Galvanic Cells allow us to harness the electron flow in a redox reaction to perform useful work. Such cells find common use as batteries, pH meters, and as fuel cells. The setup of the cell, as seen in , requires that the oxidation and reduction half-reactions are connected by a wire and by a salt bridge or porous disk. Electrons will flow through that wire creating an electrical current. The salt bridge or porous disk allows the passage of ions in solution to maintain charge neutrality in each half-cell. Instead of drawing the setup of every cell like , chemists have devised a shorthand line notation discussed in Line Notation.
The direction of the current in a cell is determined by the standard reduction potential of each half-cell. For a reaction to be spontaneous, the overall cell potential must be positive (the rules for adding cell potentials are covered under Adding potentials). Therefore, the half-reaction with the greater reduction potential will be a reduction and the other half-reaction will be an oxidation. The electrode in the oxidation half-reaction is called the anode. The electrode in the reduction half-reaction is called the cathode.