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2018, Vol. 27, No. 4　Online: 2018-07-15


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Flexible perovskite solar cells: green, roll-to-roll fabrication

This review presents recent developments in the continuous roll-to-roll printing of perovskite solar cells. As the power conversion efficiency of the perovskite solar cells has been skyrocketed to as high as over 23%, it may become a disruptive technology in the photovoltaics. It reviews commercially available flexible substrates, perovskite solar cells and fabrication processes. In particular, it provides a perspective on low cost solution printing for large-scale high throughput production with a focus on green processing.

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Preface

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A new, sustainable process for synthesis of ethylene glycol Jinlong Gong 2018, 27(4): 949-950.  DOI: 10.1016/j.jechem.2018.04.005 摘要 ( 1356 )

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High performance perovskite solar cells using TiO2 nanospindles as ultrathin mesoporous layer Yinhua Lv, Bing Cai, Yihui Wu, Shubo Wang, Qike Jiang, Qingshan Ma, Jingyue(Jimmy) Liu, Wen-Hua Zhang 2018, 27(4): 951-956.  DOI: 10.1016/j.jechem.2018.01.020 摘要 ( 1454 )   Single crystal anatase TiO2 nanospindles (NSs) with highly exposed {101} facets were synthesized and employed as electron transport materials (ETMs) in perovskite solar cells (PSCs). Time-resolved photoluminescence (TRPL) spectra revealed that the TiO2 NSs are more effective than TiO2 nanoparticles in accepting electrons from perovskite. Moreover, the TiO2 nanospindles further endowed the PSCs with good reproducibility and suppressed hysteresis. The best device with TiO2 NSs as ETMs yielded power conversion efficiency (PCE) of 19.6%, demonstrating that the home-made TiO2 NSs is a good ETM for PSCs.

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All carbon non-covalent exohedral hybrids: C60 aggregates on nanotube networks Evgenee Yekymov, Céline Bounioux, Racheli Itzhak-Cohen, Leila Zeiri, Emil Shahnazaryan, Eugene A. Katz, Rachel Yerushalmi-Rozen 2018, 27(4): 957-961.  DOI: 10.1016/j.jechem.2017.10.035 摘要 ( 1594 )   Exohedral van der Waals (vdW) hybrids comprising pristine carbon nanotubes (CNTs) and C60 fullerenes are expected to enable the engineering of carbonaceous materials with tunable physical and chemical properties due to the unperturbed sp2 hybridization of the comprising allotropes. In spite of theoretical predictions, experimental realization of exohedral non-covalent hybridization of unmodified C60 fullerenes and CNTs was not reported before, probably due to the relatively strong inter-fullerene and inter-tube interactions that drive the system toward phase separation and the formation of fullerene crystals and CNTs bundles. Here we describe a two-step process for preparation of C60-CNTs hybrids. The first step is based on solution-assembly of random, 3D-networks of individual, pristine CNTs followed by fast solvent-quenching. In the second step sublimated fullerenes are deposited onto the pre-assembled networks where structural defects serve as nucleation points for fullerite nanocrystals. Annealing at low temperature (80℃) results in re-organization of the C60 nanocrystals into nanometric layers, forming a CNT-C60 core-shell like cylindrical hybrids. Raman characterization and the observed high mobility of the fullerenes at the CNT surface support the assumption that the exohedral hybrids are of vdW type. The approach presented here offers a pathway for preparation of exohedral hybrids with controlled nanomorphology:CNTs-networks decorated by nanometric C60 crystals and CNTs-3D-networks coated by a shell of non-covalently bonded mono-or multi-layers of C60 molecules that may serve to shape the nanomorphology of the active layer in polymer-fullerene bulk-heterojunction solar cells.

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Tin oxide (SnO2) as effective electron selective layer material in hybrid organic-inorganic metal halide perovskite solar cells Guang Yang, Pingli Qin, Guojia Fang, Gang Li 2018, 27(4): 962-970.  DOI: 10.1016/j.jechem.2018.03.018 摘要 ( 1470 )   The emergence of hybrid organic-inorganic metal halide perovskite solar cells (PSCs) causes a breakthrough in the solar technology recently due to its superior optoelectronic properties and the low-cost fabrication processes. The dramatic enhancement in power conversion efficiency (PCE) of PSCs from 3.8% in 2009 to the recent certified record PCE of 22.7% indicates huge potential of PSCs for future high efficiency and large scale photovoltaic manufacturing. The electron selective layer (ESL) plays an important role in electron extraction and hole blocking function in PSCs, and there have been great interest in developing efficient ESL materials. Recently, tin oxide (SnO2) as an ESL has attracted significant research attentions owing to its low temperature preparation processes as well as yielding high PCE and good stability of PSCs. In this perspective article, we focus on the development progress of SnO2 as an ESL in PSCs, and discuss the strategies for preparing SnO2 to achieve PSCs with high efficiency, less hysteresis and good device stability

Review

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Flexible perovskite solar cells based on green, continuous roll-to-roll printing technology Wei Zi, Zhiwen Jin, Shengzhong Liu, Baomin Xu 2018, 27(4): 971-989.  DOI: 10.1016/j.jechem.2018.01.027 摘要 ( 1529 )   By designing and fabricating thin film electronic devices on a flexible substrate instead of more commonly used rigid substrate, flexible electronics produced has opened a field of special applications. In this article, we first reviewed available products that may be used as flexible substrates, their characteristics and unique advantages as supporting material for flexible electronic devices. Secondly, flexible perovskite solar cell is examined in detail, with special focus on its potential large-scale fabrication processes. In particular, a comprehensive review is provided on low cost solution printing techniques that is viewed highly as a viable tool for potential commercialization of the perovskite solar cells. Furthermore, a summary is given on green processing for the solution printing production of flexible perovskite devices.

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Non-fullerene small molecule electron acceptors for high-performance organic solar cells Hao Lin, Qiang Wang 2018, 27(4): 990-1016.  DOI: 10.1016/j.jechem.2017.11.028 摘要 ( 1411 )   Fullerenes and their derivatives are important types of electron acceptor materials and play a vital role in organic solar cell devices. However, the fullerene acceptor material has some difficulties to overcome the intrinsic shortcomings, such as weak absorption in the visible range, difficulty in modification and high cost, which limit the performance of the device and the large-scale application of this type of acceptors. In recent years, non-fullerene electron acceptor material has attracted the attention of scientists due to the advantages of adjustable energy level, wide absorption, simple synthesis, low processing cost and good solubility. Researchers can use the rich chemical means to design and synthesize organic small molecules and their oligomers with specific aggregation morphology and excellent optoelectronic properties. Great advances in the field of synthesis, device engineering, and device physics of non-fullerene acceptors have been achieved in the last few years. At present, non-fullerene small molecules based photovoltaic devices achieve the highest efficiency more than 13% and the efficiency gap between fullerenetype and non-fullerene-type photovoltaic devices is gradually narrowing. In this review, we explore recent progress of non-fullerene small molecule electron acceptors that have been developed and led to highefficiency photovoltaic devices and put forward the prospect of development in the future.

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Cation engineering on lead iodide perovskites for stable and high-performance photovoltaic applications Jue Gong, Peijun Guo, Savannah E. Benjamin, P. Gregory Van Patten, Richard D. Schaller, Tao Xu 2018, 27(4): 1017-1039.  DOI: 10.1016/j.jechem.2017.12.005 摘要 ( 1683 )   Perovskite solar cells (PSCs) based on methylammonium lead iodide (CH3NH3PbI3) have shown unprecedentedly outstanding performance in the recent years. Nevertheless, due to the weak interaction between polar CH3NH3+ (MA+) and inorganic PbI3- sublattices, CH3NH3PbI3 dramatically suffers from poor moisture stability, thermal decomposition and device hysteresis. As such, strong electrostatic interactions between cations and anionic frameworks are desired for synergistic improvements of the abovementioned issues. While replacements of I- with Br- and/or Cl- evidently widen optical bandgaps of perovskite materials, compositional modifications can solely be applied on cation components in order to preserve the broad absorption of solar spectrum. Herein, we review the current successful practices in achieving efficient, stable and minimally hysteretic PSCs with lead iodide perovskite systems that employ photoactive cesium lead iodide (CsPbI3), formamidinium lead iodide (HC(NH2)2PbI3, or FAPbI3), MA1-x-y-zFAxCsyRbzPbI3 mixed-cation settings as well as two-dimensional butylammonium (C4H9NH3+, or BA+)/MA+, polymeric ammonium (PEI+)/MA+ co-cation layered structures. Fundamental aspects behind the stabilization of perovskite phases α-CsPbI3, α-FAPbI3, mixed-cation MA1-x-y-zFAxCsyRbzPbI3 and crystallographic alignment of (BA)2(MA)3Pb4I13 for effective light absorption and charge transport will be discussed. This review will contribute to the continuous development of photovoltaic technology based on PSCs.

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Path towards high-efficient kesterite solar cells Dongxiao Wang, Wangen Zhao, Yi Zhang, Shengzhong(Frank) Liu 2018, 27(4): 1040-1053.  DOI: 10.1016/j.jechem.2017.10.027 摘要 ( 1736 )   Kesterite structure semiconductor Cu2ZnSn(S,Se)4 is one of the most promising candidate as a light absorber material to overtake the next generation of thin film solar cells, owing to its low cost, non-toxic, and earth abundant source materials. The Shockley-Queisser limit of the single junction Cu2ZnSn(S,Se)4 solar cell is over 30%, signifying a large potential of this family of solar cells. In the past years, with the development of synthesis techniques, Cu2ZnSn(S,Se)4 solar cells have attracted considerable attention and the power conversion efficiency of Cu2ZnSn(S,Se)4 solar cell has experienced a rapid progress. Presently, the certified champion efficiency of CZTSSe solar cells has reached to 12.6%, which is far below the efficiency of Cu(In,Ga)Se2 solar cell. In this review, the developments of Cu2ZnSn(S,Se)4 solar cells in recent years are briefly reviewed. Then the fundamental understanding of Cu2ZnSn(S,Se)4 solar cells is introduced, including materials and device structure, as well as the band alignment of hetero-junction and their impacts on device performance. After that, we mainly review the progress and achievements in the preparation processes, through vacuum and non-vacuum based processes. Finally, we outline the challenges and perspectives of this promising solar cell.

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A brief review on the lead element substitution in perovskite solar cells Chong Liu, Wenzhe Li, Jiandong Fan, Yaohua Mai 2018, 27(4): 1054-1066.  DOI: 10.1016/j.jechem.2017.10.028 摘要 ( 1575 )   Organic-inorganic halide perovskites have attracted huge attentions as the novel photoelectric function materials. So far, perovskite solar cells (PSCs) with prominent performance are still based on the lead halide perovskites, although they are potentially highly toxic. The issue of toxicity has become one of most crucial problems before its commercialization. Therefore, an increasing number of studies have focused on the lead element substitution in PSCs, and many excellent achievements have been reported. Alternative elements, e.g., Sn, Ge, Bi and Sb were successively used to fabricate lead-free perovskites, which provided potential possibility to tackle the toxicity issue. Recently, Sn-Pb hybrid perovskites were demonstrated to realize lead reduction without sacrificing the PCE. In addition, a new family of halide double-perovskites was explored and given high expectations. Here, we give a brief review on the lead substitution in PSCs, including theoretical explorations and experimental achievements, and finally we propose some perspectives.

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Research progress on silicon/carbon composite anode materials for lithium-ion battery Xiaohui Shen, Zhanyuan Tian, Ruijuan Fan, Le Shao, Dapeng Zhang, Guolin Cao, Liang Kou, Yangzhi Bai 2018, 27(4): 1067-1090.  DOI: 10.1016/j.jechem.2017.12.012 摘要 ( 1450 )   Silicon (Si) has been considered as one of the most promising anode material for the next generation lithium-ion batteries (LIBs) with high energy densities, due to its high theoretical capacity, abundant availability and environmental friendliness. However, silicon materials with low intrinsic electric and ionic conductivity suffer from huge volume variation during lithiation/delithiation processes leading to the pulverization of Si and subsequently resulting in severe capacity fading of the electrodes. Coupling of Si with carbon (C) realizes a favorable combination of the two materials properties, such as high lithiation capacity of Si and excellent mechanical and conductive properties of C, making silicon/carbon composite (Si/C) ideal candidates for LIBs anodes. In this review, recent progresses of Si/C materials utilized in LIBs are summarized in terms of structural design principles, material synthesis methods, morphological characteristics and electrochemical performances by highlighting the material structures. The mechanisms behind the performance enhancement are also discussed. Moreover, other factors that affect the performance of Si/C anodes, such as prelithiation, electrolyte additives, and binders, are also discussed. We aim to present a full scope of the Si/C-based anodes, and help understand and design future structures of Si/C anodes in LIBs.

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Recent progress on low dimensional perovskite solar cells Lingfeng Chao, Ze Wang, Yingdong Xia, Yonghua Chen, Wei Huang 2018, 27(4): 1091-1100.  DOI: 10.1016/j.jechem.2017.10.013 摘要 ( 1539 )   Low dimensional perovskites have recently attracted much attention due to their vertical growth of crystalline orientation, excellent film morphology, and long-term humidity, light, and heat stability. However, low dimensional perovskites suffer from low power conversion efficiency (PCE) with respect to their three dimensional analogues. Therefore, it is imperative to find excellent low-dimensional perovskite materials for improving the PCE. Previous work has demonstrated that bulkier organic molecules, e.g., C6H5(CH2)2NH3+(PEA+), CH3(CH2)3NH3+(n-BA+, iso-BA+), C2H4NH3+, and polyethylenimine cations (PEI+), play an important role in the formation of low-dimensional perovskites. In this review, we review the recent development of low dimensional perovskites for solar cells application in terms of film preparation, photophysics, and stability of perovskites, as well as the related device structure and physics. We have also discussed the future development of low-dimensional perovskites from materials design, fabrication processes, and device structure.

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Scalable solution coating of the absorber for perovskite solar cells Mikas Remeika, Yabing Qi 2018, 27(4): 1101-1110.  DOI: 10.1016/j.jechem.2017.10.005 摘要 ( 1410 )   Perovskite-based solar cell technology has advanced significantly and the power conversion efficiencies are nowadays on par with commercialized photovoltaic technologies. To realize the potential of perovskite solar cells, the focus is now shifting to scalable fabrication technologies that will enable low-cost solution processing of perovskite solar cells over large areas and with high yields. This review article discusses the fundamental concerns that arise when transitioning from laboratory to large area solution coating, available scalable coating technologies, and their applicability to the fabrication of high-performance perovskite solar cells. We find that a significant amount of work has been done to test scalable coating technologies, but also that often the methods that led to highest-performing cells in the laboratory (e.g. antisolvent processing) show limited compatibility with scalable coating methods. To achieve a high-yield and low-cost process, development must emphasize a high degree of control provided by sequential conversion of perovskite films and engineering of additives that fine-tune coating properties of perovskite precursor inks.

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Solar energy conversion on g-C3N4 photocatalyst: Light harvesting, charge separation, and surface kinetics Mu Xiao, Bin Luo, Songcan Wang, Lianzhou Wang 2018, 27(4): 1111-1123.  DOI: 10.1016/j.jechem.2018.02.018 摘要 ( 1459 )   Photocatalysis, which utilizes solar energy to trigger chemical reactions, is one of the most desirable solar-energy-conversion approaches. Graphitic carbon nitride (g-C3N4), as an attractive metal-free photocatalyst, has drawn worldwide research interest in the area of solar energy conversion due to its easy synthesis, earth-abundant nature, physicochemical stability and visible-light-responsive properties. Over the past ten years, g-C3N4 based photocatalysts have experienced intensive exploration, and great progress has been achieved. However, the solar conversion efficiency is still far from industrial applications due to the wide bandgap, severe charge recombination, and lack of surface active sites. Many strategies have been proposed to enhance the light absorption, reduce the recombination of charge carriers and accelerate the surface kinetics. This work makes a crucial review about the main contributions of various strategies to the light harvesting, charge separation and surface kinetics of g-C3N4 photocatalyst. Furthermore, the evaluation measurements for the enhanced light harvesting, reduced charge recombination and accelerated surface kinetics will be discussed. In addition, this review proposes future trends to enhance the photocatalytic performance of g-C3N4 photocatalyst for the solar energy conversion.

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Recent developments in electrocatalysts and future prospects for oxygen reduction reaction in polymer electrolyte membrane fuel cells Maryam Kiani, Jie Zhang, Yan Luo, Chunping Jiang, Jinlong Fan, Gang Wang, Jinwei Chen, Ruilin Wang 2018, 27(4): 1124-1139.  DOI: 10.1016/j.jechem.2018.01.019 摘要 ( 1692 )   The main difficulty in the extensive commercial use of polymer electrolyte membrane fuel cells (PEMFCs) is the use of noble metals such as Pt-based electrocatalyst at the cathode, which is essential to ease the oxygen reduction reaction (ORR) in fuel cells (FCs). To eliminate the high loading of Pt-based electrocatalysts to minimize the cost, extensive study has been carried out over the previous decades on the non-noble metal catalysts. Development in enhancing the ORR performance of FCs is mainly due to the doped carbon materials, Fe and Co-based electrocatalysts, these materials could be considered as probable substitutes for Pt-based catalysts. But the stability of these non-noble metal electrocatalysts is low and the durability of these metals remains unclear. The three basic reasons of instability are:(i) oxidative occurrence by H2O2, (ii) leakage of the metal site and (iii) protonation by probable anion adsorption of the active site. Whereas leakage of the metal site has been almost solved, more work is required to understand and avoid losses from oxidative attack and protonation. The ORR performance such as stability tests are usually run at low current densities and the lifetime is much shorter than desired need. Therefore, improvement in the ORR activity and stability are the key issues of the non-noble metal electrocatalyst. Based on the consequences obtained in this area, numerous future research directions are projected and discussed in this paper. Hence, this review is focused on improvement of stability and durability of the non-noble metal electrocatalyst.

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First-principles study on the alkali chalcogenide secondary compounds in Cu(In,Ga)Se2 and Cu2ZnSn(S,Se)4 thin film solar cells Xian Zhang, Dan Han, Shiyou Chen, Chungang Duan, Junhao Chu 2018, 27(4): 1140-1150.  DOI: 10.1016/j.jechem.2017.11.024 摘要 ( 1377 )   The beneficial effect of the alkali metals such as Na and K on the Cu(In,Ga)Se2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTSSe) solar cells has been extensively investigated in the past two decades, however, in most of the studies the alkali metals were treated as dopants. Several recent studies have showed that the alkali metals may not only act as dopants but also form secondary phases in the absorber layer or on the surfaces of the films. Using the first-principles calculations, we screened out the most probable secondary phases of Na and K in CIGS and CZTSSe, and studied their electronic structures and optical properties. We found that all these alkali chalcogenide compounds have larger band gaps and lower VBM levels than CIGS and CZTSSe, because the existence of strong p-d coupling in CIS and CZTS pushes the valence band maximum (VBM) level up and reduces the band-gaps, while there is no such p-d coupling in these alkali chalcogenides. This band alignment repels the photo-generated holes from the secondary phases and prevents the electron-hole recombination. Moreover, the study on the optical properties of the secondary phases showed that the absorption coefficients of these alkali chalcogenides are much lower than those of CIGS and CZTSSe in the energy range of 0-3.4 eV, which means that the alkali chalcogenides may not influence the absorption of solar light. Since the alkali metal dopants can passivate the grain boundaries and increase the hole carrier concentration, and meanwhile their related secondary phases have innocuous effect on the optical absorption and band alignment, we can understand why the alkali metal dopants can improve the CIGS and CZTSSe solar cell performance.

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Optical simulation of external quantum efficiency spectra of CuIn1-xGaxSe2 solar cells from spectroscopic ellipsometry inputs Abdel-Rahman A. Ibdah, Prakash Koirala, Puruswottam Aryal, Puja Pradhan, Michael J. Heben, Nikolas J. Podraza, Sylvain Marsillac, Robert W. Collins 2018, 27(4): 1151-1169.  DOI: 10.1016/j.jechem.2017.10.029 摘要 ( 1387 )   Applications of in-situ and ex-situ spectroscopic ellipsometry (SE) are presented for the development of parametric expressions that define the real and imaginary parts (ε1, ε2) of the complex dielectric function spectra of thin film solar cell components. These spectra can then be utilized to analyze the structure of complete thin film solar cells. Optical and structural/compositional models of complete solar cells developed through least squares regression analysis of the SE data acquired for the complete cells enable simulations of external quantum efficiency (EQE) without the need for variable parameters. Such simulations can be compared directly with EQE measurements. From these comparisons, it becomes possible to understand in detail the origins of optical and electronic gains and losses in thin film photovoltaics (PV) technologies and, as a result, the underlying performance limitations. In fact, optical losses that occur when above-bandgap photons are not absorbed in the active layers can be distinguished from electronic losses when electron-hole pairs generated in the active layers are not collected. This overall methodology has been applied to copper indium-gallium diselenide (CuIn1-xGaxSe2; CIGS) solar cells, a key commercialized thin film PV technology. CIGS solar cells with both standard thickness (>2 μm) and thin (<1 μm) absorber layers are studied by applying SE to obtain inputs for EQE simulations and enabling comparisons of simulated and measured EQE spectra. SE data analysis is challenging for CIGS material components and solar cells because of the need to develop an appropriate (ε1, ε2) database for the CIGS alloys and to extract absorber layer Ga profiles for accurate structural/compositional models. For cells with standard thickness absorbers, excellent agreement is found between the simulated and measured EQE, the latter under the assumption of 100% collection from the active layers, which include the CIGS bulk and CIGS/CdS heterojunction interface layers. For cells with thin absorbers, however, an observed difference between the simulated and measured EQE can be attributed to losses via carrier recombination within a ~0.15 μm thickness of CIGS adjacent to the Mo back contact. By introducing a carrier collection probability profile into the simulation, much closer agreement is obtained between the simulated and measured EQE. In addition to the single spot capability demonstrated in this study, ex-situ SE can be applied as well to generate high resolution maps of thin film multilayer structure, component layer properties and their profiles, as well as short-circuit current density predictions. Such mapping is possible due to the high measurement speed of <1 s per (ψ,△) spectra achievable by the multichannel ellipsometer.

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Ultrafast selective extraction of hot holes from cesium lead iodide perovskite films Qing Shen, Teresa S. Ripolles, Jacky Even, Yaohong Zhang, Chao Ding, Feng Liu, Takuya Izuishi, Naoki Nakazawa, Taro Toyoda, Yuhei Ogomi, Shuzi Hayase 2018, 27(4): 1170-1174.  DOI: 10.1016/j.jechem.2018.01.006 摘要 ( 1736 )   Lead halide perovskites have some unique properties which are very promising for optoelectronic applications such as solar cells, LEDs and lasers. One important and expected application of perovskite halide semiconductors is solar cell operation including hot carriers. This advanced solar cell concept allows overcoming the Shockley-Queisser efficiency limit, thereby achieving energy conversion efficiency as high as 66% by extracting hot carriers. Understanding ultrafast photoexcited carrier dynamics and extraction in lead halide perovskites is crucial for these applications. Here, we clarify the hot carrier cooling and transfer dynamics in all-inorganic cesium lead iodide (CsPbI3) perovskite using transient absorption spectroscopy and Al2O3, poly(3-hexylthiophene-2,5-diyl) (P3HT) and TiO2 as selective contacts. We find that slow hot carrier cooling occurs on a timescale longer than 10 ps in the cases of CsPbI3/Al2O3 and CsPbI3/TiO2, which is attributed to hot phonon bottleneck for the high photoexcited carrier density. An efficient ultrafast hole transfer from CsPbI3 to the P3HT hole extracting layer is observed. These results suggest that hot holes can be extracted by appropriate selective contacts before energy dissipation into the halide perovskite lattice and that CsPbI3 has a potential for hot carrier solar cell applications.

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Diketopyrrolopyrrole based D-π-A-π-D type small organic molecules as hole transporting materials for perovskite solar cells Haoliang Cheng, Xiaojuan Zhao, Yan Shen, Mingkui Wang, Lingyun Wang, Herbert Meier, Derong Cao 2018, 27(4): 1175-1182.  DOI: 10.1016/j.jechem.2017.08.007 摘要 ( 1739 )   Three novel diketopyrrolopyrrole (DPP) based small organic molecules were synthesized as hole transporting materials for perovskite solar cells. The effects of different donors and π bridges on the performance of perovskite solar cells (PSCs) were discussed. The efficiency of TPADPP-1, TPADPP-2, PTZDPP-2 was 5.10%, 9.85% and 8.16% respectively. Compared to TPADPP-2, the voltage of PTZDPP-2 was higher. Because the electron-donating ability of phenothiazine based donor was larger than that of triphenylamine based donor, the HOMO level of PTZDPP-2 was lower than that of TPADPP-2. The results indicated that the diketopyrrolopyrrole based D-π-A-π-D type small organic molecule might be a promising hole transporting material in the perovskite solar cells.

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Intensification of photocatalytic decomposition of water by ultrasound Arvind Singh, A. S. K. Sinha 2018, 27(4): 1183-1188.  DOI: 10.1016/j.jechem.2017.08.001 摘要 ( 1492 )   Photocatalysis of water with and without ultrasound was studied using rGO supported CdS catalyst utilizing visible light. A higher hydrogen production was observed when ultrasound was used. This is attributed to a faster removal of bubbles of hydrogen from the surface of photocatalyst due to the mechanical energy associated with ultrasound overcoming surface tension. It has been further reported that the rate of hydrogen production decreased with time due to reversible deactivation of catalyst. This has been attributed to decrease in rate of hydrogen desorption with time.

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Facile fabrication of amphoteric semi-interpenetrating network membranes for vanadium flow battery applications Ruijun Gan, Yanjiao Ma, Shanshan Li, Fengxiang Zhang, Gaohong He 2018, 27(4): 1189-1197.  DOI: 10.1016/j.jechem.2017.09.017 摘要 ( 1347 )   For improvement of vanadium redox flow battery (VRB) performance, novel amphoteric semiinterpenetrating membranes (ASIPN) were prepared using poly(ether ether ketone) (PEEK) and polysulfone (PSf), the former bearing sulfonic groups and the latter imidazolium. These two groups form ionic crosslinks between PEEK and PSf; meanwhile, covalent cross links were built between PSf chains with addition of N-(3-aminopropyl)-imidazole. The amphoteric nature of the membrane allows facile proton and anion transport; the IPN structure and the presence of imidazolium cation effectively suppress vanadium ion crossover through the membrane. Therefore, the ASIPN based VRBs show higher Coulombic efficiency and energy efficiency than that assembled with pristine SPEEK and Nafion 212 membranes. Our work demonstrates that the ASIPN membranes are promising for VRB applications.

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Rheological properties and viscosity reduction of South China Sea crude oil Hui Sun, Xingxing Lei, Benxian Shen, Huiran Zhang, Jichang Liu, Gengnan Li, Di Wu 2018, 27(4): 1198-1207.  DOI: 10.1016/j.jechem.2017.07.023 摘要 ( 1661 )   The rheological properties of South China Sea (SCS) crude oil were studied. A group of synthetic long-chain polymers, including octadecyl acrylate-maleic anhydride bidodecyl amide copolymer (VR-D), octadecyl acrylate-maleic anhydride bioctadecyl amide copolymer (VR-O) and octadecyl acrylate-maleic anhydride phenly amide copolymer (VR-A), were employed to serve as viscosity reducers (VRs). Their performance was evaluated by both experimental and computational methodologies. The results suggest that the SCS crude oil has low wax content yet high resin and asphaltene contents, which lead to high viscosity through formation of association structures. Additionally, the SCS crude oil appears to be a pseudoplastic fluid showing linear shear stress-shear rate dependence at low temperature. Interestingly, it gradually evolves into a Newtonian fluid with exponential relationship between shear stress and shear rate at higher temperature. Synthetic VRs demonstrate desirable and effective performance on improvement of the rheological properties of SCS crude oil. Upon the introduction of 1000 ppm VR-O, which is synthesized by using octadecylamine in the aminolysis reaction, the viscosity of SCS crude oil is decreased by 44.2% at 15℃ and 40.2% at 40℃. The computational study suggests significant energy level increase and shear stress decrease for VR-containing crude oil systems.

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Facile synthesis of MoS2/graphite intercalated composite with enhanced electrochemical performance for sodium ion battery Qingqing Yang, Maocheng Liu, Yumei Hu, Yan Xu, Lingbin Kong, Long Kang 2018, 27(4): 1208-1213.  DOI: 10.1016/j.jechem.2017.08.009 摘要 ( 1510 )   MoS2 is a promising anode material for sodium ion batteries owing to its two-dimensional layered structure and high specific capacity. But it still exhibits a poor cycle stability and limited rate capability for Na+ storage because of its poor electrical conductivity and structural instability. In this work, MoS2/graphite composite is fabricated by mechanically delaminated and restacked MoS2 and graphite to form two-dimensional composite layers. The graphite sheets will improve electrical conductivity and prevent the aggregation as well as structure collapse of the MoS2 layers during charge-discharge process. The MoS2/graphite composite exhibits excellent Na+ storage properties. It delivers a high discharge specific capacity of 358.2 mAh/g at a current density of 100 mA/g in the first discharge process and with capacity retention of 68.1% after 800 cycles (retains 244 mAh/g). The average discharge specific capacities retain 250.9 and 225.4 mAh/g corresponding to the current densities of 100 and 1000 mA/g, showing excellent rate capability. The improved electrochemical performance is attributed to the improved electrical conductivity and structural stability after composition of graphite sheets. The study demonstrates a new research strategy for improving sodium ion storage properties of MoS2.

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200-nm long TiO2 nanorod arrays for efficient solid-state PbS quantum dot-sensitized solar cells Zhengguo Zhang, Chengwu Shi, Kai Lv, Chengfeng Ma, Guannan Xiao, Lingling Ni 2018, 27(4): 1214-1218.  DOI: 10.1016/j.jechem.2017.08.017 摘要 ( 1400 )   To ensure the infiltration of spiro-OMeTAD into the quantum dot-sensitized photoanode and to consider the limit of the hole diffusion length in the spiro-OMeTAD layer, a rutile TiO2 nanorod array with a length of 200 nm, a diameter of 20 nm and an areal density of 720 μm-2 was successfully prepared using a hydrothermal method with an aqueous-grown solution of 38 mM titanium isopropoxide and 6 M hydrochloric acid at 170℃ for 75 min. PbS quantum dots were deposited by a spin coating-assisted successive ionic layer adsorption and reaction (spin-SILAR), and all solid-state PbS quantum dot-sensitized TiO2 nanorod array solar cells were fabricated using spiro-OMeTAD as electrolytes. The results revealed that the average crystal size of PbS quantum dots was ~7.8 nm using Pb(NO3)2 as the lead source and remain unchanged with the increase of the number of spin-SILAR cycles. The all solid-state PbS quantum dot-sensitized TiO2 nanorod array solar cells with spin-SILAR cycle numbers of 20, 30 and 40 achieved the photoelectric conversion efficiencies of 3.74%, 4.12% and 3.11%, respectively, under AM 1.5 G illumination (100 mW/cm2).

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Synergistic interaction between redox-active electrolytes and functionalized carbon in increasing the performance of electric double-layer capacitors Guoxiang Wang, Mingyuan Zhang, Hongfeng Xu, Lu Lu, Zuoyi Xiao, Sa Liu 2018, 27(4): 1219-1224.  DOI: 10.1016/j.jechem.2017.08.020 摘要 ( 1518 )   The increasing demand of high-performance supercapacitors has aroused great interest in developing specific capacitance and energy density. Active carbon (AC) has attracted much attention as a promising electrode material for electric double-layer capacitors (EDLCs). Here, a facile strategy has been employed to fabricate high-performance EDLCs using the surface-oxygen functionalized active carbon (FAC) as an electrode and 2 M KOH with K3Fe(CN)6 as an electrolyte. In this system, K3Fe(CN)6 was used as a redox additive to enhance the performance of EDLCs. A 38.5% increase in specific capacitance (207.7 F g-1) was achieved compared with the KOH electrolyte without adding K3Fe(CN)6 (152.9 F g-1), due to the synergistic effects between oxygenic functional groups and redox electrolyte. These findings provide an alternative route to improve the performance of EDLCs, which are promising candidates for the broad applications of high-performance supercapacitors.

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Fluoride-mediated nano-sized high-silica ZSM-5 as an ultrastable catalyst for methanol conversion to propylene Junjie Li, Min Liu, Xinwen Guo, Chengyi Dai, Chunshan Song 2018, 27(4): 1225-1230.  DOI: 10.1016/j.jechem.2017.08.018 摘要 ( 1528 )   Fluoride mediated nano-sized ZSM-5 (ZSM-5-F) with a high Si/Al ratio of 181 was fabricated using a seed-induction method and evaluated the catalysis of the methanol to propylene (MTP) reaction. High propylene selectivity (45%) was similar to ZSM-5-OH synthesized via a hydroxide route. However, ZSM-5-F showed much longer lifetime (305 h) compared with ZSM-5-OH (157 h) in spite of similar crystal size and aluminum content. Characterization by NH3-TPD, Py-IR, OH-IR, SEM, TG-DTA, XRD and 1H MAS NMR techniques indicated that the enhanced catalytic performance of ZSM-5-F is attributed to the fewer structural defects in the form of internal silanol groups and silanol nests.

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Regeneration behavior of tin oxide sorbent for warm syngas desulfurization Yi Yang, Yixiang Shi, Ningsheng Cai 2018, 27(4): 1231-1238.  DOI: 10.1016/j.jechem.2017.08.019 摘要 ( 1479 )   The steam regeneration and SO2 regeneration of tin oxide for warm syngas desulfurization is studied in the temperature range of 400-600℃. In the steam regeneration, reversible removal of H2S achieved. Regenerated H2S concentration increased with the increasing regeneration temperature. SnO2 sorbent can achieve a complete regeneration by steam at 500 and 600℃. In the SO2 regeneration, elemental sulfur was produced by the reaction of SnS and SO2. Raising the regeneration temperature (500-600℃) or SO2 concentration (1.5-10 vol%) improved the regeneration rate. Under SO2 regeneration at 500℃, SnS2 formed in the sorbent due to the interconversion of tin sulfides. Under steam regeneration or SO2 regeneration, the cyclic breakthrough sulfur capacity of SnO2 sorbent decreased because of the sintering caused by low melting component SnS. A two-stage regeneration process was applied to recover the elemental sulfur which achieved a complete regeneration.

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Improved electrochemical performances of yttrium oxyfluoride-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 for lithium ion batteries Yaxin Hao, Fangning Yang, Didi Luo, Jianhua Tian, Zhongqiang Shan 2018, 27(4): 1239-1246.  DOI: 10.1016/j.jechem.2017.09.024 摘要 ( 1323 )   The Li-rich layered oxides show a higher discharge capacity over 250 mAh/g and have been developed into a promising positive material for lithium ion batteries. A rare earth metal oxyfluoride YOF-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 composites have been synthesized by a simple wet chemical method. Crystal structure, micro-morphology and element valence of the pristine and YOF-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 materials are characterized by XRD, SEM, TEM, and XPS. The results indicate that all materials exhibit a typical layered structure, and are made up of small and homogenous particles ranging from 100 nm to 200 nm. In addition, YOF layer with a thickness of approximately 3-8 nm is precisely coated on the surface of the Li[Li0.2Mn0.54Ni0.13Co0.13]O2. Constant current charge/discharge tests at various current densities show that the electrochemical performance of 2 wt% YOF-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 has been improved significantly. 2 wt% YOF-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 delivers the highest discharge capacity of 250.4 mAh/g at 20 mA/g among all the samples, and capacity retention of 87% after 100 charge/discharge cycles at 200 mA/g while that of the pristine one is only 81.6%. The superior electrochemical performance of 2wt% YOF-coated sample is ascribed to YOF coating layer, which could not only reduce side reactions between the electrode and liquid electrolyte, but also promote lithium ion migration.

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Sulfonated fluorinated multi-block copolymer hybrid containing sulfonated(poly ether ether ketone) and graphene oxide: A ternary hybrid membrane architecture for electrolyte applications in proton exchange membrane fuel cells Ae Rhan Kim, Mohanraj Vinothkannan, Dong Jin Yoo 2018, 27(4): 1247-1260.  DOI: 10.1016/j.jechem.2018.02.020 摘要 ( 1449 )   A ternary hybrid membrane architecture consisting of sulfonated fluorinated multi-block copolymer (SFMC), sulfonated (poly ether ether ketone) (SPEEK) and 1 or 5 wt% graphene oxide (GO) was fabricated through a facile solution casting approach. The simple, but effective monomer sulfonation was performed for SFMC to create compact and rigid hydrophobic backbone structures, while conventional random sulfonation was carried-out for SPEEK. Hydrophilic-hydrophobic-hydrophilic structure of SFMC enhances the compatibility with SPEEK and GO and allows for an unprecedented approach to alter mechanical strength and proton conductivity of ternary hybrid membrane, as verified from universal test machine (UTM) curves and alternating current (AC) impedance plots. The impact of GO integration on the morphology and roughness of hybrid membrane was scrutinized using field emission scanning electron microscope (FE-SEM) and atomic force microscope (AFM). Ternary hybrid showed uniform intercalation of GO nanosheets throughout the entire surface of membrane with an increased surface roughness of 8.91 nm. The constructed ternary hybrid membrane revealed excellent water absorption, ion exchange capacity and gas barrier properties, while retaining reasonable dimensional stability. The well-optimized ternary hybrid membrane containing 5 wt% GO revealed a maximum proton conductivity of 111.9 mS/cm, which is higher by a factor of two-fold with respect to that of bare SFMC membrane. The maximum PEMFC power density of 528.07 mW/cm2 was yielded by ternary hybrid membrane at a load current density of 1321.1 mA/cm2 when operating the cell at 70℃ under 100% relative humidity (RH). In comparison, a maximum power density of only 182.06 mW/cm2 was exhibited by the bare SFMC membrane at a load current density of 455.56 mA/cm2 under same operating conditions.

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Co NP/NC hollow nanoparticles derived from yolk-shell structured ZIFs@polydopamine as bifunctional electrocatalysts for water oxidation and oxygen reduction reactions Jiao Zhao, Feng Rong, Yi Yao, Wenjun Fan, Mingrun Li, Qihua Yang 2018, 27(4): 1261-1267.  DOI: 10.1016/j.jechem.2018.04.015 摘要 ( 1482 )   The pyrolysis under inert atmosphere has been widely used for the synthesis of metal containing heteroatoms doped carbon materials, versatile catalysts for various reactions. However, it is difficult to prevent metal nanoparticles aggregation during pyrolysis process. Herein, we reported the efficient synthesis of nitrogen doped carbon hollow nanospheres with cobalt nanoparticles (Co NP, ca. 10 nm in size) distributed uniformly in the shell via pyrolysis of yolk-shell structured Zn-Co-ZIFs@polydopamine (PDA). PDA acted as both protection layer and carbon source, which successfully prevented the aggregation of cobalt nanoparticles during high-temperature pyrolysis process. The Co NP and N containing carbon (Co NP/NC) hollow nanospheres were active for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), affording overpotential of 430 mV at 10 mA/cm2 for OER in 1 M KOH and comparable half-wave potential to that of Pt/C (0.80 V vs RHE) for ORR in 0.1 M KOH. The superior performance of carbon hollow nanospheres for both OER and ORR was mainly attributed to its small metal nanoparticles, N-doping and hollow nanostructure. The protection and confinement effect that originated from PDA coating strategy could be extended to the synthesis of other hollow structured carbon materials, especially the ones with small metal nanoparticles.