Study electrolysis of water

Objective 

To study the electrolysis of water 

 

Theory 

Electrolysis and composition of water 

Electrolysis is the chemical process of using electric current to decompose a substance into an electrolyte.  An electrolyte is a substance, usually an iconic compound, that conducts electricity. Water, a molecular compound comprising oxygen and hydrogen in a 2:1 ratio, is represented by the chemical formula HO. 

What is the electrolysis of water? 

  • Water electrolysis is the scientific procedure of separating water into its component gases of hydrogen and oxygen. The reaction is facilitated by using a specialised device called an electrolyzer.  
  • Hydrogen production using this method is widely acknowledged for its effectiveness as a sustainable and environmentally friendly fuel alternative.  
  • Its utility extends to diverse sectors, such as power generation and the food industry.  

Principle

The DC produced by an electrolyte consisting of hydrogen and oxygen is directly proportional to the electrical charge in the solution. The cathode contains hydrogen electrolytes, while the anode has oxygen electrolytes. 

Process 

When an electrical power source is connected to metal plates made of platinum or iridium and an electrical current is passed through the solution, the ionic compounds are broken down into simpler substances. Hydrogen is generated at the cathode side, while oxygen is produced at the anode side. The chemical reaction of gas decomposition occurs by transferring electric current through the solution.                                                                                                                                                                           Fig.1 Process of electrolysis of water 

Both oxygen and hydrogen gas produced air bubbles at the places of the anode and cathode, where the anode observes the positive ions (oxygen), and the cathode observes the negative ions (hydrogen).  

Capturing gases released from the electrodes 

  • Using the chemical test called bubble test to trap the generated gas bubbles from both the electrodes of the anode and cathode. The gas bubbles were trapped in two test tubes that were filled with water.  

Electrolysis of water by the addition of salts 

  • Salts undergo complete dissociation into anions and cations when dissolved in water. Additionally, it enhances the levels of concentration and conductivity. 
  • The common salt dissociates into sodium (Na+) and chloride (Cl-) ions. These ions carry electric charge and allow current to flow more easily through the solution. It may be drawn to the electrodes along with hydrogen and oxygen.  
  • Due to having a lesser standard electrode potentiality of water, salt is highly recommended for water electrolysis.

Equations of electrolysis of water (neutral pH) 

  • The chemical reaction occurs in the cathode: 2H2O(l) + 2e– → H2(g) + 2OH                            
  • The chemical reaction occurs in the anode: 2H2O → O2(g) + 4H+ + 4e–                                      
  • The net reaction of electrolysis of water is: 2H2O + Electrical energy → O2 + 2H2                    

The connection between water electrolysis and Faraday’s First Law of electrolysis 

The electrolysis process of water relates to the first law of electrolysis coined by Michael Faraday. The law states that the amount of reaction at any electrode during electrolysis by a current is directly proportional to the quantity of electric current passed through the electrolyte. 

                                                                                                                   m 𝛂 Q 

Here, m represents the mass of the electrolyte. 

Q represents the charge of the electrolyte. 

Role of electrocatalysts  

Electrocatalysts are non-consumable compounds that enhance the electrochemical processes. The water electrolysis cell’s operating circumstances dictate the design of the catalysts. 

For example, the inert platinum electrode can be enhanced as a catalyst through: 

  • Increasing the surface area with nanoparticles.  
  • Changing the electronic states with other catalytic substances. 

Role of an electrolytic cell (Electrolyzers) 

                                                                                                                Fig.2 Structure of an electrolytic cell 

An electrolytic cell is a device which is mainly used in the process of electrolysis. It has positive and negative charges that help to store positive and negative electrolytes in the cathode and anode during the process. 

Three types of electrolyzers are being used, depending on the transport of electrolytes. 

Name  Uses 
Polymer Electrolyte Membrane (PEM) electrolyzer  Separates polymer electrodes, facilitating hydrogen ion formation during oxidation, subsequently passing hydrogen to the cathode as a gaseous material. 
Alkaline electrolysers  A dilute aqueous solution of sodium (or potassium) hydroxide is used to transport hydroxide ions to the anode, forming oxygen. 
Solid oxide electrolyzer  It employs ceramic oxide to segregate electrodes, wherein water undergoes reduction into hydrogen and oxide ions at the cathode, and the generated oxide ions are transported to the anode, ultimately stored as gaseous oxygen. 

 

Factors affecting the efficiency of electrolysis 

  • The result of electrolysis relies on the type of material and product. 
  • The number of electrons transferred depends on the total ions in the solution. 
  • Electron transfer relies on how quickly they move to the electrodes. 
  • Efficiency in electrolysis depends on the energy electrons need to move to the electrodes. 

Applications of electrolysis of water 

  • It is used in space stations to generate oxygen gas. 
  • It is utilised in the process of manufacturing hard water. 
  • The hydrogen gas is produced through the electrolysis of alkali (base) products for small-scale purposes in chemical industries.  
  • The hydrogen gas is generated through electrolysis and mixed with oxygen to produce the oxyhydrogen used in welding and other applications. 

Difference between Electrolytes and nonelectrolytes  

Property  Electrolytes  Nonelectrolytes 
Conductivity  

Electrolytes are chemical substances that may dissolve in water and generate ions, facilitating electricity transmission through the solution.

Nonelectrolytes are chemical substances that do not conduct electricity when dissolved in water. 

Ionization 

Electrolytes may be ionized when dissolved in water. Thus, electricity is transmitted through the solution.

Nonelectrolytes may not be ionised when dissolved in water. 

                                                                                                                           

Learning Outcomes 

Students will learn and understand: 

  • The concept and process of a chemical reaction induced by the passage of an electric current through water. 
  • The chemistry behind the addition of the common salt in water and how to trap the gases released from the electrodes.   
  • The correlation between electrolysis and Faraday’s 1st law of electrolysis. 
  • The factors that influence the efficiency and the applications of the electrolysis.