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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