Mercury Cell is a type of Primary Cell, which is non-rechargeable in nature, meaning it can only be used once before discarding it. The Mercury Cell is generally a small button-like structure and is mainly used in low-current devices such as watches, BIOS batteries on motherboards, and pacemakers. The Mercury cell has a potential of 1.35 Volts and is made by filling chemicals like mercury, mercuric oxide, carbon powder, zinc oxide, etc., into a steel container the size of a button.
In this article, we will learn about the mercury cell and its components and working of mercury cells and different types of mercury cells, and the advantages and applications of mercury cells.
What is Mercury Cell?
The zinc anode, mercuric oxide cathode, and potassium hydroxide electrolyte make up the mercury cell, a form of dry cell. The mercury cell is a new type of cell that is used in small electrical circuits such as those hearing aids, watches, and cameras. A zinc anode and a mercury (II) oxide cathode make up this component. The electrolyte is a KOH and ZnO paste.
The cell undergoes the following reaction:
At anode:
Zn(Hg) + 2OH¯→ ZnO(s) + H2O+ 2e¯
At cathode:
HgO(s) + H2O+ 2e¯ → Hg(l) + 2OH¯
Overall cell equation is as follows:
Zn + HgO(s) → ZnO(s) + Hg(l)
It has the benefit that its potential stays basically constant during the course of its existence. The mercury cell has a voltage of about 1.35 V.
Construction of Mercury Cells
Construction of mercury cell include:
Anode zinc, cathode mercury oxide, and electrolyte (sodium or potassium hydroxide) are used in the construction of mercury cells. Given that mercury oxide is not a conductor, there may be a small quantity of graphite mixed in.
- Anode: Zinc Amalgamated with mercury
- Cathode: HgO mixed with graphite
- Electrolyte: Paste of KOH and ZnO
- Cell emf: about 1.35 V
Mercury Cell Diagram
Diagram of Mercury Cell is given as follows:
Mercury Cell Diagram
Working Principle of Mercury Cell
The mercury cell is a kind of primary cell that cannot be recharged or reused; rather, it generates current through irreversible chemical reactions in the electric cell.
The zinc compound functions as the anode in a mercury cell, where an oxidation reaction happens, while the mercury compound serves as the cathode, where a reduction reaction occurs. An electrolyte that ionizes in a molten state to conduct electricity is either potassium hydroxide or sodium hydroxide.
Electrochemical Reactions in Mercury Cell
The cathode of a mercury cell can consist of either pure mercury(II) oxide (HgO) or a combination of manganese dioxide and mercuric oxide. Some graphite are combined with magnesium oxide (MgO), which is a non-conductor of electricity.
Half-cell reaction at the cathode:
HgO(s) + H2O+ 2e¯ → Hg(l) + 2OH¯
The standard potential during the reduction reaction is +0.0977 V.
Half-cell reaction at the anode:
Zn(Hg) + 2OH¯→ ZnO(s) + H2O+ 2e¯
The overall reaction for the mercury cell:
Zn + HgO(s) → ZnO(s) + Hg(l)
Different Types of Mercury Cell
Zinc-mercuric oxide and cadmium-mercuric oxide cells are the two primary forms of mercury cells.
- Mercuric-Zinc Cell
- Mercuric-Cadmium Cell
Mercuric-Zinc Cell
- It’s a kind of mercury cell with an extended shelf life.
- The voltage (1.35 v) often keeps the cell steady.
- They have a Zn + HgO = ZnO + Hg cell reaction.
- They have electrochemical efficiencies of 250 mAH/g for mercury and 820 mAH/g for zinc.
Read More about Zinc Cloride.
Mercuric-Cadmium Cell
- It’s a temperature-stable cell that can withstand both high and low temperatures.
- The voltage is 0.91 volts. It has a 480 mAH/g (Cd) electrochemical efficiency.
- They have Cd + HgO + H2O = Cd(OH2) + Hg as their cell response.
Mercury Cell vs Dry Cell
Zinc is changed into zinc chloride in a dry cell during an electrochemical process, which makes the zinc porous. The permeable case allows a substance inside the cell to seep out, corroding the metal and shortening the cell’s lifespan. In contrast, no ions are present in the solution when the mercury cell undergoes its lifetime-altering events.
Other than that the key differences between Mercury cell and dry cell are listed in the following table:
| Mercury and zinc amalgamation |
Zinc and manganese dioxide |
| Potassium hydroxide |
Ammonium chloride or zinc chloride |
| Zinc |
Zinc |
| Mercuric oxide |
Manganese dioxide (Alkaline), Carbon (Zinc-Carbon) |
| 1.35 Volts |
1.5 Volts (Zinc-Carbon), 1.5 to 1.6 volts (Alkaline) |
| Higher |
Lower |
| Contains toxic mercury |
Less environmental impact, but still should be disposed of properly |
| Button cells for small devices |
General-purpose batteries for various applications |
| Requires proper hazardous waste disposal |
Requires proper disposal due to environmental impact |
Read More,
Applications of Mercury Cell
Some of the most common uses of Mercury Cells are:
- Mercury Cells are used in small scale devices such as small torches, watched, calculators, toys, hearing aids, etc.
- In early days, telegraph and early telephones are also used Mercury Cells.
- In military and defence, Mercury Cells are used for Triggering explosives, detonators, and signal flares.
- For railway system, operating trackside signals and switches mercury cells are used.
Advantages of Mercury Cells
Some of the key advantages of using mercury cells are:
- Extended storage life of up to ten years
- high capacity for each size
- The output voltage of 1.35V is constant.
- Mercury cells can be produced inexpensively using existing technology.
- Reducing contaminants such as oxygen, sodium chlorate, and sodium hypochlorite allows for the separation of chlorine using a mercury cell.
Health Concerns of Mercury Cells
Some of the common health concern of mercury cells are:
- Mercury’s extreme toxicity led to the phasing out of mercury cells due to environmental and health concerns.
- Using or possessing mercury cells may be regulated or prohibited in certain regions due to their hazardous nature.
Note: Despite their historical applications, mercury cells are not recommended for any modern use due to the significant risks associated with mercury exposure.
Disadvantages of Mercury Cells
Some of the key disadvantages of using mercury cells are:
- Mercury vapor inhalation damages the human body, including organs like the kidney, nervous system, digestive system, eyes, skin, and immune systems.
- The human body is extremely poisonous in even small amounts.
- It is hazardous to a child’s development during pregnancy and the first few years of life.
- Safer and more sustainable alternatives like zinc-carbon and alkaline batteries are now widely available.
Conclusion
In this article we have seen the mercury cell and its components and working of mercury cell and different types of mercury cell and advantages and applications of mercury cell. Mercury cell has many applications which we use mostly in our daily life. Mercury cell plays an important role in our daily life.
Read More,
Mercury Cell: FAQ’s
1. What is a Mercury Cell?
Mercury cell is a kind of primary cell that cannot be recharged or reused; rather, it generates current through irreversible chemical reactions in the electric cell.
2. Who Invented Mercury Cell?
The mercury cell was invented by Samuel Ruben in 1942.
3. What are two Uses of Mercury Cell?
Two primary used of mercury cells are:
- Used in Portable Electronic Devices, and
- Some specialized applications such as providing stable voltage and long shelf life, like in military and medical equipment.
4. Is Mercury Cell a Galvanic Cell?
Yes, a mercury cell is a type of galvanic cell. It generates electricity through a chemical reaction between mercury oxide and zinc.
5. Can a Mercury Cell be Reused?
Mercury cells are not rechargeable. Once the chemical reaction is complete and the battery is depleted, it cannot be reused.
6. What is the difference between a dry cell and a mercury cell?
The main difference between a dry cell and a mercury cell are:
- In Dry cell anode is Zinc and in Mercury cell anode is Zn/Hg amalgam
- In Dry cell Cathode is Graphite and in Mercury cell cathode is HgO/graphite paste
Cell reactions of Dry cell and Mercury cell :
Dry cell
- 2MnO2 + 2NH4Cl + Zn → Mn2O3 + Zn(NH3)2Cl2 + H2O
Mercury cell
7. What is Mercury Cell Battery?
A mercury battery, also known as a button cell, mercuric oxide battery, or Ruben-Mallory battery, is a primary electrochemical battery that cannot be recharged.
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