Concentration Cell

Concentration cells can be defined as electrochemical cells that consist of two half-cells wherein the electrodes are the same, but they vary in concentration. A concentration cell acts to dilute the more concentrated solution and concentrate the more dilute solution, creating a voltage as the cell reaches an equilibrium. This is achieved by transferring the electrons from the cell with the lower concentration to the cell with the higher concentration. A Concentration cell consists of a salt bridge, electrode and voltmeter.

Types of Concentration Cells

Concentration cells can be classified into two types-
1. Electrode Concentration Cells
2. Electrolyte Concentration Cells

1. Electrode Concentration Cells

These cells consist of same solutions used as electrolytes in each half-cell. However, the half-cells differ in the concentration of the electrode (the electrodes are made up of the same material).
An Example for this type of cell would be a cell consisting of two hydrogen electrodes which are subjected to varying pressures but are immersed in the same solutions (containing hydrogen ions).
(Pt: H₂ (Pressure p₁)) / Anode |H⁺ || (H₂ (Pressure p₂) Pt) / Cathode Pt: H₂(p₁) | H⁺ ions solution | H₂(p₂): Pt

2. Electrolyte Concentration Cells

These cells consist of same electrodes immersed in the solutions of the same electrolytes but with varying concentrations. In these cells, the electrolyte tends to diffuse from higher concentration solutions towards solutions of lower concentration.
An example for this type of cell is a cell where the anode consists of Zn/Zn²⁺(0.1M) whereas the cathode consists of Zn²⁺(0.01M)/Zn. In this cell, the flow of electrons from the anode to the cathode is due to the reduction of Zn²⁺ ions at the cathode into metallic zinc.
(Zn|Zn²⁺ (C₁)) / Anode || (Zn²⁺ (C₂)|Zn) / Cathode