Discussion Examples for Fuel Cell Experiments | Voltage Drop, Electrode Reactions, and Efficiency

What Is a Fuel Cell Experiment?

A fuel cell experiment is an experiment in which electrical energy is obtained using a chemical reaction between a fuel and an oxidizing agent.
Ordinary batteries generate electricity by consuming reactants stored inside them, whereas fuel cells can continue generating electricity as long as fuel and oxygen are continuously supplied from outside.
In a hydrogen fuel cell, hydrogen is used as the fuel and oxygen as the oxidizing agent, with water produced as the product.

Fuel cells are characterized by extracting the electron transfer of a redox reaction into an external circuit rather than converting chemical energy into heat energy through combustion.
Therefore, they have high energy-conversion efficiency and are attracting attention as a clean power-generation method because the main product during power generation is water.
In experiments, performance is evaluated by measuring voltage, current, load resistance, power-generation time, fuel consumption, and other quantities.

Main Items to Include in the Results

In the results of a fuel cell experiment, organize the type of fuel cell, type of fuel, oxidizing agent, electrolyte, electrode material, open-circuit voltage, voltage under load, current, output, power-generation time, voltage change over time, fuel consumption, efficiency, and other information.
To discuss voltage drop and efficiency, it is important to clearly record the load conditions and measurement time.

Main Items to Include in the Results

• Type of fuel cell
• Type of fuel
• Type of oxidizing agent
• Type of electrolyte membrane or electrolyte solution
• Electrode material
• Presence or absence of a catalyst
• Open-circuit voltage
• Load resistance
• Voltage under load
• Current value
• Output
• Change in voltage over time
• Fuel-supply conditions
• Oxygen-supply conditions
• Condition of generated water
• Fuel consumption
• Power-generation efficiency
• Causes of error and points for improvement

Reference Experimental Values and Calculation Examples for Fuel Cell Experiments

Here, the open-circuit voltage, voltage drop under load, current, output, and efficiency of a fuel-cell power-generation experiment using hydrogen and oxygen are organized using reference experimental values.

In a fuel cell, electrical energy is extracted through the oxidation of hydrogen and the reduction of oxygen.
Although a high voltage can theoretically be obtained, in actual measurements the voltage may be lower than the theoretical value because of internal resistance, delays in electrode reactions, fuel supply, and resistance of the membrane or electrolyte.

Reference Experimental Conditions

Confirmation of Electrode Reactions

In a hydrogen fuel cell, hydrogen is oxidized at the negative electrode and oxygen is reduced at the positive electrode.
Overall, water is produced from hydrogen and oxygen, and electrical energy is extracted in the process.

Open-Circuit Voltage and Voltage Under Load

First, the voltage when no load is connected to the external circuit is defined as the open-circuit voltage.
Next, a resistor is connected and the voltage is measured while current flows.

Example Calculation of Current

The current when a resistor is connected can be determined using Ohm’s law.

Current I = Voltage V ÷ Resistance R

For example, when a 50 Ω resistor is connected and the measured voltage is 0.82 V, the current is as follows.

I = 0.82 V ÷ 50 Ω = 0.0164 A

In other words, under the condition where a 50 Ω load was connected, a current of approximately 16.4 mA flowed.

Example Calculation of Output

The electric power supplied by the fuel cell to the external circuit can be determined from the product of voltage and current.

Output P = Voltage V × Current I

Under the 50 Ω condition, the voltage is 0.82 V and the current is 0.0164 A, so the output is as follows.

P = 0.82 V × 0.0164 A = 0.0134 W

Therefore, the output under this condition is approximately 0.013 W.

Relationship Between Load Resistance and Voltage Drop

The open-circuit voltage was 0.96 V, but when a load was connected and current flowed, the measured voltage decreased.
In particular, as the load resistance became smaller and the current increased, the voltage drop became larger.

Example Calculation of Voltage-Drop Percentage

The voltage-drop percentage expresses as a percentage how much the voltage decreases under load relative to the open-circuit voltage.

Voltage-drop percentage (%) = (Open-circuit voltage − Voltage under load) ÷ Open-circuit voltage × 100

Under the 20 Ω condition, the open-circuit voltage is 0.96 V and the voltage under load is 0.68 V, so it can be calculated as follows.

Voltage-drop percentage = (0.96 − 0.68) ÷ 0.96 × 100 = 29.2%

This result shows that when a 20 Ω load was connected, the voltage decreased by approximately 29.2% relative to the open-circuit voltage.

Relationship Between Current and Output

When the load resistance decreases, the current increases, but the voltage decreases.
Therefore, output does not necessarily increase simply because the current becomes larger, and is determined by the balance between voltage and current.

In this reference example, the largest output was obtained under the 10 Ω condition.
However, if the load is reduced further, the current may increase while the voltage decreases greatly, causing the output to decrease.
A fuel cell is therefore considered to have a load condition at which the output becomes maximum.

Example Efficiency Calculation Using Fuel Consumption

When considering fuel-cell efficiency, the electrical energy extracted is compared with the chemical energy possessed by the hydrogen.
Here, an example is considered in which electricity is generated for 60 seconds with a 20 Ω load connected.

First, the extracted electrical energy is determined by multiplying the output by the time.

Electrical energy = Output × Time

0.0231 W × 60 s = 1.39 J

Next, the efficiency is determined by dividing the extracted electrical energy by the supplied chemical energy.

Efficiency (%) = Electrical energy ÷ Chemical energy × 100

Efficiency = 1.39 J ÷ 2.10 J × 100 = 66.2%

Therefore, in this reference example, an efficiency of approximately 66.2% was obtained under the 20 Ω condition.

Comparison Between Air Supply and Oxygen Supply

The voltage and output obtained may differ depending on whether air or oxygen is used as the oxidizing agent.
The higher the oxygen concentration, the more readily the oxygen-reduction reaction proceeds at the positive electrode, and the voltage drop may become smaller.

In this reference example, the voltage and output were larger when oxygen was supplied than when air was supplied.
This was considered to result from sufficient oxygen supply at the positive electrode, making the oxygen-reduction reaction proceed more readily.

Example of How to Write the Results

The open-circuit voltage of the fuel cell was 0.96 V.
When a 100 Ω load was connected, the voltage was 0.88 V, the current was 0.0088 A, and the output was 0.0077 W.
When the load resistance was decreased, the current increased, but the voltage decreased, and under the 10 Ω condition the voltage decreased to 0.50 V.

Under the condition where a 20 Ω load was connected, the voltage was 0.68 V, the current was 0.0340 A, and the output was 0.0231 W.
Compared with the open-circuit voltage of 0.96 V, the voltage-drop percentage was 29.2%.
In addition, the electrical energy generated over 60 seconds was 1.39 J, and when the chemical energy of the consumed hydrogen was assumed to be 2.10 J, the efficiency was calculated to be 66.2%.

Points for Connecting the Results to the Discussion

In a discussion of a fuel cell experiment, it is important not only to list voltage and current values but also to explain why the voltage decreases when a load is connected and under which conditions the output becomes large.

• Was there a difference between the open-circuit voltage and the voltage under load?
• When the load resistance was decreased, did the current increase and the voltage decrease?
• Was there a load condition at which the output became maximum?
• Can internal resistance, delays in electrode reactions, and insufficient fuel supply be considered as causes of voltage drop?
• Was there a difference in voltage or output between air supply and oxygen supply?
• When calculating efficiency, were the electrical energy and chemical energy of the fuel compared?
• Could hydrogen leakage, wetting of the electrodes, poor contact, or the internal resistance of the measuring instrument have been sources of error?

Example Discussion

In this experiment, the open-circuit voltage of the fuel cell was 0.96 V, but the voltage decreased when a load was connected.
The voltage was 0.88 V with a 100 Ω load, whereas it decreased to 0.50 V with a 10 Ω load.
This was considered to result from the smaller load resistance causing a larger current to flow, thereby increasing voltage losses due to resistance inside the fuel cell and delays in electrode reactions.

On the other hand, when the load resistance was decreased, the current increased and the output also increased.
In this reference example, the output under the 10 Ω condition was 0.0250 W, the largest among the measured conditions.
However, if an even larger current were extracted, the voltage drop could become greater and the output could decrease.
Therefore, a fuel cell is considered to have an optimum load condition determined by the balance between voltage and current.

In addition, the voltage and output were larger when oxygen was used as the oxidizing agent than when air was used.
This was considered to result from the higher oxygen concentration making the oxygen-reduction reaction at the positive electrode proceed more readily and reducing the voltage loss associated with the reaction.
This indicates that fuel-cell performance is also greatly affected by the supply conditions of fuel and oxygen.

Regarding efficiency, when the electrical energy generated for 60 seconds under the 20 Ω condition was 1.39 J and the chemical energy of the consumed hydrogen was 2.10 J, the efficiency was 66.2%.
In practice, not all of the supplied chemical energy can be extracted as electrical energy because of heat generation, internal resistance, reaction overvoltage, unused fuel, and other losses.
Therefore, when discussing efficiency, it is important to specifically describe the causes of energy loss rather than only the difference from the theoretical value.

Summary

In a fuel cell experiment, the power-generation characteristics and causes of voltage drop can be discussed by measuring the open-circuit voltage, voltage under load, current, and output.

In this reference example, the current increased as the load resistance decreased, but the voltage decreased.
In addition, the output was larger when oxygen was supplied than when air was supplied.
In a report, it is useful to relate electrode reactions, internal resistance, fuel supply, oxygen supply, and energy-conversion efficiency.

Principle of a Hydrogen Fuel Cell

In a hydrogen fuel cell, hydrogen H2 is oxidized at the fuel electrode, producing electrons and protons H+.
The electrons flow through the external circuit to the oxygen electrode, and this flow is used as electric current.
The protons move through the electrolyte membrane to the oxygen electrode, where they react with oxygen and electrons to produce water H2O.

In this way, a fuel cell separates the reaction of hydrogen and oxygen at the electrodes and extracts the electron transfer through an external circuit.
The overall reaction is the same as the combustion reaction of hydrogen, in which H2 and O2 form H2O.
However, unlike combustion, the important point is that the chemical energy is converted directly into electrical energy.

Fuel electrode: H2 → 2H+ + 2e-

Oxygen electrode: 1/2O2 + 2H+ + 2e- → H2O

Overall: H2 + 1/2O2 → H2O

Reaction at the Fuel Electrode

At the fuel electrode, an oxidation reaction occurs in which hydrogen loses electrons.
Hydrogen molecules H2 react on the catalyst surface and separate into protons H+ and electrons e-.
The protons move through the electrolyte membrane or electrolyte, while the electrons flow into the external circuit.

If the reaction at the fuel electrode is slow, the voltage and current of the entire fuel cell decrease.
Catalyst activity, electrode surface area, hydrogen supply, degree of electrode wetting, and contact with the electrolyte affect the reaction rate.
The fuel electrode is an important location where the chemical energy of the fuel is converted into a flow of electrons.

Reaction at the Oxygen Electrode

At the oxygen electrode, a reduction reaction occurs in which oxygen accepts electrons.
Electrons arriving through the external circuit from the fuel electrode and H+ transported through the electrolyte react with oxygen O2 to produce water.
In a hydrogen fuel cell, this oxygen-reduction reaction tends to be a major cause of voltage loss.

The oxygen-reduction reaction is generally slower than the hydrogen-oxidation reaction.
Therefore, catalysts such as platinum may be used.
If the oxygen supply is insufficient or generated water blocks the electrode surface, the oxygen-electrode reaction becomes more difficult and the voltage decreases.

1/2O2 + 2H+ + 2e- → H2O

Open-Circuit Voltage and Voltage Under Load

Open-circuit voltage is the voltage measured under conditions in which almost no current flows through the external circuit.
It is treated as a value close to the theoretical electromotive force of the fuel cell, but in practice it may be lower than the theoretical value because of gas leakage, fuel crossover, mixed potentials on catalyst surfaces, and other factors.

When a load is connected, current flows and the voltage becomes lower than the open-circuit voltage.
This is because voltage losses arise from delays in electrode reactions, internal resistance, and insufficient fuel or oxygen supply.
To evaluate the performance of a fuel cell, it is necessary to measure not only the open-circuit voltage but also the voltage and current under load.

Difference Between Theoretical Electromotive Force and Measured Voltage

The theoretical electromotive force of a hydrogen fuel cell can be determined from the Gibbs energy change of the reaction in which water is produced from hydrogen and oxygen.
Under standard conditions, approximately 1.23 V may be treated as the theoretical value.
However, the voltage measured in an actual fuel cell is often lower than this value even under open-circuit conditions.

Possible reasons why the measured voltage is lower include electrode-reaction overvoltage, internal resistance, purity of the fuel gas, oxygen concentration, temperature, water conditions, membrane condition, and gas leakage.
By discussing the difference between the theoretical and measured values, it is possible to understand how the fuel cell deviates from an ideal state.

Main Causes of Voltage Drop

The main causes of voltage drop in a fuel cell are activation overvoltage, resistance overvoltage, and concentration overvoltage.
Activation overvoltage is the energy loss required to drive the electrode reaction.
Resistance overvoltage is the voltage loss caused by resistance in the electrolyte membrane, electrodes, wires, contact points, and other components.
Concentration overvoltage occurs when the supply of fuel or oxygen cannot keep up with the reaction.

At low current, activation overvoltage is prominent, while resistance loss becomes larger as the current increases.
At still higher current, concentration polarization caused by insufficient fuel or oxygen supply may occur, causing the voltage to decrease rapidly.
By measuring the relationship between current and voltage, it is possible to discuss which type of loss is dominant.

Discussion of Activation Overvoltage

Activation overvoltage is the additional potential difference required to drive an electrode reaction.
Hydrogen-oxidation and oxygen-reduction reactions proceed through catalysts on electrode surfaces.
If the reaction rate is slow, the theoretical potential alone cannot produce sufficient current and an additional voltage loss occurs.

In a fuel cell, the oxygen-reduction reaction is particularly slow, so activation overvoltage tends to be large at the oxygen electrode.
The type and amount of catalyst, electrode surface area, degree of electrode wetting, and temperature affect activation overvoltage.
If the catalyst performance is insufficient, the voltage drop becomes larger.

Voltage Drop Caused by Internal Resistance

A fuel cell contains resistance in the electrolyte membrane, electrodes, current collectors, wires, contact points, and other components.
When current flows, these resistances cause a voltage drop.
This loss is called resistance overvoltage or ohmic loss.

The voltage drop caused by internal resistance becomes larger as the current increases.
If the electrolyte membrane dries and proton conductivity decreases, or if contact between the electrodes and wires is poor, the internal resistance increases.
In a region where voltage decreases approximately linearly with current, the effect of internal resistance can be considered large.

Voltage drop = I × R

Discussion of Concentration Polarization

Concentration polarization is a voltage drop that occurs when the supply of fuel or oxygen cannot keep up with the rate at which they are consumed at the electrode surface.
When a high current is drawn, hydrogen is rapidly consumed at the fuel electrode and oxygen is rapidly consumed at the oxygen electrode.
If gas supply or diffusion is insufficient, the reactant concentration at the electrode surface decreases and the voltage falls.

Concentration polarization causes a rapid voltage drop in the high-current region.
It is more likely to occur when the gas flow rate is insufficient, the electrode is blocked by water, or the diffusion layer is clogged.
If the voltage drops sharply when the load is increased in an experiment, concentration polarization should be considered.

Effect of Water Management

In a hydrogen fuel cell, water is produced as a reaction product.
The electrolyte membrane must remain appropriately moist, but too much water can block the electrodes or gas-diffusion layer and interfere with the supply of oxygen or hydrogen.
Therefore, maintaining an appropriate amount of water is important in a fuel cell.

If the membrane dries, proton conductivity decreases and the internal resistance increases.
On the other hand, if too much water accumulates, a condition called flooding occurs and gas supply is hindered.
Both cases cause a voltage drop.

Effect of Fuel Supply

In a fuel cell, sufficient hydrogen must be supplied to the fuel electrode.
If the hydrogen supply is insufficient, the oxidation reaction at the fuel electrode becomes more difficult and the voltage decreases when current is drawn.
Under high-load conditions in particular, hydrogen consumption increases, making insufficient supply more likely.

In addition, if impurities are contained in the fuel, the catalyst surface may be poisoned and the reaction rate may decrease.
In small laboratory fuel cells, gas flow rate, leakage from piping, bubbles inside tubes, fuel pressure, and other factors also affect voltage.

Effect of Oxygen Supply

At the oxygen electrode, oxygen is reduced to form water.
When air is used, the oxygen concentration is lower than in pure oxygen, so oxygen supply is more easily limited.
If the oxygen supply is insufficient, the oxygen-reduction reaction becomes more difficult and a voltage drop occurs.

Generated water tends to accumulate at the oxygen electrode and may hinder gas diffusion.
Insufficient oxygen supply is a major cause of rapid voltage drop at high current.
Comparing air supply and pure-oxygen supply makes it possible to discuss the effects of oxygen concentration and diffusion.

How to Determine Output

The output of a fuel cell is determined from the product of voltage and current.
Even if the voltage is high, the output is small when the current is small, and even if the current is large, the output does not increase if the voltage decreases greatly.
Therefore, when evaluating fuel-cell performance, it is necessary to consider output as well as voltage.

When the load resistance is changed, the relationship between current and voltage changes.
In general, there is a load condition at which the output becomes maximum.
By organizing the relationship among voltage, current, and output, it is possible to discuss under which conditions the fuel cell can generate electricity efficiently.

Output P = Voltage V × Current I

Concept of Power-Generation Efficiency

Power-generation efficiency is a value indicating how much of the chemical energy possessed by the fuel can be extracted as electrical energy.
In an experiment, it may be determined by comparing the obtained electrical energy with the energy of the consumed hydrogen.
Electrical energy is determined from the product of output and time.

Actual efficiency is lower than theoretical efficiency.
Causes include overvoltage, internal resistance, low fuel utilization, gas leakage, unreacted fuel, and energy lost as heat.
When discussing efficiency, it is easier to organize the discussion by considering voltage efficiency, fuel utilization, Faradaic efficiency, and other factors separately.

Electrical energy = Voltage V × Current I × Time t

Power-generation efficiency = Obtained electrical energy ÷ Chemical energy of fuel × 100

Discussion of Faradaic Efficiency

Faradaic efficiency is an indicator of how much of the amount of electrons theoretically obtainable from the reaction of the fuel actually flowed through the external circuit.
When 1 mol of hydrogen is oxidized, 2 mol of electrons are produced.
Therefore, the theoretical amount of electricity can be calculated from the amount of hydrogen consumed.

The actual amount of electricity that flowed is determined from the product of current and time.
If the measured quantity of electricity is smaller than the theoretical quantity, possible causes include fuel leakage without being used in the reaction, fuel crossover, side reactions, or measurement errors.
Faradaic efficiency is an indicator for evaluating how much of the fuel was utilized as electric current.

H2 → 2H+ + 2e-

Measured quantity of electricity Q = I × t

Effect of the Catalyst

In a fuel cell, catalysts are important for accelerating electrode reactions.
Hydrogen-oxidation and oxygen-reduction reactions proceed on catalyst surfaces.
Because the oxygen-reduction reaction is particularly slow, catalysts such as platinum may be used.
When the catalyst functions sufficiently, activation overvoltage becomes smaller and voltage drop can be suppressed.

If the catalyst surface becomes contaminated or poisoned by impurities in the fuel, the reaction rate decreases.
As a result, voltage and current may decrease even under the same fuel-supply conditions.
The type, amount, dispersion state, and surface area of the catalyst are strongly related to fuel-cell performance.

Effect of the Electrolyte Membrane

In a polymer electrolyte fuel cell, the electrolyte membrane has the role of allowing H+ to pass through.
Electrons cannot pass through the membrane and instead pass through the external circuit, allowing them to be used as electric current.
The higher the proton conductivity of the electrolyte membrane, the smaller the internal resistance and the more the voltage drop can be suppressed.

When the electrolyte membrane dries, H+ becomes more difficult to transport and the internal resistance increases.
On the other hand, too much water may interfere with gas supply.
The condition of the electrolyte membrane is related to both resistance loss and water management.

When the Voltage Decreases Over Time

When the voltage of a fuel cell decreases over time, possible causes include insufficient fuel or oxygen supply, accumulation of generated water, drying of the electrolyte membrane, contamination of the catalyst surface, temperature changes, and increased internal resistance.
Because the internal condition of the cell changes during power generation, the initial voltage may differ from the voltage after a certain period.

In small laboratory fuel cells in particular, even slight changes in gas supply or moisture conditions can greatly affect voltage.
If the voltage decreases slowly, drying or fuel consumption may be suspected, whereas if it decreases rapidly, insufficient supply or blockage caused by generated water may be suspected.
Observing the pattern of change over time makes it easier to discuss the cause.

Causes of Error in Fuel Cell Experiments

Causes of error in fuel cell experiments include fluctuations in fuel supply, insufficient oxygen supply, gas leakage, poor electrode contact, drying of the electrolyte membrane, accumulation of generated water, differences in catalyst condition, temperature changes, errors in load resistance, reading errors of voltmeters and ammeters, and wiring resistance.
Because reactions, mass transfer, electrical resistance, and water management are all involved simultaneously in fuel cells, multiple factors affect the results.

Causes of low voltage include overvoltage, internal resistance, concentration polarization, fuel shortage, oxygen shortage, membrane drying, and contact resistance.
Causes of low efficiency include losses of unreacted fuel, fuel leakage, heat loss, and errors in measurement time or flow rate.
Organizing the causes according to whether they affect voltage, current, or efficiency makes the discussion more specific.

When the Results Can Be Considered Good

Fuel cell experimental results can be considered good when a stable open-circuit voltage is obtained by supplying fuel and oxygen, current flows when a load is connected, and the relationships among voltage, current, and output can be theoretically explained.
In addition, if the voltage decreases as the load increases and a maximum appears in the output, this can also be discussed as behavior characteristic of a fuel cell.

Even if the measured voltage is lower than the theoretical electromotive force, the result can be considered reasonable if it can be explained by overvoltage, internal resistance, and concentration polarization.
If efficiency is calculated, it is necessary to confirm whether the calculations of fuel consumption and electrical energy are reasonable.

Example Discussions When the Experiment Did Not Go Well

When a fuel cell experiment does not go well, possible causes can be considered from results such as no voltage being produced, low voltage, almost no current flowing, unstable voltage, a rapid decrease over time, or extremely low efficiency.
Organizing the causes according to fuel supply, oxygen supply, electrolyte membrane, electrode contact, wiring, load, and measuring instruments makes the discussion easier.

How to Write Points for Improvement

In a discussion of a fuel cell experiment, writing not only the causes of error but also points for improvement makes the report easier to organize.
Points for improvement can be organized according to gas supply, electrodes and membrane, measurement conditions, and efficiency calculations.

Improvements to Fuel and Oxygen Supply

• Keep the hydrogen supply constant
• Keep the oxygen or air supply constant
• Check for gas leakage
• Securely connect the tubes
• Prevent water from accumulating in the flow channels
• Avoid insufficient reactant supply

Improvements to the Electrodes and Membrane

• Keep the electrolyte membrane in an appropriately moist state
• Ensure close contact between the electrodes and membrane
• Keep the electrode surfaces clean
• Avoid deterioration or contamination of the catalyst surface
• Properly remove generated water
• Reduce contact resistance

Improvements to Measurement and Analysis

• Distinguish between open-circuit voltage and voltage under load
• Record voltage and current simultaneously
• Set the load resistance accurately
• Record changes over time
• Measure fuel consumption accurately
• Use consistent units for electrical energy and fuel energy
• Perform multiple measurements to confirm reproducibility

Difference Between a Superficial Discussion and a Good Discussion

In a discussion of a fuel cell experiment, simply writing that “the voltage was low” or “electricity was generated” results in a superficial discussion.
A good discussion relates electrode reactions, electromotive force, overvoltage, internal resistance, concentration polarization, fuel supply, and efficiency.

Examples of Expressions That Can Be Used in Reports

The following expressions can be used when writing the results and discussion of fuel cell experiments.
Adjust the necessary parts according to your own experimental results.

• In a fuel cell, the oxidation reaction of the fuel and the reduction reaction of oxygen proceed separately.
• In a hydrogen fuel cell, H2 is oxidized at the fuel electrode and O2 is reduced at the oxygen electrode.
• Electric current is obtained because electrons flow through the external circuit.
• The measured voltage is often lower than the theoretical electromotive force.
• Causes of voltage drop include activation overvoltage, internal resistance, and concentration polarization.
• The oxygen-reduction reaction is relatively slow and tends to cause voltage loss.
• If the electrolyte membrane dries, proton conductivity decreases and internal resistance increases.
• If too much generated water accumulates, gas supply is hindered and concentration polarization increases.
• Output is determined from the product of voltage and current.
• Power-generation efficiency can be evaluated from the ratio of the obtained electrical energy to the chemical energy of the fuel.

Points to Check When Discussing Fuel Cell Experiments

Checking the following points before writing the report makes the discussion easier to write.

• Is the principle of the fuel cell explained using redox reactions?
• Are the reactions at the fuel electrode and oxygen electrode distinguished?
• Is the overall reaction of the hydrogen fuel cell written?
• Are open-circuit voltage and voltage under load distinguished?
• Is the difference between theoretical electromotive force and measured voltage explained?
• Is voltage drop organized in terms of overvoltage, internal resistance, and concentration polarization?
• Are the effects of hydrogen supply and oxygen supply considered?
• Are water management factors such as generated water and membrane drying discussed?
• Is the relationship among voltage, current, and output explained?
• Are power-generation efficiency and Faradaic efficiency considered?
• Are causes of error separated into measurement conditions and the internal condition of the fuel cell?
• Do the points for improvement correspond to the causes of error?

Summary

A fuel cell experiment is an experiment in which chemical energy is converted into electrical energy using the oxidation reaction of a fuel such as hydrogen and the reduction reaction of oxygen.
In a hydrogen fuel cell, H2 is separated into H+ and electrons at the fuel electrode, while O2, H+, and electrons react at the oxygen electrode to produce H2O.
Electricity can be generated by extracting this flow of electrons through an external circuit.

The measured voltage is often lower than the theoretical electromotive force, and the causes include activation overvoltage, internal resistance, and concentration polarization.
Insufficient fuel supply, insufficient oxygen supply, drying of the electrolyte membrane, accumulation of generated water, contact resistance, and catalyst condition also affect voltage drop.
Organizing which factors can explain the voltage drop is important in the discussion of a fuel cell experiment.

In a report, rather than simply writing that “electricity was generated” or “the voltage decreased,” organize and discuss the electrode reactions at the fuel and oxygen electrodes, theoretical electromotive force, open-circuit voltage, voltage under load, overvoltage, internal resistance, concentration polarization, water management, output, efficiency, causes of error, and points for improvement.
Fuel cell experiments are important experiments for understanding the connection among redox reactions, electrochemistry, and energy conversion.