The first fuel cell was used in the form of a gas voltaic battery.
William Robert Grove discovered that by immersing the first ends of two platinum electrodes in sulfuric acid and the other ends in oxygen and hydrogen, a constant current would flow between the electrodes. The sealed containers held water as well as the gases, and he noted that the water level rose in both tubes as the current flowed. By combining several sets of these electrodes in a series circuit, he created what he called a "gas battery" which became known as the first fuel cell.
A fuel cell is an electrochemical energy conversion device. A fuel cell converts the chemicals hydrogen and oxygen into water and in the process produces electricity. Grove’s fuel cell functioned as a power-generating unit that one can think of as an atomic sieve. The nuclei of hydrogen atoms pass through a plastic membrane, then combine with ambient oxygen to form water which is the fuel cell's only emission. The electrons are siphoned off as electricity. Fuel cells proved useful in the years following their discovery.