Umair Gaines
Electrochemistry is a branch of physical chemistry that deals with the study of the relationship between electrical energy and chemical changes. It involves the movement of electrons via an electronically conducting phase, such as an external electrical circuit, between electrodes separated by an ionically conducting and electronically insulating electrolyte. An electrochemical cell is a device that generates electrical energy from chemical reactions, and it can also cause chemical reactions to occur when an electric current is passed through it. These electrochemical cells can be further classified into galvanic and electrolytic cells. While galvanic cells generate electrical energy from spontaneous redox reactions, electrolytic cells use electric currents to drive chemical reactions, such as the decomposition of water into hydrogen and oxygen.
| Characteristics | Values |
|---|---|
| Definition | The branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change. |
| Types of Electrochemical Cells | Galvanic or Voltaic cells, Electrolytic cells |
| Electrolytic Cells | A class of electrochemical cells that use electric currents to facilitate the cell reaction. |
| Galvanic Cells | Electrochemical cells that generate electrical energy from spontaneous redox reactions. |
| Electrolytes | Usually a solution of water or other solvents in which ions are dissolved. |
| Electrodes | A cathode and an anode which are electrical terminals consisting of a suitable substance at which oxidation or reduction can take place. |
| Electrons | Move from the anode to the cathode. |
| Primary Cells | Single-use batteries that make up about 90% of the battery market. |
| Secondary Cells | Rechargeable batteries that have been gaining market share. |
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Electrochemical cells
Types of Electrochemical Cells
There are two main types of electrochemical cells: voltaic (galvanic) cells and electrolytic cells.
Voltaic (Galvanic) Cells
Voltaic cells, also known as galvanic cells, produce electrical energy from chemical energy. They are named after Luigi Galvani and Alessandro Volta. These cells are made up of two half-cells, one that undergoes oxidation and the other reduction. A wire connects two different metals (e.g. zinc and copper). When a spontaneous redox reaction occurs, energy is released, and this energy can be used to perform tasks.
Electrolytic Cells
Electrolytic cells are a type of electrochemical cell that produces chemical reactions. They are often used to decompose chemical compounds in a process called electrolysis. These cells have a cathode and an anode, which are electrical terminals where oxidation or reduction can take place.
Batteries and Fuel Cells
When one or more electrochemical cells are connected in parallel or series, they form a battery. Primary cells are single-use batteries, while secondary cells are rechargeable. Fuel cells, on the other hand, are a type of electrochemical cell that converts chemical energy to electricity by reacting hydrogen fuel with oxygen or another oxidizing agent. Unlike batteries, fuel cells require a continuous source of fuel and oxygen to sustain the reaction.
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Electrolytic cells
Electrochemical cells that generate an electric current are called galvanic or voltaic cells, and those that generate chemical reactions, via electrolysis for example, are called electrolytic cells. An electrolytic cell is an electrochemical cell in which applied electrical energy drives a non-spontaneous redox reaction.
An electrolytic cell is a device that converts electrical energy to chemical energy, or vice versa. It typically consists of two metallic or electronic conductors (electrodes) that are separated and in contact with an electrolyte. The electrodes are connected to a source of direct electric current, which causes one of them to become negatively charged and the other positively charged. Positive ions in the electrolyte migrate to the negative electrode (cathode) and there combine with one or more electrons, losing part or all of their charge and becoming new ions with a lower charge or neutral atoms or molecules. At the same time, negative ions migrate to the positive electrode (anode) and transfer one or more electrons, also becoming new ions or neutral particles. The overall effect of the two processes is the transfer of electrons from the negative ions to the positive ions, a chemical reaction.
The direction of electron flow in electrolytic cells may be reversed from the direction of spontaneous electron flow in galvanic cells, but the definition of both cathode and anode remain the same, where reduction takes place at the cathode and oxidation occurs at the anode. Both electrolytic and galvanic cells require a salt bridge, have a cathode and anode side, and have a consistent flow of electrons from the anode to the cathode.
An example of electrolysis in an electrolytic cell is the decomposition of water into hydrogen and oxygen, and of bauxite into aluminium and other chemicals. Electroplating (e.g. of Copper, Silver, Nickel or Chromium) is also done using an electrolytic cell.
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Batteries
A battery consists of two electrical terminals, the cathode and the anode, separated by a chemical material called an electrolyte. The cathode and anode are made of different types of metals or other chemical compounds. The cathode is the site where reduction occurs and is generally represented by a positive (+) sign. The electrons flow from the anode to the cathode, increasing the chemical potential energy and charging the battery.
In a rechargeable battery, the process can be reversed, and electrons and ions can move in either direction through the circuit and electrolyte. When the battery is being charged, the electrons move from the cathode to the anode, converting the chemical potential energy to electricity in the circuit and discharging the battery. During this process, the oppositely charged ions move inside the battery through the electrolyte to balance the charge of the electrons moving through the external circuit.
The chemical reactions that occur in rechargeable batteries are not perfectly reversible, and with each charge cycle, the electrodes degrade a little more, causing a loss of performance over time. Scientists are still studying the complex chemical processes in batteries to develop a new generation of highly efficient electrical energy storage.
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Corrosion
Electrochemistry is a branch of physical chemistry that deals with the relationship between electrical potential differences and identifiable chemical changes. These reactions involve the movement of electrons via an electronically conducting phase, such as an external electrical circuit, between electrodes. When a chemical reaction is driven by an electrical potential difference, it is called an electrochemical reaction.
The process of corrosion involves the oxidation of metals, with those higher in the reactivity series, such as iron and zinc, being more susceptible. The presence of moisture, especially saltwater, and impurities like salt, can increase the rate of corrosion. Corrosion can also occur inside crevices of aluminium alloys and stainless steels due to the formation of a differential aeration cell.
The economic impact of corrosion is significant, with the cost of corrosion management and losses to the economy amounting to billions of dollars annually. Understanding the electrochemistry of corrosion is crucial for its prevention, and techniques such as fusion-bonded epoxy (FBE) and epoxy-coated rebar coatings have been developed to mitigate corrosion in pipelines and reinforcing steel industries.
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Electrolysis
The process is carried out in an electrolytic cell, which consists of positive and negative electrodes dipped into a solution containing positively and negatively charged ions. The substance to be transformed may form the electrode, constitute the solution, or be dissolved in the solution. The electric current (i.e. electrons) enters through the negatively charged electrode (the cathode), and the components of the solution combine with the electrons and are transformed (reduced). The products can be neutral elements or new molecules. The components of the solution also travel to the other electrode (the anode), where they give up their electrons and are transformed (oxidised) into neutral elements or new molecules.
The main components required to achieve electrolysis are an electrolyte, electrodes, and an external power source. Electrolytes are chemical substances that contain free ions and carry electric currents. Ions in electrolytes must be mobile, or else electrolysis cannot occur. A liquid electrolyte can be produced through solvation or the reaction of an ionic compound with a solvent (such as water) to produce mobile ions. The electrodes are separated by a distance that allows a current to flow between them through the electrolyte and are connected to the power source.
The electrochemical reduction or electrocatalytic conversion of CO2 can produce valuable chemicals such as methane, ethylene, and ethanol. The electrolysis of carbon dioxide gives formate or carbon monoxide, and sometimes more elaborate organic compounds such as ethylene. This technology is being researched as a carbon-neutral route to organic compounds.
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Frequently asked questions
An electrical chemical system, also known as an electrochemical cell, is a device that generates electrical energy from chemical reactions.
Examples of electrochemical cells include galvanic cells, electrolytic cells, and fuel cells.
Electrochemical cells consist of two half-cells, each with an electrode dipped in an electrolyte. One half-cell loses electrons (oxidation) while the other half-cell gains electrons (reduction). This creates a difference in charge, allowing the flow of electrons, which is an electric current.
A galvanic cell, or voltaic cell, converts chemical energy into electrical energy through spontaneous redox reactions. Electrolytic cells, on the other hand, use electric currents to drive non-spontaneous redox reactions and convert electrical energy into chemical energy.
Electrochemical cells have various applications, including batteries, electroplating, and the production of hydrogen and oxygen through electrolysis. They are also used in spacecraft and grid energy storage systems.
