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What is the best way to design an electrochemical cell for optimal energy…
What is the best way to design an electrochemical cell for optimal energy output?
What is an electrochemical (Galvanic) cell?
A system which uses redox reactions to produce electricity.
Oxidation at the anode produces electrons and a metal ion. The electrons are carried through the solution to the salt bridge connecting the anode and cathode. The electrons arrive at the electrolyte around and cause the metal ions to reduce, attaching themselves to the cathode. This flow of electrons is a current, and they move due to a potential difference between the anode and the cathode.
What are the parts of an electrochemical cell?
Salt bridge
The salt bridge connects the two electrolytes by being placed with one end in each. The salt bridge is a piece of string (or other saturable connector) which is soaked in an electrolyte, typically a salt. The purpose of this electrolyte is to balance the charge in the electrolytes in the cells. The Salt bridge enables the transfer of electrons from the anode to the cathode, while also splitting the salt particles to balance charge in the other electrolytes.
Electrodes
Electrodes are metal strips which are placed in the electrolytes. They are made of solid metals, and are different metals. The more reactive of the metals will be the anode, which is where the oxidation reaction occurs, producing the electrons which cause the galvanic cell to function. The least reactive metal will become the cathode, and accepts the electrons produced by the anode, allowing the reactions to complete.
Electrolyte
Electrolytes consist of ions dissolved in an aqueous solution, typically water. The purpose of the electrolyte is to carry electrons between the electrodes. The electrolyte should contain an dissolved ionically bonded metals, such as metal sulphides, and should be of the same type of metal as the electrode they are surrounding, though it is not necessary.
How to measure energy output?
Current
Can be measured using an ammeter or a multimeter.
Voltage is proportional to current, meaning that the measurement of current can still be useful to understand.
Provides insight to where the batteries can be used (Considering fuses).
Current (I) is a measure of the rate of flow of electrons, measured in amps (A). Since electrons help to carry electrical energy around a circuit, a higher current means that more electrical energy is flowing through the circuit, representing a higher energy output. The current is produced in a galvanic by the electrons from the anode flowing towards the cathode. This is the process of the redox reactions, and is what makes a battery useful.
Voltage
Can be measured using a voltmeter, or a multimeter.
Effective choice of measurement as it is the main factor in the function of a battery, since it provides the force which moves the electrons.
Most useful to understand the efficiency of a battery.
Voltage (ΔV) is a measure of the difference in electrical potential energy, measured in volts (V) between two points on a circuit. In the case of the galvanic cell, the two electrodes are the points considered on the cell. A higher voltage means that more electrical energy flows through a system, meaning that higher voltage can be used to power more systems, and therefore is considered to be a better result in this experiment.
What affects an electrochemical cell?
Types of electrodes used
The types of electrodes used affects the rate at which oxidation occurs, and the amount of electrons lost during oxidation. This means that different metals used as the electrodes will result in different voltages produced.
Positives
Ideal types of electrodes used would be able to be used in a battery, meaning that results from this experiment could reasonably be transferred to the ideal function of a battery.
Negatives
Many different types of electrodes will be needed, increasing the material cost of the experiment.
Difficult to reasonably compare results.
Temperature
Temperature increases the rate of the redox reactions, meaning that more electrons flow through the wire, hence increasing current and voltage.
Positives
Has a significant and easily measurable impact on the voltage of the electrochemical cell.
Negatives
Potential safety risks if operating at high temperatures
Can be difficult to perform an experiment at a sufficiently large range of temperatures (to reduce impact of errors) with available equipment.
Batteries need to be able to operate at whatever temperature the equipment is at, meaning that this is not a useful factor to test.
Concentration of salt solution used in salt bridge
The concentration of salt in the salt bridge affects voltage by allowing the charge of the electrolyte to be balanced at different rates. A higher concentration of salt solution would mean that more ions can flow into the electrolytes, increasing the rate of transfer of electrons.
Positive
Easy to set up and use.
Altering the concentration present in the salt bridge would realistically be an effective change to a real battery, as it could be easily implemented.
Reduces material cost.
Negative
Would have minimal effect on the voltage produced.
Concentration of electrolytes
Increased concentration of electrolytes would mean that the oxidation reactions occur faster, hence increasing the rate of transfer of electrons.
Positives
Minimal effect on voltage means that lower concentrations can be used without a high loss in voltage, meaning that the cost of producing a battery could be decreased.
Easy to set up and test. High concentrations can be diluted and reused for the testing.
Effective to add to a real battery, as it does not occupy more space, reducing the cost of the production of a battery.
Negatives
Minimal effect on voltage, meaning that a random error could significantly affect the results.
The concentrations will change over time as the redox reactions occur, which reduces the accuracy of results if the same solution is reused for trials (to minimise cost).
Volume of electrolyte
Larger volumes of electrolyte mean that more ions are able to form, meaning that more electrons can flow through the system. This increases current, and therefore increases voltage.
Positives
Easy to set up and test.
Negatives
Has minimal effect if the surface contact area between electrode and electrolyte is constant, reducing the ability of this aspect to be appropriately tested.
An ideal battery would use minimal volumes to reduce cost.
Surface area of electrodes in contact with electrolyte
Redox reactions occur at the surface of the electrodes. Therefore larger surface area results in a faster rate of reactions.
Positives
Easy to test
Negatives
Surface area decreases on the anode while it increases on the cathode during the redox reactions. This could cause errors for successive trials.
Difficult to cut multiple strips to a precise surface area.
Dislodging of strip inside of electrolyte could cause change in surface area.
Batteries may need to be small, which reduces the potential surface area available.
Length of slat bridge in electrolyte
Salt bridge causes the charges in the electrolytes to remain balanced, allowing for the redox reactions to continue occurring.
Positives
Easy to prepare the salt bridges, as they can be measured an cut precisely, and can be held in salt solution to saturate the bridge.
Negatives
Will have minimal effect on the recorded voltage. May be negligible with some random errors.
Difficult to ensure the length of salt bridge in the electrolyte is the intended length for all trials, enabling significant random errors.
Difficult to ensure the amount of salt solution dissolved in the salt bridge
Battery may need to be small, meaning that the length of salt bridge in electrolyte may be restricted.
What was chosen
It was chosen to measure voltage as this is more useful to understand the efficiency and value of a battery, while also being easy to measure. The voltage is also what drives the function of the galvanic cell, as it forces the electrons to move from the anode to the cathode.
The concentration of electrolytes was chosen as it is an easy factor to adjust and test. The theoretical minimal difference in voltage produced with a lower concentration also means that the results of this experiment could be reasonably transferred to the production of a real battery with minimal cost.
How does changing the concentration of the electrolytes affect voltage produced by a galvanic cell?
What to measure
What to change
Final Question