously estimated using a transient photocurrent technique under various external-bias voltages, and a wide range of excitation intensities are analyzed. For this purpose, conventional devices with 80 nm thick active layers consisting of a blend of representative P3HT and PTB7 electron-donating polymers and proper electron-accepting fullerene derivatives were used. After the correction for the saturation behavior at a high excitation-intensity range nearby the regime of the space charge-limited current, the incident-photon-density-dependent maximum photocurrent densities at the initial peaks are discussed as the proportional measures of the charge-carrier-photogeneration facility. By comparing the total number of the extracted charge carriers to the total number of the incident photons and the number of the initially photogenerated charge carriers, the external quantum efficiencies as well as the extraction quantum efficiencies of the charge-carrier collection during a laser-pulse-induced transient photocurrent process were obtained. Subsequently, the charge-carrier concentration-dependent mobility values were obtained, and they are discussed in consideration of the additional influences of the charge-carrier losses from the device during the charge-carrier extraction that also affects the photocurrent-trace shape.

    Yaqin Wang, Lin Yang, Chunxiang Dall’Agnese, Gang Chen, Ai-Jun Li, Xiao-Feng Wang

    SnO2 has been proven to be an effective electron transport layer (ETL) material for perovskite solar cells (PSCs) owing to its excellent electrical and optical properties. Here, we introduce a viable spray coating method for the preparation of SnO2 films. Then, we employ a SnO2 film prepared using the spray coating method as an ETL for PSCs. The PSC based on the spray-coated SnO2 ETL achieves a power conversion efficiency of 17.78%, which is comparable to that of PSCs based on conventional spin-coated SnO2 films. The large-area SnO2 films prepared by spray coating exhibit good repeatability for device performance. This study shows that SnO2 films prepared by spray coating can be applied as ETLs for stable and high-efficiency PSCs. Because the proposed method involves low material consumption, it enables the low-cost and large-scale production of PSCs.

    Yonghyun Kim, Huiwen Liu, Yi Liu, Boa Jin, Hao Zhang, Wenjing Tian, Chan Im

    Cesium lead halide perovskite (CsPbX3, X= Cl, Br, I) quantum dots (QDs) and their partly Mn2+-substituted QDs (CsPb1–xMnxX3) attract considerable attention owing to their unique photoluminescence (PL) efficiencies. The two types of QDs, having different PL decay dynamics, needed to be further investigated in a form of aggregates to understand their solid-state-induced exciton dynamics in conjunction with their behaviors upon degradation to achieve practical applications of those promising QDs. However, thus far, these QDs have not been sufficiently investigated to obtain deep insights related to the long-term stability of their PL properties as aggregated solid-states. Therefore, in this study, we comparatively examined CsPbX3- and CsPb1–xMnxX3-type QDs stocked for>50 d under dark ambient conditions by using excitation wavelength-dependent PL quantum yield and time-resolved PL spectroscopy. These investigations were performed with powder samples in addition to solutions to determine the influence of the inter-QD interaction of the aged QD aggregates on their radiative decays. It turns out that the Mn2+-substituted QDs exhibited long-lasting PL quantum efficiencies, while the unsubstituted CsPbX3-type QDs exhibited a drastic reduction of their PL efficiencies. And the obtained PL traces were clearly sensitive to the sample status. This is discussed with the possible interaction depending on the size and distance of the QD aggregates.

    Lisa Xu, Kaifei Chen, George Q. Chen, Sandra E. Kentish, Gang (Kevin) Li

    The demand for lithium has been steadily growing in recent years due to the boom of electric cars. High purity lithium is commonly used in the manufacture of battery grade lithium electrolyte. Sulfate residuals originating from acid leaching of lithium ores must be limited to below 20 mg·L1 during refining. There are methods to remove sulfate such as membrane processing and chemical precipitation using barium salts. However, membrane separation is unable to achieve the required purity while chemical precipitation often causes secondary contamination with barium and requires extra filtration processes that lead to increased processing costs. In this study, we developed a polymeric matrix entrapped with barium ions as a novel adsorbent to selectively adsorb sulfate in aqueous solutions. The adsorbent was prepared by dropwise injection method where alginate droplets were crosslinked with barium to form hydrogel microcapsules. In a typical scenario, the microcapsules had a diameter of 3 mm and contained 5 wt-% alginate. The microcapsules could successfully reduce sulfate concentration in a solution from 100 to 16 mg·L1, exceeding the removal target. However, the microcapsules were mechanically unstable in the presence of an excess amount of sulfate. Hence, calcium ions were added as a secondary crosslinking agent to improve the integrity of the microcapsules. The two-step Ca/Ba@alginate microcapsules showed an exceptional adsorption performance, reducing the sulfate concentration to as low as 0.02 mg·L1. Since the sulfate selective microcapsules can be easily removed from the aqueous system and do not result in secondary barium contamination, these Ca/Ba@alginate adsorbents will find applications in ultra-refining of lithium in industry.

    Faraz Montazersadgh, Hao Zhang, Anas Alkayal, Benjamin Buckley, Ben W. Kolosz, Bing Xu, Jin Xuan

    Utilizing CO2 in an electro-chemical process and synthesizing value-added chemicals are amongst the few viable and scalable pathways in carbon capture and utilization technologies. CO2 electro-reduction is also counted as one of the main options entailing less fossil fuel consumption and as a future electrical energy storage strategy. The current study aims at developing a new electrochemical platform to produce low-carbon e-biofuel through multifunctional electrosynthesis and integrated co-valorisation of biomass feedstocks with captured CO2. In this approach, CO2 is reduced at the cathode to produce drop-in fuels (e.g., methanol) while value-added chemicals (e.g., selective oxidation of alcohols, aldehydes, carboxylic acids and amines/amides) are produced at the anode. In this work, a numerical model of a continuous-flow design considering various anodic and cathodic reactions was built to determine the most techno-economically feasible configurations from the aspects of energy efficiency, environment impact and economical values. The reactor design was then optimized via parametric analysis.

    Xinghong Duo, Lingchuang Bai, Jun Wang, Jintang Guo, Xiangkui Ren, Shihai Xia, Wencheng Zhang, Abraham Domb, Yakai Feng