Flexible thermoelectric nanogenerator based on MoS2/graphene nanocomposite and its application for a self-powered temperature sensor

Significance Statement

New energy technologies have emerged that aim at harvesting environmental energy, which more often than not goes to waste, in a fashion that is clean and sustainable. The nanogenerator based on the pyroelectric effect, and more recently the thermoelectric effect, has been demonstrated to be an efficient and effective approach to harvesting environmental energy though both strategies exhibit shortcomings such as either low energy output or low efficiency. Thermoelectric nanocomposites have been developed by combining several nanomaterials to overcome the low efficiency, with special attention to the two-dimensional nanomaterial molybdenum disulfide, and graphene, which integrate the advantages of the two materials and avoids their weaknesses.

In a recent research published in Semiconductor Science and Technology, Yannan Xie and Zong-Hong Lin developed a flexible thermoelectric nanogenerator that is based on the molybdenum disulfide-graphene nanocomposite, which exhibits enhanced energy output and which can be applied as a temperature measurement sensor that is self-powered.

The authors prepared the molybdenum disulfide nanomaterials using a hydrothermal process, and mixed this with graphene paste in order to form the nanocomposite. The mixture was applied onto an indium tin oxide-polyethylene terephthalate substrate and dried to form the thermoelectric layer. The indium tin oxide layer and a silver paste were employed as the bottom and top conductive electrodes respectively, and the as-prepared nanocomposite as the thermoelectric layer in-between.

The research team observed that the molybdenum disulfide nanomaterial exhibits a nanoflower-like morphology of 1µm average size, and is made up of nanosheets that are well-dispersed. The nanosheets are composed of layered morphologies with 0.62 nm lattice spacing. Further, the nanomaterials exhibited 2 characteristic Raman bands at 360 cm-1 and 406-1. The thicknesses of the substrate and the molybdenum disulfide-graphene nanocomposite layers were noted to be 780 µm and 580 µm respectively.

From the analysis of the current-voltage characteristics between the as-developed device and pristine graphene and pristine molybdenum disulfide, it was noted that an ohmic contact was formed between the thermoelectric materials and the electrodes. Also, the as-developed nanocomposite displayed improved electrical conductivity as compared with pristine molybdenum disulfide, largely attributed to the presence of graphene which facilitates additional electron transport channels.

Further tests showed that with an increasing trend of temperature difference in the as-prepared device, there was a corresponding increase in voltage output, and the reverse was also true. At -35K, the as-developed device generates a -0.73mV output voltage, which is about 2 and 8 times larger as compared with devices having pristine molybdenum disulfide and pristine graphene respectively. The as-developed device has a power density of about 8.8nW/cm2, and a Seebeck coefficient of about 21µV/K as compared with 11µV/K for pristine molybdenum disulfide.

The polyethylene terephthalate substrate imparted the device with shape-adaptive and ultra-flexible properties, which grants it a wide range of applications for thermoelectric nanogenerators such as self-powered sensing. The authors tested this with a glass bottle having the thermoelectric nanogenerator to detect solution temperature, and noted the variation tendency between the output voltage and temperature differences fit a good linear relationship, which indicates its likely application in temperature sensors that are self-powered.

Flexible thermoelectric nanogenerator based on MoS2 graphene nanocomposite and application for a self-powered temperature sensor.- Advances in Engineering

About The Author

Dr. Yannan Xie is currently the Deputy Director and Assistant Professor of the Institute for Energy Efficiency Engineering in the College of Energy at Xiamen University. He received his B.S. in Applied Physics from Nanjing University of Science and Technology and Ph.D. in Microelectronics from Xiamen University. His research interests focus on nanogenerators, self-powered systems, and energy harvesting technology.

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About The Author

Ting-Mao Chou received his B.S. degree in 2015 from Department of Biomedical Engineering, Chung Yuan Christian University. He is currently a graduate student in Institute of Biomedical Engineering, National Tsing Hua University. His research focuses on the development of flexible electronics and preparation of nanomaterials for biomedical applications.

About The Author

Dr. Weifeng Yang is currently a Research Scientist of the Institute of Materials Research and Engineering in the Agency for Science, Technology and Research of Singapore. He received his B.S. and Ph.D. in Physics from Xiamen University. His research interests focus on optoelectronic materials & devices, semiconductor physics & technology, and optical spectroscopy.

About The Author

Minghui He received her Bachelor of Engineering degree in 2016 from Department of Thermal Power and Energy Engineering, Guizhou University. She is currently a graduate student in Institute of Energy Efficiency Engineering, Xiamen University. Her research interests include the development of self-powered system, flexible electronics and preparation of nanomaterials for optoelectronic devices and energy harvesting application.

About The Author

Dr. Yingru Zhao is currently the Director and Associate Professor of the Institute for Energy Efficiency Engineering in the College of Energy at Xiamen University. She received his B.S. and Ph.D. in Physics from Xiamen University. Her research interests focus on comprehensive experience in multi-scale modelling and optimization of complex energy systems.

About The Author

Dr. Ning Li is currently the Dean and Professor of the College of Energy at Xiamen University. He received his B.S. in Physics from the University of Science and Technology of China and Ph.D. from the University of California Santa Barbara. His research interests focus on new energy technologies and energy efficiency engineering.

About The Author

Zong-Hong Lin is an Associate Professor in Institute of Biomedical Engineering, National Tsing Hua University. Prof. Lin received his Ph.D. degree from Department of Chemistry, National Taiwan University.

His research interests include the development of high-output nanogenerators with smart designs, self-powered systems as biomedical and environmental sensors, highly efficient and stable catalysts for electrochemical applications, and functional nanomaterials for controlled antibacterial activity.

Reference

Yannan Xie, Ting-Mao Chou, Weifeng Yang, Minghui He, Yingru Zhao, Ning Li, Zong-Hong Lin. Flexible thermoelectric nanogenerator based on the MoS2/graphene nanocomposite and its application for a self-powered temperature sensor. Semiconductor Science and Technology, 32 (2017) 044003.

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