Cathodes and anodes are two types of electrodes within an electrical cell denoting the point where electricity both moves into the cell and where it leaves from.
Key Takeaways
- Cathodes are electrodes where reduction occurs, gaining electrons; anodes are electrodes where oxidation happens, losing electrons.
- In electrochemical cells, cathodes attract positively charged ions (cations); anodes attract negatively charged ions (anions).
- In batteries, the cathode is the positive terminal, and the anode is the negative terminal; in electrolysis, the anode is positive, and the cathode is negative.
Cathode vs Anode
The difference between an anode and a cathode is that electrons will move away from the anode, whereas they move into the cell’s cathode.
Want to save this article for later? Click the heart in the bottom right corner to save to your own articles box!
The cathode and anode locations are not fixed within a cell and can change depending on what happens at any given time. For example, when recharging a rechargeable battery.
Anodes and cathodes in the context of a battery can be confusing, as the labelling of the positive and negative sides of the storm often does not match their respective charges.
Comparison Table
| Parameter of Comparison | Cathode | Anode |
|---|---|---|
| Electron movement | Flows into the cathode | Cruises out of the anode |
| Net charge | Negative (electrolytic cells), positive (galvanic cells) | Positive (electrolytic cells), negative (galvanic cells) |
| Attracts | Cations | Anions |
| Reaction taking place | Reduction | Oxidation |
| What happens in charging | Creation of electrons | Consumption of electrons |
What is Cathode?
A cathode refers to an electrode inside an electrical cell (either galvanic or electrolytic) with negatively charged electrons entering it.
The cathode is almost always referred to as the positive electrode, despite having a net negative charge.
This is because there has been a positive increase in the number of electrons at that side, hence why the cathode side will always be marked positive on a battery, rechargeable or not.
This increase in the number of electrons is known as a reduction reaction, as this refers to a reduction in the element’s oxidation state.
For example, in a zinc-manganese dioxide battery, the most common chemical construct of a household battery, we see the electrons move from the negatively charged zinc molecules to the positively charged manganese.
This means that the manganese dioxide side of the battery is our cathode and that as the battery “charge” is used up, the zinc ions become positively charged cations attracted to the cathode end of the battery and migrate across.
It is important to note that in some instances, for example, when charging a battery, the anode and cathode change ends.
The electrons at the positive end of the cell are consumed, meaning there is a decrease in the number of electrons as they move away, which means this end is now the anode.
What is Anode?
An anode is an electrode inside an electrical cell from which electrons depart and head towards other molecules in different parts of an electrical cell or external to the cell.
For example, in a household battery, the anode is almost always called the negative side of the cell, despite having a positive charge from the electrons moving away.
This decrease in the number of electrons is known as an oxidation reaction and gives the molecules on the anode side of the cell a positive charge, turning them into cations.
In our battery example, the zinc side is the anode, as electrons move from the zinc to the manganese dioxide.
Once the manganese dioxide molecules have received their electrons from the zinc molecules, their negative charge will draw them across to this side of the battery as anions.
When charging a battery, just as with the cathode, the location of the anode will be swapped around.
During charging, the anode material will be oxidized, and electrons will be created while at the same time being removed from the other end of the battery.
This means that electrons are now moving into the electrical cell via the negative side of the cell, indicating that this site is now the cathode whilst the battery is being charged.
This redistributes the electrons to their positions before (although not quite to the same extent) and allows the battery to provide a charge once again.
Main Differences Between Cathode and Anode
- Electrons will flow into an electrical cell or system through the cathode electrode and leave from the anode electrode. These will change location under certain circumstances, i.e. battery recharging.
- The cathode will have a net negative charge in electrolytic cells, such as a disposable battery, and positive control in galvanic cells, such as a recharged battery. Anode electrodes will undergo the opposite.
- Once the movement of electrons has begun in the electrical cell (discharging), the resulting anions will be attracted to the anode end of the cell. In contrast, the cations will be attracted to the cathode end.
- The process of electrons flowing into the cathode is known as reduction, resulting in a negative charge and a reduction of the molecule’s oxidation number. Whereas with the anode, we will see a positive direction from the electrons leaving; the process is known as oxidation.
- During charging, at the cathode end, we will see the creation of electrons through the oxidation of the anode material. In contrast, we will see uptake and reduction of the electrons at the anode end.
I’ve put so much effort writing this blog post to provide value to you. It’ll be very helpful for me, if you consider sharing it on social media or with your friends/family. SHARING IS ♥️
Piyush Yadav has spent the past 25 years working as a physicist in the local community. He is a physicist passionate about making science more accessible to our readers. He holds a BSc in Natural Sciences and Post Graduate Diploma in Environmental Science. You can read more about him on his bio page.
