Plant leaf as a new battery material.
The plant leaves are natural bio-system which contains numerous inorganic and organic ions, obtained from soil and others is synthesized by plant cells (Weil, 1986; Ray & Fritz, 1992). Presence of ions in the system gives an immediate impression of an electrolytic behavior. But due to the controls exerted by the living systems, it does not remain a simple physical electrolytic system. They defined as "bioelectrolytic systems or "bio-ionic conducting systems" and may act as new non-conventional source of energy.
The presence of ions plays an important role in transporting energy to various parts of the plant. In the bio-systems, ionic motion is controlled and regulated by the physiological activities of living cell and the energy in it is stored in bio-chemical or chemical form, from sun and biotic environment. It is, therefore quite likely that the electrical energy produced from the battery or emf-device developed from bio-systems may have galvanic as well as bio contribution. This is clear from the studies of bio-electro-potential (BEP) of plants (Gensler, 1978; Goldstein & Gensler, 1981).
Further the living biological systems generate bio-electricity through enzyme catalyzed reactions working on redox principles for their body organization (Lehninger, 1970; Hope, 1971; Nobel, 1974). The processes like photosynthesis (Tien, 1972), respiration (Mitchell, 1966), injury and healing (Gensler, 1978, 1979, 1980) are electrical origin. Though the amount of bio-electropotential (BEP) is very small, it can be suitably exploited in the changing scenario of today's electronic world. One of the methods tried is the development of Bio-emf-devises (BEDs) i.e. Bio-batteries.(Jain et al, 1987,1988,1989,1990, Hundet,1994).
The low power bio-emf-devices (BEDs) have been developed using plant leaves. The BEDs are like the primary electrochemical cells where an ionic conductor (Electrolyte) is sandwiched between two electrodes. In the BED the leaf acts as an electrolytic material, but the involvement of some biological phenomena, it differs from physical electrolytic. Energy produced from BEDs has voltaic as well as biological origin.(Jain et al 1988;Hundet,1994). The plant leaves as new non-conventional material is hear by used for developing Biobatteries, because it is an important source of energy for highly used low power consuming micro-electronic gadgets. In this paper various factor for selection of leaf are discussed.
MATERIALS AND METHODS
Following plant leaves have been selected for the experiment:
(1) Opuntia and
The mature leaf is plucked from a plant and washed with distilled water then the epidermis of leaf was removed from both sides. This processed leaf is then used to construct a unit of Bio-emf-device. A single unit is constructed by sandwiching a processed leaf between the graphite and magnesium electrodes. This system is kept intact by applying a small positive pressure for the uniform surface contact with leaf. This whole system is called Bio-emf-device or BED. The electrical connections were made for the circuit connection. This single unit of BED is used for experimental purpose.
The number of living cell per unit area of the leaf has been counted by a research microscope. The Open Circuit Voltage (OCV) and Short Circuit Current (SCC) of BEDs have been made using graphite and magnesium electrode pair of size-1sq.cm. under normal atmospheric conditions, after 15 minutes of the fabrication of the BEDs. This is done because the OCV value of BEDs has attained a steady value.
The electrical measurements have been made using HIL-2201 series digital panel meters and MIC-16 H Multimeter. DC voltage measurements were made using 2201/02 model which have resolution of 1mV and an accuracy of ?(0.1% rdg+1 dgt), DC current measurements arranged by 2201/12/1 have resolution of 1[micro]A and have an accuracy of [+ or -](0.25% rdg[+ or -]1 dgt).
RESULTS AND DISCUSSIONS
Basic battery evaluation needs essentially the study of the performance indices like Open circuit voltage, Short circuit current, Maximum power ([P.sub.max]), Internal resistance, Useful energy density, Time to reach cut off voltage etc. These indices are obtained by studying the CurrentVoltage, Current-power and Discharge characteristics of the BEDs (Figure-1). The physical and battery parameters of leaves are presented in the table-1.
From the table, it is seen that the short circuit current density of BED made using Opuntia is higher than Yucca-aloifolia-BED. Yucca-aloifolia has more number of living cells than the Opuntia. Opuntia, which is modified stem, act as a leaf, because leaf of Opuntia modified in spines, therefore here consider it as a succulent leaf, containing mesophyll cells and organic acids while Yucca-aloifolia leaf is non-succulent containing palisade type cells.
In the succulent plant leaf, there is more air space between cells, which help in respiration (Datta,1980). The respiratory quotient of succulent plant is more than the other plants therefore, more electrons are comparatively released. While in a non-succulent plant leaf, there is less air space between the cells, which results in less respiration. In this type of leaf mechanical tissues and latex are present which also reduces the effective number of cell participating in the respiration.
This may be the reason that BED prepared using Yucca-aloifolia gives less short circuit current value than the Opuntia.
CHARACTERISTICS OF BEDS
A linear relation between Dry/Wet Ratio and Time to reach cut-off voltage has been obtained. Thickness is also an important factor in this context. Thicker leaf Opuntia (1525mm) has better life 398hrs than the life 176hrs of thin leaf Yucca-aloifolia (254mm), this explaining why the leaves Opuntia -BED gives long service than the Yucca-aloifolia-BED.
Maximum power was obtained 660[micro]W from Opuntia--BED, while Yucca-aloifolia-BED gives 511 [micro]W. The useful energy density of Opuntia--BEDs was obtained 15.87W.hr/[mt.sup.2], while from Yucca-aloifolia-BED was 4.41 W.hr/[mt.sup.2]. The internal resistance was found between 0.8 to 6 k[OMEGA].
Results indicate that Opuntia -BED is found more suitable in terms of power, useful energy density, time to reach cut off voltage than the Yucca-aloifolia-BED.
On the basis of experimental results, it is concluded that practically any leaf can be used to develop BEDs. Succulent plant leaves containing mesophyll cells and organic acid having more air space between cells, help in respiration. The respiratory quotient of succulent plant is more than the other plants, On the other hand non-succulent leaf contain more number of living cell but less air space between cells is marked by absence of organic acid thereby reducing the respiration. Respiration seems to be an important factor for generation of electrical energy from plant leaf. Therefore succulent plant leaf gave better results.
This suggests that battery made using plant leaves can be considered as a new type of Bio-fuel-cell. Here, stored food is utilized by the living cell for their survival and the presence of electrodes seems to be responsible for breaking the respiratory chain.
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Bharat Mishra, Ravindra Singh, S.K. Tripathi and S.K. Chaturvedi
Bio-Physics Lab, Mahatma Gandhi Chitrakoot Gramodaya Viswavidyalaya, Chitrakoot, Satna (M.P.)-485331
Table 1: Physical parameters of the leaves & various performance indices of the BEDs (electrode:C-Mg,) Parameters Name of leaf Opuntia Yucca-aloifolia Appro. Thickness 1525 mm 254 mm of leaf Weight of Leaf 1260 mg/sq. cm. 139 mg/sq. cm. Dry/wet Ratio 0.085 0.291 Leaf type Succulent Non succulent Cell type Mesophyll Palisade Surface cell 200 [+ or-] 30 900 [+ or -] 100 density (/sq.mm) Open circuit 1750 [+ or -] 50 mV 1605 [+ or -] 50 mV voltage (/sq.cm) Short circuit 1750 [+ or -] 50 [micro]A 1600 [+ or -] 50 current (/sq.cm) [micro]A Maximum Power 660[micro]W 511[micro]W ([P.sub.max]) Current 1035 mA 749 [micro]A corresponding to [P.sub.max] Internal 0.8-6 k[OMEGA] 1-3 [micro]W resistance Time to reach 398hrs 176hrs cut off voltage Useful energy 15.87 W.hr/[m.sup.2] 4.41 W.hr/[m.sup.2] density
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|Author:||Mishra, Bharat; Singh, Ravindra; Tripathi, S.K.; Chaturvedi, S.K.|
|Publication:||Bulletin of Pure & Applied Sciences-Botany|
|Date:||Jan 1, 2006|
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