Producing Electricity From Banana Stump: Stump Cell

This is a summer science activity that I did. This summer holiday I got a lightning idea. Actually this summer holiday I visited my native which is in Kerala, India, there are a lot of banana trees in my garden there, one day I came across a banana tree that my grandma was choping off, and suddenly I noticed a gelly substance inside it, I got curious and I came to know that it's citric acid!

At that point of time I had also came across the need of cheap energy by the people living in rural regions where there are acres of banana plantation but electricity supplies are not coming, and many rotten stumps are getting wasted, that I myself witnessed in front of me.

I got to know about this idea from Gopal Jee from Bihar, India, who discovered it, I thought to take this idea a bit far and I ended up with two crucial observations. I started learning more about the whole process to produce cheap renewable source of electricity through these banana stumps by incorporating the concept of Daniell cell here. This works on the principle of redox reactions. This can be revolutionary idea to help people living in rural regions at a affordable rate.

Supplies

1) Banana stumps (more older, more preferred)
2) Electrodes (Zinc & Copper)
3) Wires
4) Voltmeter

Understanding Redox Reactions

I started my journey by learning and studying about redox reactions. There is a famous saying which I came across "Where there is oxidation, there is always reduction — Chemistry is essentially a study of redox systems". So, before I tell you about Daniell cell, it really becomes crucial to let you know about '𝙧𝙚𝙙𝙤𝙭 𝙧𝙚𝙖𝙘𝙩𝙞𝙤𝙣𝙨'. Many chemical reactions involve transfer of electrons from one chemical substance to another, and these '𝗲𝗹𝗲𝗰𝘁𝗿𝗼𝗻 𝘁𝗿𝗮𝗻𝘀𝗳𝗲𝗿 𝗿𝗲𝗮𝗰𝘁𝗶𝗼𝗻𝘀 𝗮𝗿𝗲 𝗼𝗻𝗹𝘆 𝘁𝗲𝗿𝗺𝗲𝗱 𝗮𝘀 𝗼𝘅𝗶𝗱𝗮𝘁𝗶𝗼𝗻-𝗿𝗲𝗱𝘂𝗰𝘁𝗶𝗼𝗻 𝗿𝗲𝗮𝗰𝘁𝗶𝗼𝗻𝘀 𝗼𝗿 𝙧𝙚𝙙𝙤𝙭 𝙧𝙚𝙖𝙘𝙩𝙞𝙤𝙣𝙨. One example of such reaction is illustrated above.

Now it's necessary to understand the two important components that make up redox reactions, that are 𝗼𝘅𝗶𝗱𝗮𝘁𝗶𝗼𝗻 𝗮𝗻𝗱 𝗿𝗲𝗱𝘂𝗰𝘁𝗶𝗼𝗻. Oxidation, is nothing but 𝗹𝗼𝘀𝘀 𝗼𝗳 𝗲𝗹𝗲𝗰𝘁𝗿𝗼𝗻 whereas reduction is 𝗴𝗮𝗶𝗻 𝗼𝗳 𝗲𝗹𝗲𝗰𝘁𝗿𝗼𝗻. So basically we can understand that those reactions that involve both oxidation and reduction simultaneously are known as redox reactions. These redox reactions have wide range of applications from burning of fuel used in rockets etc. to photochromatic lenses, as well as there are also many naturally occurring redox reactions like rusting of iron, so one such application was 𝗗𝗮𝗻𝗶𝗲𝗹𝗹 𝗰𝗲𝗹𝗹. So here I incorporated the Daniell cell concept to produce electricity from banana stumps.

I learnt more about redox reactions from various sources for this project, that included Wikipedia, YouTube , various other websites and I refered to grade 11 and 12 NCERT Chemistry textbook, and simultaneously I even prepared notes. The above images illustrated are notes that I prepared, there are also various examples of redox reactions illustrated above in my notes, you can refer them to get a clear idea!

There is one last concept that I want you to wrap your heads around that is 𝗢𝘅𝗶𝗱𝗮𝘁𝗶𝗼𝗻 𝗻𝘂𝗺𝗯𝗲𝗿, for now you just remember that oxidation number is nothing but charge that we denote on the upper right side of an element. So it's done you have understood the basics and what is needed now, about redox reactions.

Understanding Daniell Cell

Daniell cell converts chemical energy produced during redox reaction to electrical energy and has an electrical potential equal to 1.1 V, when concentration of Zn²+ and Cu²+ ions is unity (1mol/dm³). The oxidation and reduction reactions occur in two different portions of the Daniell cell, the reduction half reaction occur in copper electrode, while the oxidation half reaction occur in zinc electrode. Reduction takes place at cathode and oxidation takes place at anode, there is a very popular way to remember this that is just remember "𝗥𝗲𝗱 𝗰𝗮𝘁" 𝗮𝗻𝗱 "𝗔𝗻 𝗢𝘅" , that is reduction (red) at cathode (cat) and at anode (An) oxidation (Ox) takes place.

These two compartments in the Daniell cell are known as redox couples or half cells. I have drawn in the above image illustrating Daniell cell and even wrote half cell reactions separately. A salt bridge is used to link in order to maintain overall neutrality and to complete the circuit for the flow of current. Now you have even understood about the Daniell cell, hence accomplishing step 2 of the process.

Incorporating Daniell Cell Into Banana Stumps

So I have incorporated the principle of Daniell cell into these banana stumps. First of all find a banana stump, I used the one which my grandma was discarding. Then get copper and zinc which act as electrode as Zinc readily loses electrons and copper gains it. Thus copper acts as cathode and Zinc acts as anode. Oxidation takes place at anode and reduction takes place at cathode. Now the only work we have to do is just pierce these electrodes into the banana stump, you can pierce it anywhere, it doesn't matter, now attach wires to the electrodes. There is no need of salt bridge as we are piercing it into the same banana stump. Connect electrodes wire into the voltmeter and test the flow. Finally it's done, you have a fully functional banana stump electrochemical cell with you. It's as simple as that. 3 Volts is enough to light a LED bulb for 3 hours. The stump produces electricity as long as there is citric acid inside the stump. Now you can use this electricity output to light the world around you!

1st Observation: Output Potential From Fresh Vs Old Banana Stump

I noticed that as the banana stump is getting older and older the energy output is increasing because the acid inside is increasing thereby electrolyte is increasing. Here I checked with two banana stumps, one is 2 days old and the other one is almost 1 week old. I pierced in the electrodes first into the 2 days old one and got the output voltage around 0.3 Volts and then I pierced it into 1 week old one and I got the output voltage around 0.5 Volts after two days I again checked the output of the old stump and I found a slight increase in it. This was really interesting observation, with which I concluded that as the banana stumps are getting older and older the voltage output is increasing.

𝗖𝗼𝗻𝗰𝗹𝘂𝘀𝗶𝗼𝗻: The output voltage increases with time as the stump gets older (rots) due to increase in the electrolyte present within them.

Then just for fun what I did was just took a few lemons (citric acid) and just squeezed into it, the output voltage suddenly increased and went upto 1.4 Volts in the old banana stump.

2nd Observation: Voltage Surge Reaction

I finally observed a really major thing by mistake! It was night when I was just playing with electrodes and these stumps by piercing the electrodes and checking the output again and again, that night I just pierced these electrodes into these stumps and just went to sleep, then I woke up in the morning and then had my breakfast and atlast came back to play with this, when I connected the wires into the voltmeter, the reading just shocked me! It was around 5-6 Volts!!! It was a real shock to me. Then I assumed that it may be because I pierced these electrodes into the banana stump for too long and reaction had taken place. I repeated the experiment, and got the result around 6 Volts the other day! I then concluded the result by formulating the equation, that is illustrated above in the image. With this output, I was able to light a small bulb.

𝗖𝗼𝗻𝗰𝗹𝘂𝘀𝗶𝗼𝗻 : Time till electrode pierced inside the stump is directly proportional to the voltage output.

Conclusion

According to me this idea is wonderful. I had great fun, developing this project, my summer holiday. The above graph shows the percentage of households with electricity, in some of the states of India, as you can clearly see, we have a long way to go to electrify each and every household not only in India but the whole world. This project has the potential to light up every child's life living in rural regions. In India itself there are thousands and thousands of children who live in the darkness of ignorance, and are unable to study due to darkness, even a small light bulb can light up their life.

We must all help all the needy, across the globe in any way possible, by doing good deeds however small they may be. I encourage everyone to make use of their summer holidays in a beneficial manner and indulge into making new inventions or just indulge into any interested science activity. We all having the capacity and can invent and innovate new things to make the world a better place to live.....

Thankyou!
Pranav P D