Cold fusion

Cold fusion is a hypothesized type of nuclear reaction. It is theorized to occur at or near room temperature. This concept differs greatly from thermonuclear fusion. Thermonuclear fusion is the process that powers stars and occurs in hydrogen bombs. That process requires temperatures of millions of degrees. Cold fusion would be a much calmer version of this energy release. Currently, there is no accepted theoretical model to explain how it could happen. If it were possible, it could provide a cheap and abundant source of energy.

The mechanism involves a process called electrolysis. In these experiments, researchers use a palladium (Pd) electrode. They place this electrode into a container of heavy water. This container is a calorimeter, which is an insulated vessel used to measure heat. Heavy water contains deuterium, an isotope of hydrogen. The researchers apply a continuous electric current to the liquid for many weeks. They hypothesized that the high compression and mobility of deuterium within the palladium metal might trigger fusion. During the process, the temperature of the cell might stay stable at 30 °C. However, the temperature could suddenly rise to about 50 °C. This sudden rise creates what researchers call "excess heat." This heat is significantly higher than the electrical power put into the system.

There are different ways to think about these nuclear reactions. One known method is muon-catalyzed fusion. This is a way to induce fusion without high temperatures using muons. Another concept is geo-fusion, which involves fusion in a planetary core. Some researchers now use different names for these phenomena. They call them low-energy nuclear reactions (LENR). Others call them condensed matter nuclear science (CMNS). These terms help distinguish the work from traditional thermonuclear fusion.

The history of these ideas dates back much further than 1989. In the 19th century, Thomas Graham recognized that palladium could absorb hydrogen. In the late 1920s, Friedrich Paneth and Kurt Peters reported hydrogen transforming into helium. They claimed this happened through nuclear catalysis in palladium at room temperature. However, they later retracted their report. They found the helium came from the air instead. In 1927, John Tandberg also reported fusing hydrogen into helium using an electrolytic cell. He even applied for a Swedish patent to produce helium and reaction energy. His patent was denied because he could not explain the physical process.

The most famous event occurred in March 1989. Electrochemists Martin Fleischmann and Stanley Pons announced their findings. They claimed their apparatus produced excess heat through nuclear processes. They also reported measuring neutrons and tritium. Tritium is a form of hydrogen produced by the fusion of deuterium. These findings caused a massive media sensation. People hoped for a limitless source of clean energy using only seawater. This hope was high because of the 1973 oil crisis and concerns about global warming.

However, the scientific response was largely negative. Many physicists tried to replicate the results but failed. They identified methodological flaws and experimental errors in the original study. By late 1989, most scientists considered the claims dead. The field gained a reputation as pathological science. In 1989, the United States Department of Energy (DOE) reviewed the evidence. They concluded it was not convincing and decided against funding. A second DOE review in 2004 reached the same conclusion. Most research on this topic is no longer published in mainstream peer-reviewed journals.

Despite this, a small community of interest remains. There are between 100 and 200 researchers still investigating these effects. They continue to present work at meetings like the American Chemical Society. Even in 2019, a failed replication attempt was published in the journal Nature. These researchers believe there is too much evidence of unusual effects to ignore. They continue to search for a way to prove these reactions can truly occur.