If the reactive components of an electrochemical cell are placed in contact with each other, they will react by direct transfer of electrons (an oxidation - reduction reaction) and there is no way to harness this energy to do electrical work.
Most metals corrode on contact with water (and moisture in the air), acids, bases, salts, oils, aggressive metal polishes, and other solid and liquid chemicals. Metals will also corrode when exposed to gaseous materials like acid vapors, formaldehyde gas, ammonia gas, and sulfur containing gases.