INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET)

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1 INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET) International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 ISSN (Print) ISSN (Online) Volume 4, Issue 6, September October 2013, pp IAEME: Journal Impact Factor (2013): (Calculated by GISI) IJARET I A E M E PHOTOCHEMICAL STUDY OF MICELLES IN PHOTOGALVANIC CELL FOR SOLAR ENERGY CONVERSION AND STORAGE A.S. Meena* 1, Rishikesh 2, Shribai 2 and R.C. Meena 2 * 1 Department of Chemistry, MLS University, Udaipur, Rajasthan (INDIA) Department of Chemistry, JNV University, Jodhpur, Rajasthan (INDIA) ABSTRACT Photochemical studies of micelles in photogalvanic cell containing Rhodamine 6G-EDTA- NaLS for solar energy conversion and storage. The observed cell performance in terms of photopotential, photocurrent, conversion efficiency, fill factor and storage capacity in terms of half change time are mv, µa, 1.26 %, and minutes on irradiation for minutes, respectively. The mechanism is proposed for the generation of photocurrent in photogalvanic cell. Keywords: - Photopotential, Photocurrent, Conversion Efficiency, Fill Factor, Storage Capacity. 1. INTRODUCTION The sun energy is the most readily available non-conventional source of energy which is most abundantly and freely available renewable source of energy. The new approach for renewable energy sources has led to an increasing interest in photogalvanic cells because of their reliable solar energy conversion and storage capacity. The photogalvanic cells are based on some chemical reaction, which rise to high- energy products on excitation by photons. This cell works on photogalvanic effect. The photogalvanic effect was first of all recognised by Rideal and Williams [1] and it was systematically studied by Rabinowitch [2-3], Potter and Thaller [4], Eliss and Kaiser [5], Rohatgi- Mukherjee et al. [6], Dixit and Mackay [7], and Kamet [8] studies various systems in photogalvanic cell for solar energy conversion and storage. Studies the performance of dye sensitized solar cells based on nanocrystals TiO 2 films prepared with mixed template method by Gratzel and Regan [9]. Optimum efficiency of photogalvanic cell for solar energy conversion has been studied by Albery and Archer [10]. Madwani et al., Gangotri and Meena, and Genwa and his coworkers [11-14] have been used of some reductant, photosensitizer and surfactant in photogalvanic cells for conversion of solar energy in to electrical energy. Gangotri and his co-workers [15-17] have been studied of photogalvanic cell for solar energy conversion and storage by using some dye with reductant, mixed dye, mixed reductant and dye with reductant and micelles. Recently, some photogalvanic cells were developed 17

2 on the basis of role of photosensitizer with reductant, photosensitizer with reductant and micelles for generation of electrical energy by Chandra [18], Chandra and Meena [19-20], Chandra et al. [21], Joseph et al. [22] and Meena et al. [23]. Present system is the effort to observe the photochemical study of micelles in photogalvanic cell containing Rhodamine 6G-EDTA-NaLS for solar energy conversion and storage. 2. EXPERIMENTAL METHODS Rhodamine 6G (MERCK), NaLS (LOBA), EDTA (MERCK) and NaOH (MERCK) were used in the present work. All the solutions were prepared in doubly distilled water and the stock solutions of all chemicals were prepared by direct weighing and were kept in coloured container to protect them from light. The whole system was set systematically for photogalvanic studies, which consists of thin foil of electrochemically treated platinum as electrode and saturated calomel electrodes as a reference electrode. The distance between the illuminated and dark electrode is 45 mm. An ordinary tungsten lamp of 200 W was used as light source. Water filter was used to cut-off IR radiations. The photopotetial was obtained as the difference between the initial potential of the system in dark and the equilibrium potential attained by the system under constant illumination. The potential was first measured in dark and the change in potential on illumination was measured as a function of time. The solution was bubbled with prepurified nitrogen gas for nearly twenty minutes to remove dissolved oxygen. Solutions of dye, reductant, micelles and sodium hydroxide were taken in an H-type glass tube. A platinum electrode (1.0 x 1.0 cm2) was immersed into one arm of H-tube and a saturated calomel electrode (SCE) was kept in the other. The whole system was first placed in dark till a stable potential was obtained and then, the arm containing the SCE was kept in the dark and the platinum electrode was exposed to a 200 W tungsten lamp. A water-filter was used to cut off infrared radiations. The photochemical bleaching of Rhodamine 6G was studied potentiometrically. A digital ph meter (Systronics Model-335) and a microammeter (Ruttonsha Simpson) were used to measure the potential and current generated by the system, respectively. The current voltage characteristics of photogalvanic cell have been studied by applying an external load with the help of a carbon pot (log 470 K) connected in the circuit through a key to have close circuit and open circuit device. The experimental set-up of photogalvanic cell is given in Figure 1. The effect of variation of different parameters has also been observed. The rate of change in potential after removing the source of illumination was 0.93mV min -1 in Rhodamine 6G-EDTA-NaLS. Figure-1 Experimental set-up of photogalvanic cell 18

3 3. RESULTS AND DISCUSSION 3.1. EFFECT OF VARIATION OF DYE (RHODAMINE 6G) CONCENTRATION ON THE CELL It was observed that the photopotential and photocurrent were increased with the increase in concentration of the dye. A maximum was obtained for a particular value of Rhodamine 6G concentrations, above which a decrease in the electrical output of the cell was obtained. The reason of the change in electrical output is that lower concentration of photosensitizer resulted into a fall in electrical output because fewer photosensitizer (Rhodamine 6G) molecules are available for the excitation and consecutive donation of the electrons to the platinum electrode whereas the higher concentration of photosensitizer (Rhodamine 6G) again resulted into a decrease into electrical output as the intensity of light reaching the dye molecules near the electrode decrease due to absorption of the major portion of the light by dye molecules present in the path. The results are given in Table EFFECT OF VARIATION OF REDUCTANT (EDTA) CONCENTRATION ON THE CELL The photopotential and photocurrent were found to increase with the increase in concentration of the reductant [EDTA], till it reaches a maximum. On further increase in concentration of EDTA, a decrease in the electrical output of the cell was observed. The reason of the change in electrical output is that the lower concentration of reducing agent resulted into a fall in electrical output because fewer reducing agent molecules are available for electron donation to photosensitizer (Rhodamine 6G) molecule whereas the higher concentration of reducing agent again resulted into a decrease in electrical output, because the large number of reducing agent molecules hinders the dye molecules from reaching the electrode in the desired time limit. The results are given in Table EFFECT OF VARIATION OF MICELLES (NALS) CONCENTRATION ON THE CELL The effect of variation of (NaLS) was investigated in Rhodamine 6G EDTA NaLS system. It was observed that electrical output of the cell was found to increase on increasing the concentration of micelles reaching a maximum value. On further increase in their concentrations, a fall in photopotential, photocurrent and power of the photogalvanic cell was observed. The reason of the change in electrical output is that the micelles solubilize the dye molecules up to highest extent at or around their micelles concentration. The results are given in Table EFFECT OF VARIATION OF PH ON THE CELL The effect of variation in ph on photoelectric parameters of cell is studied. It is found that the cell containing Rhodamine 6G-EDTA-NaLS to be quite sensitive to the ph of the solution. It is observed that there is an increase in the photoelectric parameters of this cell with the ph value (In the alkaline range). At ph a maxima is obtained. On further increase in ph, there is a decrease in photoelectric parameters. It is observed that the ph for the optimum condition has a relation with pka of the reductant and the desired ph is higher than in pka value (ph>pka). The reason of the change in electrical output is that the availability of the reductant in its anionic form, which is a better donor form. The above same is reported in Table EFFECT OF DIFFUSION LENGTH AND ELECTRODE AREA ON THE CELL The effect of variation in diffusion length (distance between the two electrodes) on the photoelectric parameters of the cell (i max, i eq and initial rate of generation of photocurrent) is studied using H-shaped cells of different dimensions. The effect of electrode area on the photoelectric parameters of the cell is also reported here. It is observed that both i max and rate of change in initial 19

4 generation of photocurrent (µa min -1 ) increase with respect to the diffusion length whenever the equilibrium photocurrent (i eq ) shows a small decrease with respect to the diffusion length. The reason of the change in electrical output is that the main electroactive species are the leuco or semi-leuco form of dye (photosensitizer) and the dye in illuminated and dark chamber respectively. The reductant and its oxidation product act only as electron carriers in the path. The rate of change in photoelectric parameters with respect to the diffusion length is graphically presented in Table 2. Similarly, Table 3 shows rate of change in photoelectric parameter with respect to electrode area. It is found that the maximum photocurrent show increasing fashion with electrode area whereas the equilibrium photocurrent (i eq ) show decreasing fashion. Table-1: - Effect of concentration (Rhodamine 6G, EDTA and NaLS) and ph on the cell Parameters Photopotential (mv) Photocurrent (µa) Power (µw) (Rhodamine 6G) 10-5 M (EDTA) 10-3 M (NaLS) 10-3 M ph

5 Diffusion Length D L (mm) Table-2: - Effect of diffusion length Maximum photocurrent i max (µa) Equilibrium photocurrent i eq (µa) Rate of initial generation of photocurrent (µa min -1 ) Table-3: - Effect of electrode area Rhodamine 6G-EDTA-NaLS Electrode area (cm 2 ) Maximum photocurrenti max (µa) Equilibrium photocurrenti eq (µa) EFFECT OF TEMPERATURE AND LIGHT INTENSITY ON THE CELL The effect of temperature on the photoelectric parameters of the cell is studied. The effect of light intensity on the photoelectric parameters of the cell also investigated here. It is observed that the photocurrent of the photogalvanic cell is found to be increased with the temperature whereas the photopotential is decreased. Thereafter, the effect of temperature on total possible power output in the Rhodamine 6G-EDTA-NaLS cell is also studied and it is observed that there a linear change between the both. The reason of the change in electrical output is that internal resistant of the cell decreases at higher temperature resulting into a rise in photocurrent and correspondingly, there will be a fall in photopotential. The same is presented in Figure 2. Similarly, Figure 3 shows rate of change in photoelectric parameter with respect to light intensity. The light intensity is measured in terms of mwcm -2 with the help of solarimeter (CEL Model SM 203). It is found that the photocurrent show linear increasing fashion with light intensity whereas the photopotential show an increment in a logarithmic fashion. 21

6 Figure-2 Variation of photopotential and photocurrent with Temperature Figure-3 Variation of photocurrent and log V with light intensity 22

7 3.7. CURRENT-VOLTAGE (I-V) CHARACTERISTICS OF THE CELL: The short circuit current (i sc ) and open circuit voltage (V oc ) of the photogalvanic cells are measured with the help of a multimeter (keeping the circuit closed) and with a digital ph meter (keeping the other circuit open), respectively. The current and potential values in between these two extreme values are recorded with the help of a carbon pot (log 470 K) connected in the circuit of Multimeter, through which an external load is applied. The current-voltage (i-v) characteristics of the photogalvanic cells containing Rhodamine 6G-EDTA-NaLS cell is graphically shown in Figure 4. Figure-4 Current-Voltage (i-v) Curve of the Cell 3.8. STORAGE CAPACITY AND CONVERSION EFFICIENCY OF THE CELL: The storage capacity (performance) of the photogalvanic cell is observed by applying an external load (necessary to have current at power point) after terminating the illumination as soon as the potential reaches a constant value. The storage capacity is determined in terms of t 1/2, i.e., the time required in the fall of the output (power) to its half at power point in dark. It is observed that the cell can be used in dark for minutes on irradiation for minutes. So the observed storage capacity of the cell is %. The results are graphically presented in Figure 5. The conversion of the efficiency of the cell is determined as 1.265% with the help of photocurrent and photopotential values at the power point and the incident power of radiations by using the formula V pp x i pp Fill factor (η) = (1) V oc x i sc V pp x i pp Conversion Efficiency = x100% (2) 10.4 mw 23

8 Figure-5 Performance of the Cell 3.9. PERFORMANCE OF THE CELL The overall performance of the photogalvanic cell is observed and reached to remarkable level in the performance of photogalvanic cells with respect to electrical output, initial generation of photocurrent, conversion efficiency and storage capacity of the photogalvanic cell. Table 4 shows the results are obtained in Azur B-EDTA-CTAB cell. Table-4:- Performance of the cell S. No. Parameter Observed value 1. Dark potential mv 2. Open circuit voltage (V OC ) mv 3. Photopotential (DV) mv 4. Equilibrium photocurrent (i eq ) ma 5. Maximum photocurrent (i max ) ma 6. Initial generation of photocurrent 25.5 ma min Time of illumination min 8. Storage capacity (t 1/2 ) min 9. % of storage capacity of cell % 10. Conversion efficiency % 11. Fill factor (η)

9 4. MECHANISM On the basis of these observations, a mechanism is suggested for the generation of photocurrent in the photogalvanic cell as: 4.1. ILLUMINATED CHAMBER Dye hν Dye* (3) Dye* + R Dye (Semi or leuco) + R (4) AT PLATINUM ELECTRODE: Dye Dye + e (5) 4.2. DARK CHAMBER AT CALOMEL ELECTRODE: Dye + e - Dye (Semi or leuco) (6) Dye + R + Dye + R (7) Where Dye, Dye*, Dye, R and R + are the dye, excited form of dye, semi or leuco form of dye, reductant and oxidized form of the reductant, respectively. 5. CONCLUSION On the basis of the results, it is concluded that micelles (NaLS) with reductant (EDTA) and dye (Rhodamine 6G) can be used successfully in a photogalvanic cell. The conversion efficiency and storage capacity of the cell is 1.26% and minutes respectively, on irradiation for minutes developed photogalvanic cell. It has been observed that the micelles have not only enhanced the electrical parameters (i.e. photopotential, photocurrent and power) but also the conversion efficiency and storage capacity of photogalvanic cell. Photogalvanic cells can be used in dark whereas photovoltaic cells cannot be used in dark. Photogalvanic cells have better storage capacity than photovoltaic cells. So photogalvanic cells showed good prospects of becoming commercially viable. NOMENCLATURE i eq = photocurrent at equilibrium i max = maximum photocurrent i pp = photocurrent at power point i sc = short circuit current ml = milliliter mv = millivolt M = molarity pp = power point t 1/2 = storage capacity of cell DV = observed photopotential V oc = open circuit voltage V pp = photopotential at power point η = fill factor ma = microampere mw = microwatt 25

10 ACKNOWLEDGEMENT The authors are grateful to The Head, Department of Chemistry, MLS University, Udaipur, Rajasthan (INDIA) for providing the necessary laboratory facilities to conduct this research work. One of the authors (A.S.Meena) is thankful to Ministry of New and Renewable Energy (MNRE), Government of India, New Delhi (INDIA) for the financial assistance to this research work. REFERENCES [1] Rideal.E.K and Williams.E.G (1925), J. Chem. Soc. FaradayTrans., 127, [2] Rabinowitch.E (1940), J. Chem. Phys., 8, [3] Rabinowitch.E (1940), J. Chem. Phys., 8, [4] Potter.A.E and Thaller.L.H (1959), Solar Energy, 3, 1-7. [5] Eliss.A.B and Kaiser.S.D (1976), J. Am. Chem. Soc., 98, [6] Rohatgi-Mukherjee.K.K, Roy.M and Bhowmik.B.B (1983), Solar Energy, 31, [7] Dixit.N.S and Mackay.R.A (1982), J. Phys. Chem., 86, [8] Kamat.P.V (1985), J. Chem. Soc., Faraday Trans., 1, [9] Gratzel.M and Regan.B.O (1991), Nature, 353, [10] Albery.W.J and Archer.M.D (1977), Nature, 270, [11] Madhwani.S, Vardia.J, Punjabi.P.B and Sharma.V.K (2007), J. Power and Energy: Part A, 221, [12] Gangotri.K.M and Meena.R.C (2001), J. Photochem. Photobio. A. Chem., 141, [13] Genwa.K.R and Khatri.N.C (2006), Int. J. Chem. Sci., 4, [14] Genwa.K.R, Kumar.A and Sonel.A (2009), Applied Energy, 86(9), [15] Gangotri.K.M and Indora.V (2010), Solar Energy, 84, [16] Gangotri.K.M and Bhimwal.K.M (2011), Energy Sources, Part A, 33, [17] Bhati.K.K and Gangotri.K.M (2011), Int. J. Elect. Power & Energy Systems, 33, [18] Chandra.M (2012), Res. J. Pharm. Biological & Chemical, 3(2), [19] Chandra.M and Meena.R.C (2010), Int. J. Chemical Sciences, 8(3), [20] Chandra.M and Meena.R.C (2011), J. Chem. & Pharm. Research, 3(3), [21] Chandra.M, Singh.A and Meena.R.C (2012), Int. J. Physical Sciences, 7(42), [22] Joseph.A, Nagarajan and Mary.A (2013), Int. J. Electrical Engineering & Technology (IJEET), 4(4), [23] Meena.A.S, Meena.P.L, Chandra.M, Meena.R, Shribai and Meena.R.C (2013), Int. J. Electrical Engineering & Technology (IJEET), 4(4),