A galvanic cell forces electrons to travel through a wire rather than moving directly between chemicals. Every working cell setup requires two separate sides that chemists call half-cells. Each half-cell contains a solid piece of metal called an electrode.
These metal electrodes sit in a liquid mixture filled with moving ions. A wire connects the two metal pieces to let electrons flow freely. One electrode is called the anode, and it carries a negative charge.
At the anode, a chemical loses its electrons in a process called oxidation. These freed electrons travel through the outer wire toward the other side. They arrive at the positive electrode, which chemists call the cathode.
At the cathode, a different chemical grabs the electrons in a process called reduction. The continuous flow of electrons through the wire provides the usable electric current. The cell also needs a salt bridge connecting the two liquid mixtures.
The salt bridge lets ions cross over to balance the electrical charges. Without this bridge, electric charge builds up and the battery instantly dies. Because the chemical reaction happens naturally, it has a negative Gibbs free energy.