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Renewable resources of energy are needed to combat the ever-increasing emission of carbon dioxide, which is the dominant greenhouse gas responsible for global warming. Sugar based fuel cells promise an environmentally friendly alternative to fossil fuels. Here I report experimental results on the performance of a simple sugar/hydrogen peroxide fuel cell. For glucose, fructose sucrose and maltose, I measured the open circuit voltage, the short circuit current, the voltage/current relationship, and the electric power as a function of time. For glucose and fructose the fuel cells started working after a delay time of 65 min and 9 min, respectively. The maltose and sucrose fuel cells never developed significant voltages nor currents. For glucose and fructose the open circuit voltage was 0.84V. The short circuit current was for glucose 7.4mA and for fructose 6.3mA. Glucose delivered twice the maximal power (3mW) than fructose. I report on the possible chemical reactions and discuss the implications and compare them with the experimental results. My results show that a glucose/hydrogen peroxide fuel cell has the best performance and that sugar based fuel cells are promising candidates for environmentally friendly energy delivery systems.
Word Count: 188
An Investigation of the Sugar / Hydrogen Peroxide Fuel Cell
Analyses of a sugar and hydrogen peroxide
Table of Contents:
1.1 Information on the fuels used in the fuel Cell:
1.16 Hydrogen Peroxide
2.0 Materials and Method
2.11 Chemicals Required
2.12 Supplies Required
2.23 pheumatic trough
3.0 Results and Discussion
3.13 Sucrose & Maltose
3.2 Reactions at the Cathode
3.3 Reactions at the Anode?
3.3 Glucose/Hydrogen Peroxide Fuel Cell
3.32 voltage against current
3.33 exponential decay
3.35 pheumatic trough
3.4 Fructose/Hydrogen Peroxide Fuel Cell
3.42 voltage against current
3.43 exponential decay
5.1 Error minimization
5.2 Possible Errors
Carbon Dioxide from burning fossil fuels has been generally indentified as the leading cause for global warming. Renewable, carbon neutral, resources of energy can provide a solution. Many different technologies have been proposed and many challenges remain. One such technology is based on fuel cells. These are devices that make use of an electrochemical reaction in order to produce electricity from fuels. These can be gaseous, liquid, or solid. Gaseous fuel cells, like the well know hydrogen fuel cell, require sophisticated structures for the gases to diffuse. In the case of liquid fuels and liquid electron accepters much simpler fuel cell structures can be used. A schematic of a fuel cell is shown in Fig. 1.
Figure : Schematic of a liquid based fuel cell. The current I flows from the cathode to the anode; the cell generates a voltage V across the external circuit; positive ions flow through the ion permeable membrane. The fuel cell produces a electrical power
W = IÂ·V.
Typical fuel cells require proton exchange membranes that separate the anode and cathode compartments from each other. This prevents the direct reaction of the fuels at the platinum electrodes. 2 Simpler designs with glass filters are possible for some fuel cells such as the one used here.
Some liquid fuel cells can be powered by sugar as a fuel. Sugar has the advantage that it is produced in large amounts from sugar cane, sugar beet, corn, and fruits, and is thus fully renewable. One technology uses sugar and hydrogen peroxide, while others make use of bacteria or enzymes.
In this investigation I consider a fuel cell that makes use of different sugars solved in potassium hydroxide as fuel and hydrogen peroxide solved in potassium hydroxide as an electron acceptor. The principle of the design is similar to the one proposed by Blume and is described in detail later. I investigated the sugars maltose, glucose, sucrose, and fructose. For each sugar I measured the open circuit voltage, the short circuit current, the voltage/current relationship, and the electric power as a function of time.
In order to answer the question, how different sugars effect the performance of a sugar/hydrogen peroxide fuel cell, I set myself the following main objectives:
Design an experimental setup that allows the quantitative investigation using a digital data acquisition system.
Describe the different chemical reactions.
Measure the open circuit voltage and the short circuit current.
Determine the current/voltage characteristics (I-V curve).
Measure the power as a function of current and voltage.
Identify limiting factors and improvements.
1.1 Information on the fuels used in the Fuel Cell:
Before I start with the experiment, I would like to examine the substances used and to maybe see, which substances should have a good energy output. Sugars are carbohydrates, which are organic molecules consisting of hydrogen, carbon and oxygen. They are produced by plants through photosynthesis. Sugars constitute a main ingredient in the metabolism of plants and mammals. They can be classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides. A monosaccarharid is a simple sugar, composed of hydroxyl groups. Monosaccharid molecules are either called triose, tetrose, pentose, or hexose, depending on how many carbon atoms they have (hexose means 6 atoms, pentose 5, tetrose 4, etc.). Disaccharides are two monosaccharides covalently linked together. Oligosaccharides are chains of more than two monosaccharides. Long chains of covalently linked monosaccharides or disaccharides are called polysaccharides. In this investigation I considered only mono- and disaccharides as simple sugars are more reactive.
Monosaccharides can be divided into two groups aldoses like glucose, which have a aldehyde functional group at one end and ketoses like fructose which have a ketone group (at one end). Monosaccharides have a stereoisomerism. For example, as shown in Fig. 2., glucose has two stereo isomers. The isomerism refers to the chiral carbon farthest from the aldehyde group. The two stereo isomers are designated D-Glucose or L-Glucose. D is the most naturally occurring isomer.
Figure : The isomers of glucose.
Monosacharides that are either pentoses and hexoses can cylize. Here the ketone or aldehyde funcitonal group reacts with the hydroxil group of the chiral carbon (or anomeric carbon) farthest from the ketone or aldehyde functional group. Cylization usually occures when the monosaccharides is in an aqueous solution. The cyclization of D-Glucose is shown below:
Figure : ...
1.12 Glucose (C6H12O6):
Glucose is a monosaccharide carbohydrate. As mentioned before Glucose has two isomers D- and L-Glucose. The molecular structure can be seen above.
Glucose can be obtained by hydrolysis of vegetable starches of any kind, such as maltose, sucrose, lactose, glycogen and cellulose. But it is usually manufactured from cornstarch.
1.13 Fructose (C6H12O6):
Like Glucose, Fructose is also a monosaccharide carbohydrate. Like Glucose it has two isomers D and L. The molecular structure and the cyclization of Fructose is shown below.
Fructose is produce by way of a process that converts about half of the glucose in corn syrup into fructose. The process uses an isomerase enzyme.
1.14 Sucrose (C12H22O11 ):
Sucrose is most commonly known as sugar. It is a disaccharide carbohydrate Composed of the two monosaccharides Î±-D-Glucose and Î²-D-Fructose. It can be extracted from either beets or sugar cane. About 70% off all sucrose is extracted from sugar cane, the other 30% are extracted from sugar beet.
1.15 Maltose (C12H22O11):
Maltose is a disaccharide carbohydrate produced through either hydrolysis of a polysaccharide like starch or use the enzyme diastase on starch or any polysaccharide.
1.16 Hydrogen Peroxide (H2O2):
Hydrogen Peroxide (33%) is clear colorless liquid which is a strong oxidizer, that with contact with other materials may cause fire and causes burns to the eyes, skin, and respiratory tract. If the Hydrogen Peroxide is uncontaminated it normally decomposes slowly to release oxygen. It should be kept in the dark and in a closed but vented container. This prevents evaporation and contamination. The solution should be kept cold it as if it is heated is decomposes violently and fast. The is recommended to rotate the stock to keep the concentration.
The Fuel Cell:
The schematic of the fuel cell above shows the which substances are were in the fuel cell. The design follows the suggestions by Blumes.
On the left side, at the anode, the sugar (either Glucose, Fructose, Sucrose, or Maltose) is added with a potassium hydroxide solution. On the right, at the cathode, are the substances hydrogen peroxide and potassium hydroxide are used.
Now I will the possible reactions that can happen at the cathode and the anode.
Reactions at the Anode:
At the anode (left side) the substances potassium hydroxide and a sugar (Glucose, Fructose, Sucrose, or Maltose) is present. But before we go into detail with each separate chemical formula. I would like to explain the reactions in general terms. Any sugar that forms an aldehyde or a ketone in an alkaline solution, is called a reducing sugar. A reducing sugar is basically a sugar that act as a reducing agent. A sugar can only be oxidized if it can readily switch between the linear form (open-chain form) and ring form. The linear form allows the aldehyde or ketone functional groups to become "free". These groups then readily oxidize. In order for the sugars to have a linear form, the anomeric carbon has to be "free", meaning that the bond between the anomeric carbon and the oxygen can be opened. Glucose and Fructose can are reducing sugars since they can readily switch between there linear and ring form.
The oxidation of Glucose: Below is the chemical formula for the oxidation of glucose, the formula is shortened with R, as only the aldehyde group is important for this reaction. This formula is greatly simplified, there are many complex oxidations and rearrangements of the decomposition products of Glucose.
ox: R-CHO (aq) + 3OH Ì… (aq) â†’ R-COO Ì… (aq) + 2H2O + 2e Ì…
The oxidation of Fructose: One would think that fructose is not a reducing sugar, due to the reactivity of the ketone fructional group, but in fact Fructose can isomerise into an aldose Since the aldehyde group reacts the chemical formula is exactly the same as with glucose.
ox: R-CHO (aq) + 3OH Ì… (aq) â†’ R-COO Ì… (aq) + 2H2O + 2e Ì…
Not all diassachrairdes can readily undergo oxidation. Sucrose is not a reducing sugar because it does not have a linear form, because the anomeric carbon is not free. Maltose, on the other hand, is a reducing sugar because one of the anomeric carbons of the two Glucose molecules it is composed of, is free, allowing one of the Glucose molecules to open.
The oxidation of Maltose: Since this reaction also only involves the aldhyde group it is the same as the oxidations of Glucose and Fructose.
ox: R-CHO (aq) + 3OH Ì… (aq) â†’ R-COO Ì… (aq) + 2H2O + 2e Ì…
Reactions at the cathode:
At the cathode (right side) the substances hydrogen peroxide and potassium hydroxide are present. A large variety of reactions could be taking place at the cathode:
First a hydrogen peroxide decomposes in to water and oxygen gas general. This reaction is not dependent on electrical power of potassium hydroxide. It only needs enough energy in order to react.:
2 H2O2 (aq) â†’ 2H2O (l) + O2 (g)
The oxygen produced from the decomposition of hydrogen peroxide then can react with the water present and electrons provided by the oxidation of the sugars at the anode:
O2 + 2H2O + 4e Ì… â†’ 4OH Ì… (aq)
The hydroxide molecules provided potassium hydroxide reacts with the hydrogen peroxide:
H2O2 (aq) + OH Ì… (aq) â†’ HO2 Ì… (aq) + H2O
The reaction above can be seen as an intermediate step as the products react further. The HO2 Ì… can undergo two different energies, one of them producing electrical energy and the other requiring it:
First the reaction that produces electrical energy:
HO2 Ì… (aq) + OH Ì… (aq) â†’ O2 + H2O + 2e Ì…
Now the reaction the requires electrical energy most likely derived from the oxidation of Glucose.
HO2 Ì… (aq) + H2O + 2e Ì… â†’ 3OH Ì… (aq)
Function of the platinum electrodes:
The platinum electrodes also have an effect on reactions that take place in the Fuel Cell. According to the paper "Energy density of a methanol/hydrogen peroxide fuel cell" which describes the use of platinum as a catalyst in a methanol/hydrogen peroxide fuel cell, it states that platinum catalyses reaction 1 more favorably, decomposition reaction of hydrogen peroxide. This causes a little usable electrical current. On the other hand the paper states that a large number of hydrogen peroxide molecules undergo reaction 5 and that leads to a usable current, stable current.
Evaluation of the possible reactions:
The majority of the reactions that will happen at the cathode will most likely be the decomposition of hydrogen peroxide (reaction (1)). But the following reaction (2) with oxygen will most likely not happen that often due to the fact that the gaseous oxygen will escape the solution very fast. Reaction (3) and the following reaction (5) are of great importance due to the fact that reaction (3) produces the reactants needed for reaction (5), and that reaction (5) requires 2 electrons the exact amount of electrons that is produced at the anode.
Above is a visualization of the reactions taking place in the Fuel Cell. Reaction (2) was left out because most of the oxygen will most likely escape the fuel cell before reacting.
I hypothesize that the sugars Glucose, Fructose, and Maltose will produce electrical power, and the sugar Sucrose will not.
2.0 Materials and Method:
2.11 Chemicals Used:
-Hydrogen peroxide concentration 33% produced by VWR, BHD Prolabo
-Hydrochloric Acid concentration 33%
-Potassium Hydroxide concentration 25%
-D-Glucose produced by AppliChem GmbH in 2004
-D-Fructose produced by Merck KGaA in 2000
-Sucrose produced by Merck KGaA in 1990
-Maltose produced by Merck KGaA in 1981
2.12 Supplies Needed:
-U-tube with glass filter provided by
-2 electrolytically plated platinum electrodes provided by the FKG
-variable resistor from 1-100 ohm provided by the Max-Plank Institute for Self-Organization and Dynamics produced by
-digital data acquisition system provided by....produced by
- senors used.....
-4 25ml graduated cylinders provided by....produced by
-1 100ml graduated cylinder provided by....produced by
The chemicals: glucose, fructose, sucrose, maltose, and hydrogen peroxide where provided by the school (Felix Klein Gymnasium) and used as received. The chemicals, hydrochloric acid potassium hydroxide was provided by the school but in its solid state so the base had to be produced with de-ionized water.
Before anything can be done, the U-tube has to be cleaned with nitrohydrochloric acid(1 part concentrated nitric acid and 3 parts concentrated hydrochloric acid) because the glass filter possibly has some heavy metals that could react with the hydrogen peroxide, and they should be removed.
The original method was provided by the source (Prof. Blume) but I changed the and adapted the procedure to fit my experiments.
Schematic of Experiment:
Setting up the Fuel Cell:
The Fuel Cell should be set up according to the schematic above. The U-Tube with the electrodes attached, as shown in the schematic, will as the Fuel Cell. Depending on the which value is being measured the setup of the experiment will be slightly different. The basic setup of the fuel cell will stay the same.
The solution containing 10 ml of hydrogen peroxide (w=33%) and 40 ml potassium hydroxide (w=25%) needs to be cold when the experiment starts because it decomposes at room temperature. These solutions should be kept in a refrigerator.
The other solution containing 5 g of sugar and 40 g of potassium hydroxide, should be immediately mixed before the experiment takes place because once mixed, the sugar starts reacting with the potassium hydroxide.
Once both solutions are prepared 25 ml of each solution and put one it in its corresponding side of the U-tube. The hydrogen peroxide solution goes at the cathode and the sugar solution goes to the anode.
Schematic for Voltage Measurement:
Here one can see the circuit setup for the measurement of the voltage.
Schematic for Current/Voltage Measurement with a decade Resistor:
This schematic is very similar to the schematic for voltage measurement it just adds one more circuit for the resistance and current measurement.
Once the fuel cell is running with its maximum voltage, the resistance is then changed every 10 seconds and the voltage and current magnitude is measured.
For no matter which sugar was used, there were many bubbles produced at the cathode. Over time the bubble production decreases.
When the solution of anode compartment for Fructose is mixed, it turn yellow.
For Fructose, and Glucose, the solution at the anode becomes yellow, the solution of the Fructose has a darker yellow than the Glucose.
Very few bubbles are produced at the anode
The Maltose Fuel Cell only produces are voltage of 0.036V and the Sucrose Fuel Cell only 0.02V
It takes time before the Fuel Cells of Fructose and Glucose produce a high voltage.
When the electrodes are shaken the electrical energy increases greatly.
Here you can clearly see that the voltage is negative and then suddenly increases at around 1,500 seconds or about 25 minutes after the start of the experiment.
Here you can clearly see that the voltage is negative and then suddenly increases at around 270 seconds.
Changing the resistance of the Glucose Fuel Cell from 100 to 0 and its effects on the current and voltage:
Changing the resistance of the Glucose Fuel Cell from infinity to 0 and its effects on the current and voltage: note at 660 seconds I did a mistake of setting the things:
Current in Relation to the power of the Glucose Fuel Cell:
Voltage in Relation to the power of the Glucose Fuel Cell:
Current in Relation to the power of the Fructose Fuel Cell:
Voltage in Relation to the power of the Fructose Fuel Cell:
As one can see in fig. (#) the voltage against current, with a variable resistance, have striking similarities, especially at the voltage of 0.4 V and below both lines follow the same curve. It appears that glucose has a higher current at low voltages. They might have been the same if is the lengths and between the different resistances where the same.
Above there is a visualization of the voltages produced by the different sugars in the fuel cell. Glucose and Fructose have a minimal difference in voltage but the sugars Maltose and Sucrose clearly are not to be used in this fuel cell as the voltage they produce is almost nothing.
Above is a bar graph of the currents produced at a resistance of 0 from glucose and fructose. It is clearly seen that glucose produces 0.0011 amps more than fructose.
3.32 plotting voltage against current
3.33 exponential decay Fig (#
The above graph show a voltage of
3.4 Fructose/Hydrogen Peroxide Fuel Cell:
3.42 U/V fig.
3.43 diffusion fig.
3.5 Discussion of Data: Fig.(#)
Analysis and Evaluation:
My hypothesizes about the energy production of Glucose, and Fructose, is true. But Maltose did not produce a high voltage. This is strange as Maltose is a reducing sugar. It is possible that the Maltose was contaminated in some way, as it is 28 years old.
What is very interesting is that both Fructose and Glucose had a "negative" voltage before they increase. The term "negative" voltage means that the voltage was actually higher at the cathode then at the anode. The only explanation for this is that the hydrogen peroxide is reacting and producing electricity as shown with reaction 4. The reason why it takes 65 minutes for Glucose and Fructose only 8 minutes and 45 seconds to produce a high voltage, might be that the Fructose solution for the anode compartment already turned yellow before the experiment even started. This shows that the fructose already started reacting and decomposing, probably making more reactive than the Glucose. It is stated by the Blume Website the yellow color comes from the many complex oxidations and rearrangements of the decomposition products of the sugars. Perhaps the It is very interesting voltages suddenly increase. The voltage of the Glucose FC increases almost like an asymptote. It is as if a switch was just thrown. Fructose gradually increases in comparison to Glucose.
It was observed that there where many bubbles at the cathode electrode, this shows that a great deal of the Hydrogen Peroxide reacts to produce oxygen. Some of the oxygen was most likely reduced.
The observation that the voltage increases when the electrodes are shacked shows that the Fuel Cell needs a propeller of some kind in order to move the solution in the Fuel Cell. This will allowing more reactants to collide with each other.
In order to compare the energy production of the Fuel Cells, one needs to compare, electrical current density
I have demonstrated that electrical power produced from a fuel cell using hydrogen peroxide as an oxidizing agent and the sugar, Glucose or Fructose, as a reducing agent. Both sugars produce almost the same amount of energy but one of the sugars seems to be more reliable than the other. For all three trials, Fructose consistently starts producing power just under 10 minutes after the fuel cell was "activated". Unfortunately the time it takes for Glucose tostart producing very irregular, sometimes 25 minutes after "activation" or 102 minutes after "activation".
As described above the sugar/hydrogen peroxide fuel cell would produce a greater voltage and electrical power if the Fuel cell had a propeller in order to mix the reactants
5.1 Error minimization
I did everything in my power to keep errors to a minimum. Some of the things that I did where:
-cleaning the contacts of the cables with sandpaper which had corroded over time.
-I used all of the same lab equipment so that the experimental results would not change from different experiments because of the used of different lab equipment.
5.2 Possible errors:
Some of the chemicals where very old and kept in very old containers. The oldest container was at least 28 years old and held maltose(reference) and containers have notice on them that the containers become poruse after 5 years because the light and should be replaced. This was not done. Measurement error might have lead to slight differences in the experiments. For example, the concentrations of the substances might have been slightly different. Slight temperature differences between the different experiments, might have also lead to some differences in the rate of the reaction ( the experiments where done on different days). Since the experiments were done at different times on different days the cables might have corroded causing a slight difference in the conductivity of the cables. Of course the errors caused by the equipment are constant and do not affect the experiments.