Michael Faraday had constructed Faraday's disk to demonstrate and visualise the theory about currents and magnetic fields he had discovered. Unfortunately, the disk was very inefficient in producing current and was never actually used as a practical power source, but only as a tool of demonstration.
Other scientists, with Nikola Tesla amongst them as one of the earliest to take profit of Faraday's invention, later improved and changed Faraday's disk. Tesla patented a version of Faraday's disk which had less frictional losses and Hippolyte Pixii constructed the first efficient dynamo by adding a commutator to it. Sir Mark Oliphant was inspired by it to build what became the world's largest homopolar generator (producing 500 Megajoules).
Faraday's disk helped a wide range of scientists, such as Sir Joseph Larmour, to understand more phenomena. In Larmour's case, the newly found link between magnetic fields and current lead him to an explanation of several phenomena related to sunspots.
Zénobe Gramme used the principle of Faraday's disk to design the first commercial power plants in Paris, discovering what is since then known as the basic concept of a spinning endless loop of wires.
Later, Joseph Newmann invented the axletree dynamo, which was believed to be a perpetual motion dynamo but was never patented.