Saltwater can serve as the electrolyte in a battery, thus generating electricity. A battery has three parts: an electrolyte and two electrodes, which are made of different materials, often metals. Some of the first batteries, made by Alessandro Volta around 1880, used saltwater, silver and zinc to generate electricity. This type of battery is easy to build and experiment with.
Electrolytes and Batteries
In water, table salt, or sodium chloride (NaCl), dissolves into positively charged sodium ions (Na+) and negatively charged chlorine atoms (Cl-). A solution of ions such as this is called an electrolyte. In a battery, one electrode -- called the cathode -- sheds electrons into the solution, leaving it with a positive charge. At the same time, the other electrode -- the anode -- collects electrons, giving it a negative charge. Ions in the electrolyte help facilitate this process. The charge imbalance between the two electrodes creates a electrical potential difference. If you connect the terminals in a circuit, the electrons built up in the anode will flow through the circuit back to the cathode, creating an electrical current.
Your Own Voltaic Pile
Volta made his "Voltaic Pile" battery with units consisting of saltwater-soaked paper sandwiched between a silver disk and a zinc disk. He stacked up this basic unit to create a battery with significant voltage. We now call such basic units cells. You can make a similar battery quite easily with household items. You will need five pennies made after 1982, cardstock or paperboard, salt, water, electrical tape, 120-grit sandpaper and two wires with stripped ends. Pennies made in 1983 and after are copper-coated zinc disks. Thanks to this fact, we don’t need two different types of metal disks as Volta did.
Building the Battery
Sand one side of four of the pennies all the way down to a flat zinc surface. Dissolve one tablespoon of salt in one cup of water (heating helps). From the cardstock, cut out four disks roughly the size of the pennies, and soak them in the salt water. Place one penny copper side down on the table and place a soaked disk on top of it. Continue stacking by alternating pennies and soaked disks, with the intact penny on top of the last soaked disk. Holding one wire on the first coin and one on the last coin, wrap electrical tape around the assembly to hold it together. Sealing the entire unit with tape will inhibit evaporation, making the battery last longer.
Using the Battery
Each cell, consisting of the zinc side of one penny, a soaked disk and the copper side of another penny, generates around one volt. With four cells, your battery will generate roughly four volts. You can test this with a multimeter. Also, four volts is enough to make an LED shine brightly. The short lead from the LED needs to be connected to the end of the battery that has the intact penny. This is the anode -- the negative pole of the battery.
Almost any combination of two different metals for the electrodes will make a battery. Different combinations yield different voltages. You can make a battery similar to Volta’s by stacking up cells made of saltwater-soaked cardstock sandwiched between two different metals. Ideas include pennies and nickels, pennies and aluminum (foil or sanded pieces of pop cans), pennies and zinc-coated washers, and uncoated steel washers and aluminum.