Renewable Energy Global Innovations features: One-pot synthesis of hierarchical MnO2-modified diatomites for electrochemical capacitor electrodes

Significance Statement

The hierarchical and porous MnO₂-modified diatomite structures are prepared for the first time by a one pot hydrothermal method. We also demonstrate the synthesis of size- and shape-controlled MnO₂ nanostructures by replica molding from diatom silica structures for high-performance supercapacitors. The results show that birnessite-type MnO₂ nanosheets are observed to grow vertically on the purified diatomite, thus building hierarchical architecture. Three types of hierarchical hollow MnO₂ patterns with different three-dimensional (3D) structures, shapes and large surface areas were successfully prepared from three diatom species by a template-assisted hydrothermal process. The extraordinary precision and nano-scale resolution of 3D replications of complex biological architecture from diatoms to artificial MnO₂ structures are confirmed. The electrochemical results demonstrate that the MnO₂-modified diatomite electrode exhibits highly reversible features, good rate abilities, and good cycle stability (95.92% over 5000 cycles) demonstrating the suitability of the low-cost MnO₂-modified diatomite structure as a potential electrode material for supercapacitors. 

About The Author

Dr. Yu Xin Zhang received his B. Eng. and M. Eng. in Chemical Engineering from Tianjin University in 2000 and 2003, respectively. He received his Ph.D degree in Chemical and Biomolecular Engineering from the National University of Singapore (NUS) in 2008, and continued to work as a research fellow in Prof. Hua Chun Zeng’s group at NUS till 2009. Now Dr. Zhang is a full professor of College of Materials Science and Engineering in Chongqing University. Dr. Zhang’s research interest is self-assembled nanostructures for energy storage materials and photocatalysts. 

Journal Reference

Journal of Power Sources. Volume 246, 2014, Pages 449-456.

Yu Xin Zhang ^1,2,*, Ming Huang¹, Fei Li¹ , their collaborators

Show Affiliations

1. College of Material Science and Engineering, Chongqing University, Chongqing 400044, P.R. China

2. National Key Laboratory of Fundamental Science of Micro/Nano-Devices and System Technology, Chongqing University, Chongqing 400044, P.R. China

Abstract

The hierarchical and porous MnO₂-modified diatomite structures are prepared for the first time by a one-pot hydrothermal method. The morphology and structure of MnO₂-modified diatomite hierarchical structures are examined by focus ion beam scanning electron microscopy (FIB/SEM) and X-ray diffraction spectroscopy (XRD). The results show that Birnessite-type MnO₂ nanosheets are observed to grow vertically on the purified diatomite, thus building hierarchical architecture. Furthermore, the electrochemical properties of the MnO₂-modified diatomite electrodes are elucidated by cyclic voltammograms, galvanostatic charge/discharge tests and electrochemical impedance spectroscopy in 1 M Na₂SO₄ electrolyte. The electrochemical results demonstrate that the MnO₂-modified diatomite electrode exhibits highly reversible features and good rate abilities, respectively. Significantly, it exhibits the specific capacitance of 202.6 F g^-1 for the MnO₂-modified diatomite and 297.8 F g^-1 for the MnO₂ nanostructures after etching the diatomite. The capacitance retention of 95.92% over 5000 cycles further indicates the suitability of the low-cost MnO₂-modified diatomite structure as a potential electrode material for supercapacitors.

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Renewable Energy Global Innovations features: Self-Assembly of Mesoporous Nanotubes Assembled from Interwoven Ultrathin Birnessite-type MnO2 Nanosheets for Asymmetric Supercapacitors

Significance Statement

 Here, we develop a simple and cost-effective approach to prepare CuO@MnO₂ core-shell nanostructures without any surfactants and ultrathin MnO₂ nanosheets-built nanotubes have been fabricated via a large-scale chemical etching method. An asymmetric supercapacitor with CuO@MnO₂ core-shell nanostructure as the positive electrode and activated microwave exfoliated graphite oxide (MEGO) as the negative electrode yields an energy density of 22.1 Wh kg^-1 and a maximum power density of 85.6 kW kg^-1; the device shows a long-term cycling stability which retains 101.5% of its initial capacitance even after 10000 cycles. The MnO₂ nanotubes in a three-electrode system display much high specific capacitance (377.5 F g^-1 at current density of 0.25 A g^-1), good rate performance.

Moreover, an asymmetric supercapacitor on the basis of MnO₂ nanotubes as the positive electrode and activated graphenes (AG) as the negative electrode produced an energy density of 22.68 Wh kg^-1 and a maximum power density of 4.5 kW kg^-1. Such a facile strategy to fabricate the hierarchical CuO@MnO2 core-shell nanostructure and MnO₂ nanotubes with significantly improved functionalities opens up a novel avenue to design electrode materials on demand for high-performance supercapacitor applications. 

About The Author

Dr. Yu Xin Zhang received his B. Eng. and M. Eng. in Chemical Engineering from Tianjin University in 2000 and 2003, respectively. He received his Ph.D degree in Chemical and Biomolecular Engineering from the National University of Singapore (NUS) in 2008, and continued to work as a research fellow in Prof. Hua Chun Zeng’s group at NUS till 2009. Now Dr. Zhang is a full professor of College of Materials Science and Engineering in Chongqing University. Dr. Zhang’s research interest is self-assembled nanostructures for energy storage materials and photocatalysts. 

Journal Reference

Scientific Reports. Volume 4:4518, 2014.

Ming Huang¹, Yuxin Zhang^1,2, Fei Li¹, Lili Zhang³, Rodney S. Ruoff⁴, Zhiyu Wen² , Qing Liu¹

Show Affiliations

1. College of Materials Science and Engineering, Chongqing University, Chongqing 400044, P.R. China,

2. National Key Laboratory of Fundamental Science of Micro/Nano-Devices and System Technology, Chongqing University, Chongqing 400044, P.R. China,

3. Institute of Chemical and Engineering Sciences, A*STAR, 1 Pesek Road, Jurong Island 627833, Singapore, Department of
4. Mechanical Engineering and the Materials Science and Engineering Program, The University of Texas at Austin, One University Station C2200, Austin, Texas 78712, United States.

Abstract

Porous nanotubes comprised of MnO2 nanosheets were fabricated with a one-pot hydrothermal method using polycarbonate membrane as the template. The diameter and thickness of nanotubes can be controlled by choice of the membrane pore size and the chemistry. The porous MnO2 nanotubes were used as a supercapacitor electrode. The specific capacitance in a three-electrode system was 365 F g21 at a current density of 0.25 A g21 with capacitance retention of 90.4% after 3000 cycles. An asymmetric supercapacitor with porous MnO2 nanotubes as the positive electrode and activated graphene as the negative electrode yielded an energy density of 22.5 Wh kg21 and a maximum power density of 146.2 kW kg21; these values exceeded those reported for other MnO2 nanostructures. The supercapacitor performance was correlated with the hierarchical structure of the porous MnO2 nanotubes.

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Renewable Energy Global Innovations features: Optimization of the CeO2/CeCl3 cycle by cerium IV oxide reductive dissolution catalysis

Journal Reference

International Journal of Hydrogen Energy, Volume 40, Issue 39, 2015, Pages 13272–13280. 

Florent Lemont, Alisée Barbier, Samuel Resin

Commissariat à l’Energie Atomique (French Atomic Energy Commission) – DEN/DTCD/SCDV/LPIC, France

Abstract

While thermochemical cycles can be a way to produce hydrogen, physiochemical studies show that implementing them is often difficult for reactivity reasons. Most of the cycles actually involve solid–gas type systems with limited reactivity due to interface passivation processes. To overcome this difficulty, studies have shown that using the CeO₂/CeCl₃ pair, in which the cerium undergoes a reversible oxidation–reduction cycle, has enormous potential since it may partially be carried out in aqueous phase by reductive dissolution from cerium oxides (IV) to cerium chloride (III).

If the first reaction of the cycle is well known for industrial application, its second and its third reaction still need some investigation. Thus, this article primarily describes the work done on the second reaction to assess the possibility of carrying out cerium reduction in aqueous phase. The extremely positive results have highlighted the possibility of achieving 100% reaction efficiency in systems catalyzed by fluoride ions. Conducting the reaction with in-line distillation of the excess water also helps significantly reduce reaction time which offers good potential for the next stage. A ratio of 8 ml of a 20 w% HCl solution per gram of CeO₂ containing 6w% of CaF₂ leads to ensure a total reaction in a few minutes at 108.6 °C (boiling temperature of the H₂O–HCl azeotrope).

The work presented herein also describes a brief feasibility study for the third reaction cycle which could be carried out by spraying the solution from the second reaction, in a hot column whose temperature will be determined by further work. These results have allowed upgrading the first flowsheet proposed in a previous publication.

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Renewable Energy Global Innovations features: Performance of mixed LED light wavelengths on biogas upgrade and biogas fluid removal by microalga Chlorella sp.

Significance Statement

Biogas is the most important renewable energy resource that attracts attention all around the world. In Europe, the biogas production increases from 1.18 million MMBtu d^-1 in 2010 to 1.46 million MMBtu d^-1 in 2013, while the total biogas potential is estimated as 16 million MMBtu d^-1. In China, the biogas production of small scale projects raises from 180 million m³ in 1996 to 1000 m³ in 2007, and the medium and large scale biogas projects raises from 12 billion m³ in 1996 to 600 billion m³ in 2007.

Raw biogas usually consists of methane (CH₄, approximately 60 vol. %), carbon dioxide (CO₂, approximately 40 vol. %), and other trace compositions including hydrogen sulfide (H₂S), water vapor, etc. However, the relatively high concentration of CO₂ in raw biogas will lower its heat content as well as increase its energy demand of compression and transportation usage. The biogas upgrading is removing CO₂ from raw biogas. It is the precondition for biogas high efficient usage. When the CO₂ content in the biogas is decreased, the CH₄ concentration in the biogas is increased. The biogas CH₄ concentration should be upgraded to at least higher than 90% (vol. %) to meet the criterion for using as fuel for vehicles or even substitute for natural gas.

There are several biogas upgrading techniques that have been widely applied nowadays, including absorption of liquids with physics/chemical adsorbent, membranes separation, pressure swing adsorption, and cryogenic separation. However, they usually need high capital cost when build construction and consume a large amount of energy during treating process. This makes above mentioned techniques achieve high economic benefit only when they are used in large-scale industrial biogas projects. Most of these techniques also require complicated operating systems, and produce unwanted end products that need further treatment or result in secondary pollution. Further, the CO₂, which removed from the raw biogas, is always discharged into the atmosphere as greenhouse gas in these techniques. In addition, most physical/chemical technologies for CO₂ removal require a prior removal of H₂S.

An alternative technique to upgrade biogas is to use photosynthetic CO₂ uptake by microalgae. Microalgae have high carbon fixation ability and rapid growth rate, and can be adapted to various environmental conditions. When microalgae are utilized for biogas upgrading, the photosynthesis can efficiently convert CO₂ in raw biogas into its biomass. This allows the valorization of biogas CO₂ in the form of a valuable microalgae biomass, which can be used as feedstock to produce biofuels or even high value-added by-product. Anaerobic digestion not only produce raw biogas, but also nutrient-rich waste stream, called biogas slurry, which can be uptake freely during microalgae growth process and made the major contribution to the nitrogen and phosphorus removal from biogas slurry wastewater. Therefore, removing CO₂ from raw biogas by culturing microalgae with biogas slurry is a highly potential technique for simultaneous biogas upgrading and biogas slurry decontamination.

However, as far as we know, there is a little literature available about the simultaneously biogas upgrading and biogas slurry decontamination by using of the photosynthetic CO₂ uptake of microalgae, particularly about its effects under various light intensities and wavelengths. Therefore, this research focused on the effects of various LED artificial light source’s light wavelengths, light intensities, and photoperiods on biogas upgrading and simultaneously biogas slurry decontamination by using of microalgae photo bioreactor. Furthermore, the most appropriate light wavelength was discussed. The lighting control strategy was also optimized by analyzing the microalgae growth, as well as the efficiencies of biogas CO₂ removal and simultaneously biogas slurry decontamination under various light intensities and photoperiod’s treatments.

About The Author

Associate professor Dr. Cheng YAN comes from the Department of Environmental Science and Engineering, School of Environmental Studies, China University of Geosciences (Wuhan), No. 388 Lumo Road, Hongshan District, Wuhan 430074, Hubei Province, PR China.

Dr. Cheng YAN focused on Bioenergy with Carbon Capture and Storage (BECCS). He developed several Negative Emission Technologies (NETs), which involve CO₂ capture by biological processes from diffuse and point sources, atmospheric CO₂ capture by microalgae, microalgae as bio-agent for CO₂ mitigation, and CO₂ emission valorization. He also pays close attention to optimizing microalgae photo-bioreactor with artificial lighting system, and upgrading biogas by microalgae system. The research field about purifying anaerobic fermentation slurry by microalgae is also interested.

Dr. Cheng YAN has already published 17 academic papers (10 as the first author, 1 as the second author, and other 6 as cooperator) in refereed international JCR publications in English. He is keen on academic exchanges and participated in several academic international conferences in Barcelona, Prague, Dublin, and Singapore.

Journal Reference

Applied Energy, Volume 178, 15 September 2016, Pages 9–18. 

Cheng Yan^1,2, Liandong Zhu³, Yanxin Wang²

Show Affiliations

1. Laboratory of Basin Hydrology and Wetland Eco-restoration, China University of Geosciences (Wuhan), Wuhan 430074, China
2. Department of Environmental Science and Engineering, School of Environmental Studies, China University of Geosciences (Wuhan), Wuhan 430074, China
3. Faculty of Technology, University of Vaasa, FI65101 Vaasa, Finland

 

Abstract

Anaerobic digestion not only produces raw biogas which needs to be upgraded, but also nutrient-rich waste stream biogas slurry which needs decontamination. Therefore, this research focused on the effects of various light wavelengths, light intensities, and photoperiods on biogas upgrading and simultaneously biogas slurry decontamination by using of microalgae photobioreactor. The microalgae photobioreactor was a transparent polyethylene bag (80 cm × 60 cm × 11 cm). The results demonstrated that biogas upgrading and simultaneously biogas slurry decontamination was successfully achieved by the use of the photosynthetic CO₂ uptake by microalgae photobioreactor. The optimal light wavelength was the mixed LED red:blue = 5:5; whereas the optimized lighting control strategy was: low light intensity (300 μmol m⁻² s⁻¹) with long photoperiod (16 h light:8 h dark) for the time course of 0–48 h, moderate light intensity (600 μmol m⁻² s⁻¹) with middle photoperiod (14 h light:10 h dark) for the time course of 48–96 h, and high light intensity (900 μmol m⁻² s⁻¹) with short photoperiod (12 h light:12 h dark) for the time course of 96–144 h. Its biogas CO₂ removal efficiency was 85.46 ± 6.25%. Its removal efficiency of chemical oxygen demand, total nitrogen, and total phosphorus were 85.23 ± 8.32%, 87.10 ± 7.55%, and 92.40 ± 3.05%, respectively.

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Renewable Energy Global Innovations features: Superior Sodium Storage in Na2Ti3O7 Nanotube Arrays through Surface Engineering

Significance Statement

Sodium-ion batteries (SIBs) offer a promising scalable energy storage alternative to current lithium-ion batteries (LIBs). Titanium based SIB anode materials have attracted great interest owing to highly efficient Na storage activity, high stability, and low cost. The Na₂Ti₃O₇ structure is composed of zigzag layers of titanium oxygen octahedral, in which up to 3.5 Na ions per formula unit can be intercalated into the interlayer space and easily exchanged, leading to a capacity of 310 mAh g^–1.

This anode shows a low Na insertion potential (0.3 vs Na), leading to a higher operating voltage and energy density in practical batteries. However, the Na₂Ti₃O₇ still suffers from sluggish Na insertion/extraction kinetics resulting from a large bandgap of 3.7 eV and insufficient cycling stability for substantial Na insertion (>2 Na per unit formula) in the lattice due to the fact that the mechanical strain exists upon Na uptake and that the reactive surface sites cause unwanted electrolyte degradation and irreversible trapping of Na ions.

To attack these critical problems of reaction kinetics and surface trapping, for the first time, Prof. Liang Li’s group and their coworkers reported a novel surface engineering method by combining atomic layer deposition (ALD) and elemental doping (Adv. Energy Mater. 2016, 6, 1502568). The fabrication of the Na₂Ti₃O₇ electrode includes the hydrothermal growing of Na₂Ti₃O₇ nanotube arrays, surface ALD deposition of a thin TiO₂ layer, and subsequent sulfidation.

The nanoarrays exhibited high reversible capacities of 221 mAh g⁻¹ and a superior cycling efficiency and rate capability, retaining 78 mAh g⁻¹ at 10 C (1770 mA g⁻¹) over 10 000 continuous cycles. The full cells consisting of Na₂Ti₃O₇ nanotube anode and Na_2/3(Ni_1/3Mn_2/3)O₂ cathode deliver a specific energy of 110 Wh kg⁻¹.  

About The Author

Prof. Liang Li is a full professor in Soochow University, China. He received the Ph.D. degree from the Institute of Solid State Physics, Chinese Academy of Sciences and won the Excellent President Scholarship in 2006. From 2007-2012, he worked in National University of Singapore, Singapore, National Institute of Advanced Industrial Science and Technology, Japan, National Institute for Materials Science, Japan, and the University of Western Ontario, Canada.

Dr. Li’s research group focuses mainly on the energy conversion and storage devices of low-dimensional nanomaterials. He was awarded by China government as 1000 Youth Talents Plan and Excellent Youth Foundation in 2013 and 2014, respectively. His group web: http://ecs.suda.edu.cn  

Journal Reference

Advanced Energy Materials, 2016, Volume 6, Issue 11.

Jiangfeng Ni¹, Shidong Fu¹, Chao Wu², Yang Zhao¹, Joachim Maier², Yan Yu^2,3,4, Liang Li¹

Show Affiliations

1. College of Physics, Optoelectronics and Energy, Center for Energy Conversion Materials & Physics (CECMP), Soochow University, Suzhou, P. R. China
2. Max Planck Institute for Solid State Research, Stuttgart, Germany
3. Key Laboratory of Materials for Energy Conversion, Chinese Academy of Sciences, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei, P. R. China
4. State Key Laboratory of Fire Science (SKLFS), University of Science and Technology of China, Hefei, Anhui, P. R. China 

Abstract

Sodium-ion batteries have attracted extraordinary attention owing to their low cost and raw materials in abundance. A major challenge of practical implementation is the lack of accessible and affordable anodes that can reversibly store a substantial amount of Na ions in a fast and stable manner. It is reported that surface engineered sodium titanate (Na₂Ti₃O₇) nanotube arrays directly grown on Ti substrates can serve as efficient anodes to meet those stringent requirements. The fabrication of the nanotube arrays involves hydrothermal growing of Na₂Ti₃O₇ nanotubes, surface deposition of a thin layer of TiO₂, and subsequent sulfidation.

The resulting nanoarrays exhibit a high electrochemical Na-storage activity that outperforms other Na₂Ti₃O₇ based materials. They deliver high reversible capacities of 221 mAh g⁻¹ and exhibit a superior cycling efficiency and rate capability, retaining 78 mAh g⁻¹ at 10 C (1770 mA g⁻¹) over 10 000 continuous cycles. In addition, the full cell consisting of Na₂Ti₃O₇ nanotube anode and Na_2/3(Ni_1/3Mn_2/3)O₂ cathode is capable of delivering a specific energy of ≈110 Wh kg⁻¹ (based on the mass of both electrodes). The surface engineering can provide useful tools in the development of high performance anode materials with robust power and cyclability.

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Renewable Energy Global Innovations features: Computer simulations to maximise fuel efficiency and work performance of agricultural tractors in rotovating and ploughing operations

Significance Statement

Agricultural tractor is the one of the largest fuel consumers among agricultural machines. The tractor population is growing continuously and the tractor power also appears to increase in recent years. This trend is expected to continue and so is tractors’ fuel consumption in Korea. In addition, tractors should meet emission standards both in domestic and overseas markets. In response to such circumstances, tractor manufacturers are required to develop technologies to increase fuel efficiency of tractors and at the same time to reduce their emissions without any power loss.

In order to solve this problems, automatic control system for maximizing the fuel efficiency system will be necessary in the near future. There are many techniques for maximizing the fuel efficiency of agricultural tractor using engine, transmission and implements control separately. But few studies were conducted for investigate the interaction between separated control systems. For integrating the control system, effects of each control variables on fuel efficiency were analysed.

This study was conducted to investigate the effects of five control variables of a tractor: ballast, tyre inflation pressure, transmission gear, engine speed, and work load on fuel efficiency parameters. Tractor simulation model was developed and was validated using the field experiments results. Using the Using the tractor model, 162 simulations were performed under the various combinations of the control variables on the basis of a full factorial design. The simulation results were used to develop linear regression models from which strategies can be established to maximise fuel efficiency. The best strategy reduced FC, FCA, and SVFC by 81.3, 61.1, and 52% under ploughing, and by 58.9, 75.7 and 28.6% under rotovating operations, respectively, when compared with those for the worst strategy.

      

Figure Legend: Schematic of Tractor simulation model

About The Author

Jin Woong Lee is currently a senior researcher of LSMtron Co. tractor manufacturing company at Gyeonggi-do, Korea since 2014. He is interested in the design of control algorithm and control system architecture for agricultural tractor transmission and hydraulic system. He received a B.S and MS., and a Ph. D. degrees in Biosystems Engineering from Seoul National University, Korea.

About The Author

Jae Seung Kim studied automatic gear-shift algorithm for fuel efficiency of agricultural tractors in Off-road equipment design lab. He received a B.S. and MS degrees in Biosystems Engineering from Seoul National University, Korea. Now he works in Shinho systems Co., Ltd. since 2015 and is interested in the simulation of drivetrain and vehicle dynamics.

About The Author

Kyeong Uk Kim Has been a professor of Biosystems and Biomaterial Science and Engineering at Seoul National University specializing in farm power and machinery, soil-machine systems and life test of machine components. He has co-authored several books including principle of agricultural machines. He holds a BSc and MSc in Agricultural Engineering from Seoul National University and a PhD in Agricultural Engineering from University of Illinois at Urbana-Champaign USA (1981)

Reference

Biosystems Engineering, Volume 142, 2016, Pages 1–11.

Jin W. Lee, Jae S. Kim, Kyeong U. Kim

Department of Biosystems & Biomaterials Science and Engineering, Seoul National University, Seoul 151-921, South Korea.

This study was conducted to investigate the effects of five control variables of a tractor: ballast, tyre inflation pressure, transmission gear, engine speed, and work load on three fuel efficiency parameters: fuel consumption per work hour (FC), fuel consumption per tilled area (FCA) and specific volumetric fuel consumption (SVFC). This was done for moldboard ploughing and rotovating operations by computer simulation. A tractor model was constructed with four sub-models: engine and power train, fuel consumption, tractive performance, and draught and power requirement. The simulated fuel efficiency values were in a range of 3.3–6.5% error in average when compared with those obtained from field experiments carried out in a paddy field under the same operational conditions. Based on these results, the tractor model was considered acceptable for simulations to find a general relationship between the fuel efficiency parameters and the control variables.

Using the tractor model, 162 simulations were performed under the various combinations of the control variables on the basis of a full factorial design. The simulation results were used to develop linear regression models from which strategies can be established to maximise fuel efficiency. The best strategy reduced FC, FCA, and SVFC by 81.3, 61.1, and 52% under ploughing, and by 58.9, 75.7 and 28.6% under rotovating operations, respectively, when compared with those for the worst strategy.

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