15.1-Electrolysis

Electrolysis for the future

• Electrolysis is a promising option for carbon-free hydrogen production from renewable and nuclear resources.

• Electrolysis is the process of using electricity to split water into hydrogen and oxygen.

• This reaction takes place in a unit called an electrolyzer.

• Electrolyzers can range in size from small, appliance-size equipment that is well-suited for small-scale distributed hydrogen production to large-scale, central production facilities that could be tied directly to renewable or other non-greenhouse-gas-emitting forms of electricity production.

How Does it Work?

• Like fuel cells, electrolyzers consist of an anode and a cathode separated by an electrolyte.

• Different electrolyzers function in different ways, mainly due to the different type of electrolyte material involved and the ionic species it conducts.

15.2-Electrolysis of Aqueous Solutions

Components of an Aqueous Solution

• Electrolytes are aqueous or molten.

  • In order for electrolysis to occur, compound must be dissolved in water, or melted to form a liquid.

  • This means that the ions are free to move around when a current is applied.

• Aqueous electrolytes contain water.

  • When a compound is dissolved in water, the resulting solution has water present.

  • This means that there is both the ionic compound and water molecules in the solution.

• Water splits into ions.

  • Water molecules can split into two ions: hydrogen ions (H+) and hydroxide ions (OH–). When joined together, they produce water molecules, H2O.

Ion Production with Aqueous Electrolytes

• When aqueous electrolytes are involved, electrolysis is slightly more complicated.

• Two ions are attracted to the cathode.

  • The hydrogen ion and the metal ion are attracted to the cathode. To decide what substance is made at the cathode, we must use the reactivity series.

• Metal reactivity is compared to hydrogen.

  • If the metal element formed during electh

  • Electrolysis is more reactive than hydrogen, then hydrogen will be produced at the cathode.

  • If the metal element formed is less reactive than hydrogen, then the metal is produced at the cathode.

• Two ions are attracted to the anode.

  • The hydroxide ions and halide ions are attracted to the anode.

  • If both are present, then a halogen is formed.If no halide ions are present, then the hydroxide ions are  discharged, and oxygen is formed.

Practice Questions:

• The electrolysis of aluminium oxide is an expensive process. Suggest two reasons why

  • Because a various electricity is required in extraction process. Aluminium is most abundant and is metal in the Earth’ crust

• In electrolysis, what is the name of the negative electrode?

  • Cathode

• What happens at the anode during electrolysis?

  • Negative ions lose electrons

• What is reduction?

  • Gain of electrons