thumb|An electrochemical cell (resembling a [[Daniell cell) with a filter paper salt bridge. The paper has been soaked with a Potassium nitrate solution.]]
In electrochemistry, a salt bridge or ion bridge is an essential laboratory device to minimize the liquid junction potential in an electrochemical cell. The salt bridge has been in use for more than 100 years. It contains an electrolyte solution, typically an inert solution, used to connect the oxidation and reduction half-cells of a galvanic cell (voltaic cell), a type of electrochemical cell. In short, it functions as an ionically-conducting link connecting the anode and cathode half-cells within the electrochemical cell. It also minimizes and stabilizes the liquid junction potential between the solutions in the half-cells. Additionally, it can be used to minimize cross-contamination between the two half cells.
As shown in the figure on the right, a salt bridge typically consists of tubes filled with an electrolyte solution. These tubes often have diaphragms - such as glass frits - at their ends to help contain the solution within the tubes and prevent excessive mixing with the surrounding environment.
- The salt concentration in the ion bridge is much higher than in the working solutions, which it connects. This minimizes the effects of the catholyte and anolyte compositions on the measured voltage difference.
Traditionally, concentrated aqueous potassium chloride (KCl) solution has been most often used to minimize the liquid-junction potential. The electrolyte solution usually comprises a combination of cations, such as ammonium and potassium, and anions, including chloride and nitrate, which have similar mobility.
The conductivity of this kind of salt bridge depends on a number of factors: the concentration of the electrolyte solution, the texture of the paper, and the absorbing ability of the paper. Generally, smoother texture and higher absorbency equate to higher conductivity. This filter paper can now be used to act as a salt bridge and connect the two half-cells.
thumb|Charcoal (black box at the bottom of the cell) acts as a salt bridge to allow ion transfer.
A porous junction serves as a salt bridge between the two half-cells of reference and electrolyte solutions.