Fabrication and characterization of Zn/MCM/Air Cell as humidity sensor /
Zn/MCM-41/air electrochemical cell, in the absence of electrolyte, revealed unique behaviour in response to ambient humidity variation. The cell's e.m.f. or open circuit voltage (OCV) was found responsive and distinctive to relative humidity content, which was in fact a novel transduction mecha...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
Kuala Lumpur :
Kulliyyah of Engineering, International Islamic University Malaysia,
2013
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| Subjects: | |
| Online Access: | Click here to view 1st 24 pages of the thesis. Members can view fulltext at the specified PCs in the library. |
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| Summary: | Zn/MCM-41/air electrochemical cell, in the absence of electrolyte, revealed unique behaviour in response to ambient humidity variation. The cell's e.m.f. or open circuit voltage (OCV) was found responsive and distinctive to relative humidity content, which was in fact a novel transduction mechanism for humidity sensing. The humidity sensing behaviour of the cell was attributed to the water absorption-desorption characteristics of the inorganic, mesoporous MCM-41 material. As the cell design merely comprised of three-layered structure, namely, metallic zinc, MCM-41 inorganic material and carbon, the present work was emphasized towards the microfabrication of a low cost, reliable Zn/MCM-41/air cell as humidity sensor. Anodic zinc layer was electrodeposited from a chloride bath onto a FR-4 printed circuit board substrate. MCM-41 material, prepared by sol-gel method, was coated onto zinc electrodeposits using spin coating technique. The cell structure was finally completed by applying carbon ink paste onto the MCM-41 membrane layer. These low cost processes were very much compatible with MEMS technology. The fabricated cell was ca. 40 m thick and 1 cm2 of circular shape. The resulting Zn/MCM-41/air cell as humidity sensor was characterized according to its linearity, hysteresis, repeatability, response and recovery time, durability and stability. The linear dependence of OCV on relative humidity was established above 0.9, although hysteresis was observed for humidity range 45-75 %RH. The dynamic sensing response between high (85 %RH) and low humidity (15 %RH) levels (repeatability profiles) of the cell was found compatible to commercial humidity sensor. T63 values for response and recovery were determined as 110 s and 245 s respectively, while the T90 values measured were 310 s and 378 s respectively. Upon exposure to ambient surrounding over a period of a month, the cell's humidity sensing measurement was still reliable, hence indicating its durability. In term of measurement stability, the readings fluctuation was around 26 mV which i.e. corresponded to 2.6 %RH, based on cell's sensitivity of 10 mV/%RH. The sensitivity can be increased by incorporating oxygen reduction catalyst such as manganese oxide in the carbon ink of the air electrode formulation, and subsequently reduces the fluctuation in humidity measurement. It was observed that the use of planar anodic zinc foil or even compact zinc electrodeposits led to the need of stabilization time prior to the cell being responsive to humidity variation. Finally, the discharge capacity of the Zn/MCM-41/air cell, in its 'dry' form, was investigated in view of its potential use as micropower source for smart active labels. It was discovered that the cell could deliver a discharge capacity of approximately 1 μAh under normal ambient surrounding with relative humidity of at least 57 %RH and temperature range of 23 - 28 ºC. |
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| Physical Description: | xiv, 96 leaves : ill ; 30cm. |
| Bibliography: | Includes bibliographical references (leaves 86-94). |