Renewable Energy Global Innovations features: Graphene and Ag nanowires co-modified photoanodes for high- efficiency dye-sensitized solar cells

Significance Statement

Dye-sensitized solar cells (DSSCs) are an attractive solar energy conversion technology and have gained widespread attention in recent years because of their low cost of manufacture, ease of fabrication, tunable optical properties and long-term stability. In devices, photoanode plays an important role for the photoelectric performance. In order to obtain more efficient solar cells, most of researches have focused on increasing efficiency by improving the TiO₂ photoanodes by enhancing the absorption of light, suppressing the recombination of charges and improving the energetics on interfaces.

In this work, a multistage structure DSSC, consisting of Ag nanowires (AgNWs), TiO₂ nanoparticles and graphene wrapped TiO₂ mesoporous microspheres, was reported. The mesoporous TiO₂ microspheres used as a light scatting layer had not only large surface area but also porous structure so that dye loading was enhanced and light utilization efficiency was improved. The power conversion efficiency (PCE) of the DSSC without microspheres as light scatting layer was just 3.53% whilst that for DSSC with mesoprous microspheres was 4.95%. Furthermore, graphene as a special two-dimensional honeycomb crystal structure carbon nanomaterial had a large theoretical specific surface area, high carrier mobility, unique electronic properties and high transparency. Additionally, the UV–vis absorption result showed a red-shift in the absorption edge and a strong absorption in the visible light range for it. The light absorption range of graphene modified TiO₂ microspheres was also significantly wider than the sample without graphene, indicating better light absorption ability for graphene-wrapped microspheres. Owing to these properties, herein, graphene was used to couple with TiO₂ microspheres to form a good composite material used for the further promoted photoanode of a DSSC. This has been proved from the result of the optical diffuse reflectance spectra (DRS), the bandgap of anatase TiO₂ microsphere was reduced from 3.26 eV to 2.86 eV by modifying graphene. The more narrow bandgap directly led to the lower level of energy used for activating the electrons from the valence band to the conduction band. As a result, the light absorption of photoanode film was significantly enhanced in the visible light region and in turn the conversion efficiency for DSSCs gained great promotion. Moreover, Ag nanowires could not only reduce the surface trap states of TiO₂ but also enhance the surface plasmonic resonance and rapid interfacial charge transfer between Ag nanowires and TiO₂, thereby suppressing charge recombination, promoting charge transfer and improving DSSC efficiency. Additionally, the 1D Ag nanowires had superior electrical conductivity and the interconnected uniform 2D electrical conductive network of Ag nanowires could provide a fast and effective electron transport pathway. All these contributions from the modification of photoanodes led to an achievement of a PCE of 7.42% for the DSSC co-modified by graphene and Ag nanowires, which was about TWICE as much as that for the DSSCs only with a TiO₂ nanoparticle layer (with a PCE of 3.53%).

This work not only sheds some lights on the effect of the modification of metallic oxide structure and ions in the channels on the development of high performance photoanode but also might provide a new reference method for the improvement of the power conversion efficiency for the DSSCs.

About The Author

Haoran Yan is a Ph.D. student at the School of Materials Science and Engineering, Southwest Jiaotong University, China. His research interest is focusing on the preparation of nano-sized titanium dioxide compound materials and their application in dye-sensitized and perovskite solar cells. His current research is focusing efficient perovskite hybrid solar cells via interfacial modification engineering.

Journal Reference

Solar Energy,Volume 122, December 2015, Pages 966–975.

Haoran Yan, Jianxin Wang^, , Bo Feng, Ke Duan, Jie Weng

Key Laboratory of Advanced Technologies of Material, Minister of Education, School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610031, Sichuan, PR China

Abstract

In the present work, a novel multistage structure dye-sensitized solar cell (DSSC), which consists of Ag nanowires (AgNWs), TiO₂ nanoparticles and graphene wrapped TiO₂ mesoporous microspheres (GTMs), was fabricated by using simple spin coating steps. The aim of this study was to modify the bandgap of GTMs by using graphene so as to promote the light absorption of GTMs in the visible light region and in turn to improve the power conversion efficiency (PCE) of DSSCs. Additionally, graphene and Ag nanowires can enhance the electron transfer in the DSSC to further improve the PCE of DSSCs. The effect of AgNWs and GTMs light scatting layer on the photovoltaic performance of DSSCs was investigated. The results showed that a PCE of 7.42% was achieved for the DSSC co-modified by GTMs and Ag nanowires, which was about twice as much as that for the DSSCs only with a TiO₂ nanoparticle layer (with a PCE of 3.53%). This present study might open a new avenue for the improvement of the PCE of DSSCs.

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Renewable Energy Global Innovations features: Promotion of microalgal growth by co-culturing with Cellvibrio pealriver using xylan as feedstock

Significance Statement

Microalgal biodiesel is a promising biofuel with potential for sustainable fuel production. To promote biomass and lipid production, a series of strategies are being developed, such as: mixotrophic and heterotrophic growths of microalgae on organic carbon sources or industrial wastes, or cultivation coupled with wastewater treatment plants.

Xylose is the major components among hemicellulose and rich in corn and rice straws, sugarcane bagasse, and grass. However, xylose is unable to directly use by wild type yeast or algae due to the xylose toxicity or deficient xylose transmembrane transport. Microalgal cultivations with xylose as carbon source have been reported in some xylose tolerant strains via mixotrophic or heterotrophic growths, or previous activation of glucose transporters.

In this paper, we constructed a bacterial-microalgal consortium for enhancing microalgal growth and lipid production. In the consortium, a xylanolytic bacterium Cellvibrio pealriver PR1 hydrolyzes xylan to xylose, which is then metabolized to some active substances through xylose isomerase or xylulokinase; the active substances are used for the growth and lipid production by microalgae. Based on the consortium, the mixotrophic growths of Chlorella sacchrarophila, Chlorella pyrenoidosa, Dunaliella sp. and Chlamydomonas reinhardtii were 2 to 3.3 folds higher than photoautotrophic growths, and equal to the mixotrophic growths with glucose as carbon source; the lipid production were 1 to 1.3 folds higher than the mixotrophic growths with glucose, and 1 to 1.5 folds higher than the photoautotrophic growths.

It was noted that the bacterial-microalgal consortium is a potential method to produce low-cost microalgal biodiesel by using cheap agricultural or industrial wastes.  

About The Author

Zhangzhang xie is currently a Ph.D. candidate in the major of Microbiology in School of Bioscience and Bioengineering at South China University of Technology. He focuses on the research of promoting the biomass and lipid production from microalgae.

About The Author

Weitie Lin is a professor in School of Bioscience and Bioengineering at South China University of Technology. He received his Ph.D. degree in fermentation engineering from South China University of Technology in 1991. He is the first Ph.D. candidate in the major of fermentation engineering in China. His present research interests include: 1) fermentation engineering in microbiology and food science; 2) application of microbiology for agricultural waste treatment and recycle; 3) microbial ecology in natural environment, agricultural and industrial wastewater treatment systems.  

About The Author

Jianfei Luo is an associate professor in School of Bioscience and Bioengineering at South China University of Technology. He received his Ph.D. degree in fermentation engineering from South China University of Technology in 2011. His present research interests focus on the microbial interaction with microorganism and environment during food fermentation, environmental bioremediation, and bioenergy development.  

Journal Reference

Bioresour Technol 2016 Jan 23;200:1050-4. Epub 2015 Oct 23.

Zhangzhang Xie, Weitie Lin, Jianfei Luo

Guangdong Key Laboratory of Fermentation and Enzyme Engineering, School of Bioscience and Bioengineering, South China University of Technology, Guangzhou 510006, PR China.

Abstract

In this work, a Cellvibrio pealriver-microalga co-cultivation mode was used to promote the growths of four microalgae by using xylan as feedstock. After 12days of cultivation, the biomass concentrations of Chlorella sacchrarophila, Chlorella pyrenoidosa and Chlamydomonas reinhardtii in co-cultivation were equal to those in mixotrophic growth on glucose, and the Dunaliella was about 1.6-fold higher than that on glucose.

The comparative transcriptomes analysis demonstrated that the xylose and xylan hydrolysates were catalyzed to some active substrates by C. pealriver via some functional enzymes; these active substrates are possibly responsible for the promotion of microalgal growth. This C. pealriver-microalga co-cultivation mode is a potential method to produce low-cost microalgal biodiesel by using hemicellulose as feedstock.

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Renewable Energy Global Innovations features: Effect of pre-thermal treatment on the lithium storage performance of LiNi0.8Co0.15Al0.05O2

Journal Reference

Journal of Materials Science,  2016, Volume 51, Issue 3, pp 1400-1408.

Zewen Ruan, Yongming Zhu , Xiangguo Teng

Department of Applied Chemistry, Harbin Institute of Technology at Weihai, Wenhua West Road 2#, Weihai, 264209, Shandong Province, China.

Abstract

Layered LiNi_0.8Co_0.15Al_0.05O₂ cathode materials have been synthesized by co-precipitation methods. The effect of pre-thermal treatment was investigated by thermogravimetric differential thermal analysis. Although X-ray diffraction has confirmed that all diffraction peaks in XRD patterns for samples treated at 500 ~ 750 °C can be a well-indexed hexagonal structure, the status of nickel ions varied. Samples pre-treated at different temperatures show different colors and had various contents of Ni³⁺ measured by XPS. Powders that heated again at 800 °C under the condition of dried oxygen for 12 h after pre-thermal treatment show different electrochemical performances, which pre-thermal treated at 600 °C had a highest reversible specific capacity about 180 mAh·g⁻¹and capacity retention of 91.7 % after 50 cycles when cycled at a current density of 0.1 C between 2.5–4.3 V at room temperature. The relationship between the status of nickel ions and electrochemical performance was discussed. On the other hand, the capacity retention rates are 91.7, 96.6, and 98.0 % after 50 cycles at 0.1 C and at 100 %DOD, 80 DOD, and 50 %DOD.

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Renewable Energy Global Innovations features: Highly Efficient Photoelectrocatalytic Reduction of Hexavalent Chromium based on the Cascade Energy Transfer towards Using no Semiconducting Photocatalysts

Significance Statement

The modern society especially the developing and undeveloped countries is suffering from the increasingly severe environmental pollution mostly caused by hazardous matters, such as toxic heavy metal ion Cr(VI). The most desirable way to remove Cr(VI) is suggested lie on the use of solar irradiation which is cheap and endless. The photocatalytic removal of Cr(VI) based on semiconductor oxide photocatalyst has been provided, however, due to the low efficiency, high cost, and difficulty of recycling photocatalyst powder from the aqueous solution, this method cannot be popularized at the economical level. Hence, it is of urgent priority to design novel methods to utilize the solar light and then lead to the efficient removal of toxic metal ions. Here, we construct an energy relay structure based on citric acid, Ti anode, and Cr(VI), whereby the Cr(VI) are efficiently reduced to Cr(III) under the UV irradiation. As shown in the image, upon the photoexcitation of the citric acid, the electron transfer from citric acid to Ti anode occurs efficiently, mostly because the positively biased Ti is able to facilitate the separation of electrons from holes left in citric acid. Then, the photogenerated electrons in Ti anode spontaneously flow to Cr(VI), which is a energetically favorable process, leading to the efficient reduction of Cr(VI) under the condition that no semiconductor oxide photocatalyst is present in the whole reaction. The method we provide is simple, easy-to-set up, and highly efficient, offering a big step towards the purification of waste water at the commercial level.

About The Author

Jing Shang is an associate professor at the department of environmental science and engineering at Peking University since the year of 2004. She received her Ph.D in environmental science from Jilin University, Changchun city in China, in 2001. From 2001 to 2003, she conducted postdoc research in the department of chemistry at Tsinghua University. She develops novel photoelectrochemical technologies to efficiently remove organic and inorganic pollutants, and is now working on the atmospheric chemistry as well.

Journal Reference

Electrochimica Acta, Volume 188, 2016, Pages 752–756.

Xiang Feng, Jing Shang, Tong Zhu

State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, PR China

Abstract

Highly efficient photoelectrocatalytic (PEC) reduction of Cr(VI) has been realized in the absence of semiconducting photocatalysts. In the novel-configuration cell using Ti anode, Pt cathode, Cr(VI), and citric acid, the rate constant of the photoelectrocatalytic reduction of Cr(VI) at a bias of 1.5 V was almost 3 times than that in the conventional-configuration cell using ITO/TiO₂ anode, Ti cathode, Cr(VI), and citric acid. It was mostly because the citric acid, Ti anode, and Cr(VI) formed an energy-relay cascade structure, in which the photogenerated electrons in the citric acid were transferred to the positively biased Ti and then from anode to Cr(VI), leading to the very efficient Cr(VI) reduction. We develop a simple photoelectrocatalytic method to reduce Cr(VI) over the Ti anode sensitized by photoexcited organic dye in no need of metal oxide photocatalysts, which can be considered as an important advance towards the cost-effective, environmentally friendly treatment of waste water.

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Renewable Energy Global Innovations features: Hydrogen storage properties and mechanisms of magnesium based alloys with mesoporous surface

Significance Statement

The United Nations Conference on Climate Change held in Paris charts the course for green, circular and low-carbon development featuring both economic growth and an effective response to climate change. One of the effective and sustainable methods is increasing the share of the renewable energy in the energy consumption structure.

Nowadays, hydrogen energy has been viewed as a kind of ideal renewable energy due to its non-pollution, abundant source and cyclic utilization. In order to achieve the practical applications of hydrogen energy, an efficient, safe and economic hydrogen storage technology is a key issue.

Mg-based metal hydride is one of the most promising candidates for hydrogen storage because of its low cost, high hydrogen storage capacity, good safety and environmental benignity. Unfortunately, high reaction temperature during hydrogen absorption/desorption processes imposes restrictions on the applications of Mg-based metal hydride. Lowering the reaction temperature has become crucial for Mg-based metal hydride hydrogen storage material.

Our research is aimed to reduce the hydrogen absorption/desorption temperature, thus improving the low-temperature hydrogen storage properties of Mg-based metal hydride, which is the hot topic in the field of hydrogen storage technology. A new kind of mesoporous material with the highly developed surface, called as HDS Mg-Ni hydride, is designed based on conventional Mg-based hydride. The new method of mechanically alloying and subsequent alkali washing was applied to prepare the HDS Mg-Ni hydride.

On the basis of our observations, the specific surface areas of this kind of Mg-based mesoporous material are 5~10 times as large as those of conventional Mg-based hydride. The larger specific surface area with abundant mesopores provides more and easier paths for the diffusion of hydrogen into the unreacted layer, thus facilitating the hydrogen absorption/desorption processes of Mg-based hydride. As a result, the HDS Mg-Ni hydride has favorable hydrogen storage properties at low temperatures. The hydrogen absorption/desorption temperature is remarkably reduced to near room temperature. According to a study on the hydrogen storage mechanisms, it was also found that the hydrogen storage capacity could be further increased by mixing other hydrogen storage materials into the HDS Mg-Ni; for example, activated carbon. The synergistic effects between the HDS Mg-Ni and activated carbon could lead to an increase of about 30% in the hydrogen storage capacity of the composite system. The improvements in the reaction temperature and hydrogen storage capacity make Mg-based metal hydride more attracting in the practical applications of hydrogen storage technology. Besides, it is significant and helpful in the design and development of new advanced Mg-based composite systems for hydrogen storage.

About The Author

Zhen Wu, Assistant professor, School of Chemical Engineering and Technology, Xi’an Jiaotong University. He received his Ph.D. degree in Power Engineering and Engineering Thermophysics from Xi’an Jiaotong University. From Sep 2013 to Sep 2014, he obtained the National Government Study Abroad Scholarship to make research in Kyoto University as a visiting scholar. Now he is undertaking the National Natural Science Foundation of China (No. 51506174), the General and Special Programs of China Postdoctoral Science Foundation (No. 2015M570830) and Fundamental Research Funds for the Central Universities (No. xjj2016047) as the project leader. In 2015, his paper published in Applied Energy was awarded as the ‘Best Paper Award of Excellence‘ jointly by Elsevier Publishing Co. Ltd. and the prestigious international journal of Applied Energy. His research interests include: 1) Design and development of advanced hydrogen storage materials. 2) Optimal design of hydrogen storage reactors. 3) System integration of on-board hydrogen source unit and energy management of integrated on-board hydrogen source system.

About The Author

Zaoxiao Zhang, Professor, Dean of Department of Chemical Process Equipment, Xi’an Jiaotong University. He received his Ph.D. degree in Power Engineering and Engineering Thermophysics from Xi’an Jiaotong University in 1998. During the period of 2001 – 2004, he successively worked in Japanese International Cooperation Agency (JICA) and the University of Queensland, Australia, as a visiting scholar. So far, he has undertaken more than 30 projects from the National Natural Science Foundation of China, Chinese Ministry of Education and the industries. His research work has been awarded by Chinese Ministry of Education, Beijing City Government and China Petrochemical Corporation (Sinopec Group), respectively. He has been involved with the research of energy system optimization. Since he has lots of cooperation experiences with the industries, he combines industrial demand and lab studies to build an interdisciplinary research program with emphasis on energy system and fossil fuel resources. An important research field in the last ten years is the energy and environmental technologies for the increase of the energy efficiency and reducing CO₂ emissions in the industrial processes. He has published more than 100 peer-reviewed papers, 10 patents, 5 academic monographs and delivered more than 50 presentations in academia and industry up till now.

About The Author

Fusheng Yang is an associate professor in the School of Chemical Engineering and Technology at Xi’an Jiaotong University, Xi’an, China. He got his Ph.D. degree at the same university in 2010 and once worked as postdoctoral researcher at Tokyo University of Science, Noda, Japan. His present research interests include: 1) Development of novel metal hydride reactor prototype for heat & mass transfer enhancement. 2) Consistent measurement and modeling of P-C-T properties and intrinsic hydriding/dehydriding kinetics of metal hydride materials. 3) Industrial applications of energy saving techniques, such as steam ejector based heat pump. He has published about 20 peer-reviewed journal papers, 1 book chapter, and delivered ~10 presentations in academia and industry.

About The Author

Penghui Feng is currently a Ph.D. candidate in the major of Power Engineering and Engineering Thermophysics in School of Chemical Engineering and Technology at Xi’an Jiaotong University. He focuses on the research of high temperature thermal storage technology based on metal hydrides. 

About The Author

Yuqi Wang received his Ph.D. degree from Xi’an Jiaotong University specializing in power engineering and engineering thermophysics. Now he is currently a professor in School of Chemical Engineering at Northwest University. From Mar 2009-Sep 2009, he worked in Low Carbon Green Technology Laboratory, University of Nevada(Reno) as a visiting scholar. Dr. Wang proposed several new type of metal hydride reactors and conducted a few simulation study on metal hydride heat pumps and thermal compressors. Now he is undertaking 6 projects including Natural Science Foundation of China and other projects from Ministry of Science and Technology, Shaanxi government. He has published more than 60 academic papers, authorized 10 national invention patents, and he was awarded 22 teaching and scientific research prizes, like “the China Young Backbone Teacher Scholarship” and “the second prize of Science and Technology at Shaanxi Institutions of Higher Learning (15C21)”. He was awarded in 2008. His research focuses on: 1) H₂ storage kinetics and investigation of metal hydride reactor. 2) Chemical energy engineering and hydrogen Energy. 3) Supercritical fluid technology. 4) Reforming and transfer reaction of CH₄ and utilization of clean energy.

Journal Reference

International Journal of Hydrogen Energy, Volume 41, Issue 4,  2016, Pages 2771-2780.

Z. Wu¹, Z.X. Zhang^1,2, F.S. Yang¹, P.H. Feng¹, Y.Q. Wang³ 

Show Affiliations

1. School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China
2. State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China
3. School of Chemical Engineering, Northwest University, Xi’an 710069, People’s Republic of China

Abstract

A new kind of magnesium based hydrogen storage alloy with highly developed surface (HDS) was prepared using the technique of mechanical alloying followed by alkali washing in this paper. The phase composition, morphology, hydrogen storage properties and mechanisms of the alloy thus prepared, named HDS Mg-Ni, were further investigated by multiple methods including X-ray diffraction, scanning electron microscope, Sieverts volumetric method and differential scanning calorimeter. The specific surface area, average pore size and pore volume of the alloy are 50.95 m² g⁻¹, 36.2 nm and 0.34 cc g⁻¹, respectively. Also, it was discovered that the HDS Mg-Ni powder takes in about 0.65 wt.% of hydrogen even at a low temperature of 323 K, at which the conventional Mg and Mg₂Ni materials could not react with H₂. It suggests that the highly developed surface remarkably improves the hydrogen storage properties at low temperatures. Besides, the synergistic effects between the HDS Mg-Ni powder and activated carbon(AC) on the improvement of low-temperature behaviors were discussed. The results showed that the addition of AC further improves the hydrogen capacity and absorption kinetics due to the increased specific surface area, providing easier and more paths for the diffusion of hydrogen into the alloy powder.

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Renewable Energy Global Innovations features: Electrochemically-controlled grafting of hydrophilic brushes from conducting polymer substrates

Significance Statement

Graft copolymers with a conducting polymer backbone are a promising class of material for the design of functional surfaces. Such materials are particularly well-suited to organic electronics applications such as polymer solar cells. This class of graft copolymer takes advantage of the electroactivity and optical properties of the conducting polymer backbone, with grafted sidechains selected to impart desired chemical, mechanical, and/or physical properties.[1–6]

Electrochemically-mediated ATRP (eATRP) has emerged in recent years as an alternative controlled radical polymerisation technique that utilises low concentrations of copper-based ATRP catalysts, and that can be conducted in the presence of atmospheric oxygen.[17–20]   We have adapted this versatile new technique to perform surface-initiated electrografting directly from a conducting polymer-functionalised substrate that acts as both a macroinitiator for polymer brush grafting, and as the working electrode to control catalyst oxidation state, and thereby catalyst activity. This new method of surface-initiated grafting from conducting polymer, once optimised, could provide a versatile tool for the synthesis of thin film polymer electronics with a high level of control over architecture and chemistry.

References:

[1] C.-H. Lin, W.-J. Chou, J.-T. Lee, Macromol. Rapid Commun. 2012, 33, 107–113.[2] M. F. Abasıyanık, M. Şenel, J. Electroanal. Chem. 2010, 639, 21–26.[3] Y. Yagci, L. Toppare, Polym. Int. 2003, 52, 1573–1578.[4] C. D. Grande, M. C. Tria, G. Jiang, R. Ponnapati, Y. Park, F. Zuluaga, R. Advincula, React. Funct. Polym. 2011, 71, 938–942.[5] L. T. Strover, J. Malmström, O. Laita, J. Reynisson, N. Aydemir, M. K. Nieuwoudt, D. E. Williams, P. R. Dunbar, M. A. Brimble, J. Travas-Sejdic, Polymer. 2013, 54, 1305–1317.[6] Y. Pei, J. Travas-Sejdic, D. E. Williams, Langmuir 2012, 28, 8072–8083.[7] N. Bortolamei, A.A. Isse, A.J.D. Magenau, A. Gennaro, K. Matyjaszewski, Angew. Chemie. 2011, 123, 11593–11596.[8] A. Magenau, N. Strandwitz, A. Gennaro, K. Matyjaszewski, Science 2011, 332, 81–84.[9] S. Park, H. Cho, K. Wegner, Macromolecules 2013, 46, 5856–5860.[10] A.J.D. Magenau, N. Bortolamei, E. Frick, S. Park, A. Gennaro, K. Matyjaszewski, Macromolecules, 2013, 46, 4346–4353. 

About The Author

Lisa T. Strover joined the Alexandre Yersin Department of Solar Energy and Environmental Physics (YDSEEP) at the Ben-Gurion University of the Negev, Israel, in June 2016. She completed her BSc(Hons) (2010) and Ph.D. (2016) in Chemistry within the Polymer Electronics Research Centre at the University of Auckland, with her research focusing on electroactive graft copolymer brushes for functional surfaces and electrochemically mediated ATRP from conducting polymer substrates.

About The Author

Jenny Malmström joined the Department of Chemical and Materials Engineering at the University of Auckland as a Lecturer in 2016. She received her MSc degree in Bioengineering at Chalmers University of Technology, Gothenburg, Sweden (2004) and a Ph.D. in Nanoscience at the University of Aarhus, Denmark (2010). From Denmark she moved to Auckland, where she joined the School of Chemical Sciences (UoA) as a post doctoral research fellow. Her research focuses on creating functional biointerfaces to understand and control biological systems.

About The Author

Jadranka Travas-Sejdic is a Professor at the School of Chemical Sciences, Director of the Polymer Electronics Research Centre at the University of Auckland, and a principal investigator at the MacDiarmid Institute for Advanced Materials and Nanotechnology. Her research interests are in the fields of advanced polymeric materials for biosensing and bioelectronics, electrically and environmentally responsive polymers and surfaces, actuators, materials for tissue engineering and nanostructured conducting polymers. She has (co)authored over 200 publications, including eight book chapters. 

Journal Reference

Electrochimica Acta, Volume 188,  2016, Pages 57–70.

Lisa T. Strover^1,2, Jenny Malmström^1,2, Louise A. Stubbing¹, Margaret A. Brimble^1,2, Jadranka Travas-Sejdic^1,2 

Show Affiliations

1. Polymer Electronics Research Centre, School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
2. MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington, New Zealand  

Abstract

Electrochemically-mediated ATRP (eATRP) has emerged in recent years as an alternative controlled radical polymerisation technique that utilises low concentrations of copper-based ATRP catalysts, and that can be conducted in the presence of atmospheric oxygen. In this work, we adapt eATRP to perform surface-initiated electrografting directly from a conducting polymer (CP) macroinitiator that also acts as the working electrode to control catalyst oxidation state, and thereby catalyst activity. Aqueous electrografting of hydrophilic poly(2-hydroxyethyl methacrylate) polymer brushes from the conducting polymer macroinitiator, in the presence of an ATRP catalyst (CuBr₂/TPMA), was confirmed by ATR-FTIR, water contact angle measurements, and XPS. Optimised grafting conditions were determined whereby polymerisation kinetics approached first order characteristics, as expected for grafting via an eATRP mechanism. However, even under these optimised conditions, we determined that competing electrografting mechanisms were likely occurring, with experiments supporting the occurrence of polymerisation in solution, followed by ‘grafting to’ reactions, as previously described for electrografting via surface electro-initiated emulsion polymerisation (SEEP). Additionally, spectroelectrochemical studies suggest that the mechanism of initiation differs from previously reported eATRP systems in that the conducting polymer itself acts as a co-reductant for the catalyst. As expected, the prevalence of uncontrolled grafting, due to competing grafting mechanisms, as well as effects such as chain termination and degrafting, was highly dependent on polymerisation conditions, most notably on the applied potential.

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Renewable Energy Global Innovations features: Enhancement of heat dissipation of LED module with cupric-oxide composite coating on aluminum-alloy heat sink

Significance Statement

Heat dissipation using thermal radiation is a novelty and clean method to energy conversion technology in electronics and mechanics. Most of the heat dissipation methods have been developed based on the principle of conduction and convection, whereas radiative heat transfer has not been considered because the emissivity of metallic aluminum surface is relatively low, approximately 0.1 ~ 0.2.  In the context of LEDs, various approaches, such as solder, thermal interface materials and metal-core printed circuit boards (MCPCBs), have been used to solve the heat dissipation problems.

 Our research group have been studied about more effective method for heat dissipation of LEDs, then the surface of aluminum alloy substrate was modified to increase the emissivity. The cupric oxide (CuO) has the higher emissivity in the whole materials around 0.96, a various distribution of particle size was implemented to evaluate the heat dissipation performance. Thermal resistance, emissivity, and continuous operation were carried out to investigate the possibility that a suitable coating layer of low thermal resistance can enhance the radiative heat dissipation and hence the overall heat dissipation performance.

 Lower LED operating temperatures and thermal resistances indicate superior heat dissipation performance. The significantly improved heat dissipation performance of the LED system was achieved by applying a composite coating with high radiative emissivity on an aluminum-alloy heat sink. The composite coating was composed of CuO nano-powders and silicon-based resin, having the thermal emissivity of ∼0.9 which is nine times greater than that of bare aluminum. The densely-coated composite layer with the enhanced the thermal emissivity of the surface improved the radiative heat dissipation significantly, enabling to reduce the thermal resistance of the heat sink and hence the total thermal resistance of the LED module up to ∼15%. Coating thickness affected the heat dissipation performance of the heat sink. In this study, the coating thickness of ∼200 μm showed the best performance. The composite coating, having the emissivity close to a black body, not only reduced the operating temperature of the LED chip but also allowed the stable heat dissipation with no significant degradation of the performance even under the elongated operation time. In conclusion, the use of a CuO-composite coating on a heat sink provides an effective means of enhancing radiative heat dissipation and increasing the LED life-time. 

About The Author

Donghyun Kim received his bachelor (2011), master, and doctoral (2016) degree in Department of Materials Science and Engineering (Nano-electrochemistry Lab) at Pusan National University, South Korea. His research field is “Electrochemistry”, “Wet Surface Treatment”, and “Heat dissipation via Thermal Radiation”. He published lots of paper about electrochemical surface and thermal radiation performance in SCI(E) journal.

About The Author

Wonsub Chung is currently a Professor in Department of Materials Science and Engineering at Pusan National University. He received his Ph. D. (1989) at Kyushu University, major is a chemical metallurgy. He teaches now “Corrosion and Anti-corrosion”, “Chemical Metallurgy”, and “Making Steel and Iron” and is a leader in Nano-electrochemistry Lab. In addition, his research is focused on thermal radiation performance, eco-friendly environmentally process, and wet surface treatment.  

Journal Reference

Energy Conversion and Management, Volume 106, December 2015, Pages 958–963.

Donghyun Kim¹, Junghoon Lee², Junho Kim³, Chang-Hwan Choi², Wonsub Chung¹

Show Affiliations

1. Department of Materials Science and Engineering, Pusan National University, Busan 46241, South Korea
2. Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA
3. Korea Institute of Industrial Technology (KITECH), Busan 46742, South Korea

Abstract

A composite coating composed of cupric oxide (CuO) and silicon-based resin was applied to an aluminum-alloy heat sink for a light emitting diode (LED) module. The purpose of the composite coating is to improve the heat dissipation performance of heat sink by enhancing thermal radiation emission. The heat dissipation performance was investigated in terms of LED junction temperature and thermal resistance using a thermal transient method. The CuO and silicon-based resin composite coating showed higher emissivity, and the lower junction temperature and thermal resistance of the heat sink was achieved. In addition, a continuous operation test of the LED chip with the heat sink revealed that the surface treated with the CuO composite coating stably dissipated heat without degradation. In conclusion, the composite coating proposed here showed a significant improvement of the heat dissipation performance of the aluminum-alloy heat sink due to the enhanced thermal radiation property.

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