Tailoring
A A the surface chemistry of ZnO-Carbon A A wearable thermoelectric applications
cloth for Renewable Energy
A Pandiyarasan Veluswamy, and Hiroya Ikeda A A
Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan. Graduate School of Science and Technology, Shizuoka University, Hamamatsu, Japan. Email: pandiyarasan@yahoo.co.in
Abstract
In this work, carbon fabric with uniform ZnO layers on the surface was successfully synthesized via a simple solvothermal method. The morphology, structural, chemical composition,
optical, electrical and thermopower properties of ZnO-coated carbon fabrics was investigated. It was found that the volume of the zinc nitrate, hexamine and reaction time played important roles for the formation of uniform ZnO coatings on carbon fabric. The ultraviolet ray protection factor (UPF) of the fabric coated with ZnO could reach up to 201.7 but bare carbon fabric will be 28.62, meaning that high concentration hexamine could dramatically enhance the UV-shielding property. Furthermore, the ZnO coated carbon fabric also reported excellent electrical conductivity. The thermopower value of the ZnO coated carbon fabric could reach -0.054 µVK-1. It was expected that such conductive fabric has extensive application in wearable thermoelectric devices.
Introduction
Activity
Kilocal/hr Watts
Sleeping
70
81
Lying quietly
80
93
Sitting
100
116
Standing
110
128
Conversation
110
128
Eating
110
128
Driving
140
163
House keeping 150
175
Swimming
500
582
Running
900
1048
Biggest Downfalls
Experimental Procedure
Sometimes this metal and fiber bond isn’t the strongest, so it wears down and wears off through use. Another challenge, which is related, is that conductive fabric erodes over time.
Unique Properties
Improvement of Figure-of-Merit Sκ
Fabric offers the softness and malleability, and also having electrical properties.
Sometimes washable circuit is needed.
Fabric can be cut, sewn, stretched, crumpled and manipulated in other ways that hard metals, plastics cannot.
It has helped close the gap between fashion and engineering fields, making a new breed of fashion technologists.
Engineers are getting interested in how fabric behaves and best techniques for building with it.
Results and Discussion X-ray diffraction studies
X-ray photoelectron spectroscopy
Field Emission Scanning Electron Microscopy (FESEM) With EDX Mapping
In all the samples of ZnO/ Carbon fabric exhibited typical diffraction peaks of carbon at 25.8 . Whereas, the ZnO coated fabric showed three strong diffraction peaks at 31.67°, 34.12°, and 36.20° corresponding to (100), (002) and (101) planes of wurtzite ZnO respectively. All peaks of ZnO absolutely matched with JCPDS No. 36-1451. No impurity peaks were detected, which confirms that the carbon fabric were successfully deposited with ZnO nanostructures.
UV Shielding Properties
The photography of the pristine carbon fabric with ZnO before and after the growth of nanostructures is shown in Figure (a) and (b). In figure (c & d) it can be observed that the pure carbon fabric is in deep black color while the ZnO nanostructure coated carbon fabric is in white. The bare carbon fabric illustrates that each fiber with smooth surface has a uniform diameter of around 2µm. The obtained ZnO coating was partially covered on the fiber surface (fig. e, f, i, j) when small amount of hexamine was used. Hexamine offers the OH – ions to accelerate the reaction, initially less OH – ions existed in the solution when 1 M of hexamine was employed. On the other hand, some hexamine molecules would decompose at the reaction temperature of 120C, which would further decrease the number of OH – ions in the solution. All these factors would weaken the reducing ability of ZnOH and reduce the reaction rate, which lead to the decrease in density and incompleteness of the ZnO coatings. Moreover, (fig. g, h, k, l) the volume of hexamine used herein could increase the pH value of the solution, and the chemical reaction was found to proceed more quickly. As the pH value increased, the formation of nuclei and the subsequent crystal growth was enhanced and denser coatings were obtained. When the period of growth increased from 1h to 5h, a change of structure from nanorods to nanosheets was observed, which is the reason for the suppression effect observed along the c-axis direction at a prolonged time and growth was observed to be occurred in the longitudinal direction (due to many growth units around ZnO nuclei).
The XPS spectra of Zn 2p, and the peak positions of Zn 2p1/2 and Zn 2p3/2 locate at 1045.81 eV and 1022.93 eV. This shift observed at a higher binding energy with a value of 0.19 and 0.07 as a result of heat treatment. we can conclude that Zn is in the state of Zn2+. The O 1s peaks, due to its asymmetric shape, the peaks were deconvoluted into two peaks ( and ) using Gaussian fitting curve. The ‘’ peak was closely associated with the lattice oxygen of ZnO and ‘’ peak should be the evidence of oxygen vacancies within the ZnO matrix and the higher binding energy component is probably due to the presence of some surface hydroxyl species. This related study indicated that as discussed for the XRD analysis, there is no impurity spectra.
Electrical Properties
Thermal Stability
In general, two difference weight loss degradations appeared from the decomposition of fabric samples, a small weight loss due to primary removal of water at 160 C and major weight loss occurred at 460 C, can be attributed to the decomposition of amine groups. Moreover, TGA curves look similar to that of all coated ZnO carbon fiber with only difference is their residual percentages. The difference in residual percentages of ZnO carbon fabric materials as the zinc nitrate and hexamine precursor increases, the amount of ZnO deposition also increases upto certain weight percentage. This result indicated the lesser density coating availability of active sites in the carbon fiber surface, where ZnO starts to deposits in their higher loading.
Thermopower Properties
Figure (a) shows the time evolution of the measured temperatures in the high- and low- temperatures regions and the measured thermoelectromotive force (TEMF) for CFZ4 sample. The UPF value of bare carbon fabric (CF) shown the value of 28.62. Then ZnO coated carbon fabric shown the results could dramatically enhance the UV shielding property. In figure table given which shows the UV blocking efficiency with respect to UPF value and the better performance of the ZnO nanosheets is attributed to its morphology and denser coverage.
Significantly the results were found to be linear, indicating that the ohmic contact is very stable. The ZnO nanorods (CFZ1) of 2:1 concentration with 1 h showed the highest resistivity of 200 and ZnO nanosheets (CFZ4) of 1:2 concentrations with 5 h was, the better conduction of the fabric about 33 . However, the molar ratio of zinc nitrate and hexamine demonstrates the coated fabric did become higher when the denser nanosheets with high hexamine concentration, this is presumably due to smaller grain size resulted in closer spacing between sheets to sheets and more direct conduction pathway for generated electrons transfer.
In above Figure (b) shows the bar graph of thermopower value with and without ZnO coating. The absolute value of the thermopower was calculated by the linear fit between voltage (△V) and temperature difference (△T). The thermopower of ZnO coated on fabric was about -0.04 ~ 0.054 µV/K and for bare carbon fabric was found to be about 0.08 µV/K. It is important to note that carrier type was changed from P (before coating) to N-type (after ZnO coating) because more amount of ZnO was coated well on fabric. Thus, thermopower of ZnO on fabric was successfully obtained.
References
Conclusions
The thermopower is a thermoelectromotive force induced by the Seebeck coefficient in response to a temperature difference across the fabric and the resultant thermopower was estimated as a function of average temperature.
In this work, a simple, versatile, and effective approach for the development of ZnO on Carbon fabric prepared by solvothermal method was described. It was demonstrated that the coating of ZnO can convert from ‘P’ type into a ‘N’ type carbon fabric. The existence of nanosheets on the fabric surface caused an excellent UV shielding properties in ZnO 5 h processing time, as was demonstrated by an UPF value of 201.7. Additionally, the coated fabric showed good I-V characteristics with rectifying behavior of conductivity. Furthermore, we have investigated the thermopower of the coated fabric which attributes to the denser nanosheets of ZnO, possessing the highest value of 0.059 µV/K. 2D Nanostructures are good candidates for wearable device applications due to their relatively high thermopower and UV shielding.
1. S. J. Kim, J. H. We and B. J Cho, Energy Environ. Sci., 2014, 7, 1959. 2. Y. Wang, S. M. Zhang and Y. Deng, J. Mater. Chem. A., 2016, 4, 3554. 3. P. Veluswamy, S. Suhasini, F. Khan, A. Gosh, M. Abhijit, Y. Hayakawa and H. Ikeda, Carbohydr. Polym., 2017, 157, 1801. 4. Z. Zhan, J. An, Y. Wei, V. T. Tran and H. Du, Nanoscale, 9, 2017, 965. 5. V. Pandiyarasan, S. Suhasini, J. Archana, M. Navaneethan, A. Manjumdar, Y. Hayakawa and H. Ikeda, Appl. Surf. Sci., DOI 10.1016/j.apsusc.2016.12.202. 6. M. Hyland, H. Hunter, J. Liu, E. Veety and D. Vashaee, Appl. Energy, 2016, 182, 518. 7. M. K. Kim, M. S. Kim, S. Lee, C. Kim and Y. J. Kim, Smart Mater. Struct., 2014, 23, 105002. 8. F. Suarez, A. Nozariasbmarz, D. Vashaee and M. C. Ozturk, Energy Environ. Sci., 2016, 9, 2099.
Thank You !