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A cathode is a negatively charged metal electrode from which conventional current travels in a polarized electrical device. It attracts positive charge or cations. The behavior of the cathode is the opposite to that of an anode. In a polarized electrical device, a cathode is considered the electron donor or the source of electrons.
A cathode is a negatively charged electrode. However, the polarity of the cathode with respect to anode can either be negative or positive, and it largely depends on the operation of the device. For example, in a recharging battery the cathode is negative. However in the case of discharging a battery, the cathode polarity is positive. In general, in a device the cathode is the terminal from which the current flows out, whereas the anode is the terminal from which the current flows in from outside.
In chemistry, the cathode is considered as the electrode at which the electrochemical reduction takes place. The distinction between cathode and anode is purely based on the current and not on voltage. The metal used for the cathode has a significantly higher number of electrons than neutrons or protons. In most applications, the cathode gains mass over time due to the gain of cations. The electrons from the cathode repel each other, and thus move away from the cathode, reaching the anode, which has the opposite polarity. Thus, cathodes along with anodes occupy important roles in the production of electrochemical reactions.