Construction of a Solar Cell for Electrolyzing Water - Lab Report Example

Construction of a Solar Cell for Electrolyzing Water Introduction The significant role that energy plays in human life is undisputable. Despite the numerous uses of energy in industries, homes, and transportation for various purposes such as heating and lighting, most of the energy sources are non-renewable, and they are under threat due to over-exploitation (Bube 1). Thus, there is a need to develop alternative renewable sources of energy such as the solar. In this experiment, a solar cell would be constructed for conversion of sunlight energy into electrical power for use in electrolysis of water. Even though silicon cells are more efficient than solar cells in electrolyzing water, they are highly expensive. The solar cells are not only cheap, but they are also safe for the environmental use because they do not result in pollution. In electrolyzing water using solar energy, dye-sensitized photovoltaic cells are used. The sensitizer absorbs light that excites the chromophore leading to the production of electrons that undergo a series of processes within the cell to produce electric current for electrolyzing water. It is hypothesized that dyes or quantum dots can be used to sensitize the semiconductor oxide films of a solar cell to generate electricity (Gratzel 6841). Thus, this experiment aims to construct a dye-sensitized solar cell and to measure its current and voltage as well as using the cell to convert light into electricity for electrolysis of water. Materials and Reagents The materials required for this experiment included a multimeter for measuring resistance, a candle flame for producing carbon powder, and a piece of wire for connecting glass layers. Two pieces of glass and a piece of tissue paper are also required. The chemicals included ethanol for removing dirt on the surfaces of the glass, anthocyanin dye, titanium dioxide paste, potassium triiodide (KI3) electrolyte. In addition, a lab coat, goggles, and tongs were required for safety reasons. Experimental procedure We assembled the cell in the first lab session and determined the current and voltage. During this process, we identified the conducting side of a tin-oxide piece of glass by a multimeter and wiped off the surface with an ethanol-moistened tissue to remove dirt. We then added a small amount of titanium dioxide paste and heated the glass on a hot plate in a hood for 20 minutes until it turned green. On cooling to room temperature, we introduced anthocyanin dye. We coated the second piece of tin oxide glass with carbon powder by passing it through a candle flame. After which, we assembled the two glasses by putting the coated sides together and added few drops of the electrolyte, potassium triiodide solution (KI 3). We then illuminated the cell with light to determine the current and voltage and kept the cell for the next step. To electrolyze water, we rehydrated the cell by the electrolyte and assembled the electrolysis cell with a pipette bulb and exposed it to light for 20 minutes and measured voltage and current as well as making observations. We repeated the same process by connecting the cells from other groups both in series and parallel arrangements. Data and Results Data Sheet Name_______________________________________________________________________ Section_________________________________ Date_____________________________ Location:______________________________________________________________________ Sun Trial 1 Trial 2 Projector Trial 1 Trial 2 Voltage (V) 3.72 3.73 Voltage (V) 3.48 0.14 Current (A) 250 320 Voltage (V) 280 130 Power (Watt) 930 1193.6 Power (Watt) 974.4 18.2 Location _________ _________ Power (Watt) = Voltage (V) × Current (A) Therefore, Power for trials 1 and 2 both in sun and the overhead projector is equivalent to: For the sunlight; Trial 1, P= 3.72V × 250A = 930 W and Trial 2, P= 3.73V × 320A = 1193.6 W For the projector; Trial 1, P= 3.48V × 280A = 974.4 W and Trial 2, P= 0.14V × 130A = 18.2 W. When the solar cell was used to electrolyze water by exposing it to light, the solution at the bottom of the pipette bulb turned blue, and color intensified on more exposure to light. In addition, gas bubbles were produced during the process, and a black precipitate observed at the bottom of the cell. When the cells were connected in series, the solution gradually turned blue, and gas bubbles were observed. With time, the blue color intensified with precipitate forming at the bottom of the bulb. However, connecting the cells in a parallel arrangement resulted in a slow rate change of color after 2 minutes and no visible gas bubbles produced. There was also no precipitate formed by the time of completing the experiment. The series connection also gave a voltage and a current of 1.159V and 390A respectively. On the other hand, the parallel connection had a voltage of 0.286V and a current of 0.38 mA. From these recordings, the Power can be calculated as; Power = 1.159V × 390A = 452.01 W and 0.286 × 0.38 mA = 1.0868 × 10 -5 W for series and parallel connections respectively. Theoretically; The voltage for series arrangement is 1.088V and the lowest current is 0.22mA. Thus, the power = 1.088V × 0.22 mA = 2.3936 × 10 -4W. For parallel arrangement of 4 solar cells, the total voltage is 0.966V and the current is 0.72 mA. Thus, power = 0.966V × 0.72 mA = 0.96672 W. Discussions The constructed cell produced 3.72V, 250A and 3.73 V, 320A at trial 1 and trial 2 respectively on exposure to sunlight. When the cell was exposed to a projector, 3.48V and 280A were produced at trial 1 while trial 2 produced 0.14V and130A. Thus, the power of trial 1under sunlight and projectors was 930W and 974.4W respectively. Similarly, that for trial 2 is 1193.9W and 18.2W respectively. The best results were, therefore, achieved when the cells were exposed to sunlight. Replacing the dye by with materials of high-energy absorbing properties such as Perovskite mineral can improve the efficiency of the solar cell (Snaith 3623). In addition to absorbing ultraviolet radiation, Perovskite-sensitized cells can absorb infrared and visible light thus increasing efficiency. They are also cheaper compared to the dye-sensitized cells. During water electrolysis, I- ions are oxidized to I2 gas at the anode. The appearance of yellow-brown color solutions is observed due to the formation of triiodide ions (I3-). This reaction occurs as follows; I2 (aq) + I-(aq) I3-(aq). At the cathode, hydrogen in water is reduced to hydrogen that is seen as bubbles in the tube. Thus, the reactions; At the anode 2I-(aq) + 2e- I2 (g) At the cathode 2 H2O (l) + 2e- 2OH-(aq) + H2 (g) When the cells were connected together, intensity of the color increased and more gas was produced in a series connection than in parallel connection. It means that a series connection is more effective than parallel because of increased voltage across the series cells, thus producing more electrolysis. In order to maximize voltage, a series connection would be ideal because the terminal voltage is the combined voltages of individual cells. On the other hand, a parallel arrangement is required for maximum current because each cell adds to the total current in this arrangement. The dye is used to absorb the UV radiation to excite the electrons in the dye molecule which then pass through the semiconductor material titanium dioxide (cathode) to the carbon (anode) through the wire to the electrolyte and finally to the cathode. Electric current causing electrolysis of water is generated as a result of electron movement through the cell. The white titanium dioxide is not used on its own because it reflects light with very little absorbed, thus not effective. Reflection/Conclusions This experiment can be improved by reducing the inefficiencies that result from physical and chemical processes that affect electron flow through the wire. Materials that can absorb more light photons like the Perovskite would lead to more electrons produced, thus improving efficiency. Also, materials of longer duration and long working life would be desirable. Finally, this experiment has expanded my understanding of solar cells work by converting sunlight energy into electrical power. Works Cited Bube, Richard. Fundamentals of solar cells: photovoltaic solar energy conversion. Elsevier, 2012 Grätzel, Michael. "Solar energy conversion by dye-sensitized photovoltaic cells." Inorganic chemistry 44.20 (2005): 6841-6851 Snaith, Henry J. "Perovskites: the emergence of a new era for low-cost, high-efficiency solar cells." The Journal of Physical Chemistry Letters 4.21 (2013): 3623-3630 Read More