In the 1989 Fleischmann–Pons experiment, the researchers claimed that electrolysis produced cold fusion.
Martin Fleischmann and Stanley Pons announced that palladium electrodes loaded with deuterium during heavy-water electrolysis generated excess heat. They interpreted the heat as evidence of nuclear fusion occurring under conditions far milder than those in stars or conventional fusion devices.
The announcement attracted intense attention because, if confirmed, it would have implied a compact source of nuclear energy. However, many laboratories could not reproduce the reported effect, and the claim did not become accepted as a demonstrated source of fusion energy.
Cold fusion is therefore the claimed phenomenon, not an established result comparable to hot-fusion experiments. Another common mix-up is to call the work nuclear fission: fusion combines light nuclei, whereas fission splits heavy nuclei. The episode remains a major example of the importance of independent replication.