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. When setting up a salt bridge between different solvents of half-cells, it is crucial to ensure that the electrolyte used in the bridge is soluble in both solutions and does not interact with any species present in either solutions.

A salt bridge filled with a solution of a single salt minimizes the liquid junction potential most efficiently when the following conditions are met:

Traditionally, concentrated aqueous potassium chloride (KCl) solution has been most often used to minimize the liquid-junction potential. When comparing other salt solutions such as potassium bromide and potassium iodide to potassium chloride, potassium chloride is the most efficient in nullifying the junction potential. Yet, the effectiveness of this salt bridge decreases as the ionic strength of the working solutions (catholyte and anolyte) increases.

There are several designs of salt bridges: glass tube bridges (traditional KCl-type salt bridge and ionic liquid salt bridge, as shown in the Figure), filter paper bridges, porous frit salt bridges, fumed-silica, and agar gel salt bridges.

Glass tube salt bridges commonly consist of U-shaped Vycor tubes filled with a relatively inert electrolyte. 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 combination is chosen which does not react with any of the chemicals used in the cell.

Due to the numerous drawbacks of KCl-type salt bridges, ionic liquid salt bridges (ILSB) have been utilized to address the potentiometry issues arising from KCl-type salt bridges in electrochemical cells. ILSBs demonstrate efficient performance in aqueous solutions of hydrophilic electrolytes. This is because ionic liquids do not mix with water (they are immiscible), rendering them suitable as salt bridges for aqueous solutions. Additionally, they are chemically inert and highly stable in water.

To set up a glass tube salt bridge, a U-shaped Vycor tube is fashioned to contain a suitable electrolyte solution. Normally, glass frits, a porous material, cover the ends of the tube or the electrolyte is often gelified with agar-agar to help prevent the intermixing of fluids that might otherwise occur.