According to most scientists, cold fusion

According to most scientists, cold fusion – a type of nuclear reaction that would occur at, or near, room temperature, is considered highly improbable or unproven with current understanding and technology.

The claim of cold fusion was famously made by Martin Fleischmann and Stanley Pons in 1989 when they reported producing excess heat that could only be explained by a nuclear process.

Their experimental results, however, could not be reliably reproduced by other scientists, which is a crucial criterion for scientific validation.

Most scientists assert that cold fusion contradicts established knowledge of nuclear physics. In conventional fusion, which powers the sun and thermonuclear weapons, nuclei of light elements like hydrogen overcome their natural repulsion (the Coulomb barrier) at extremely high temperatures and pressures to merge, releasing vast amounts of energy.

Achieving the necessary conditions for fusion on Earth typically requires massive facilities like tokamaks or inertial confinement devices that can sustain extremely high temperatures for a brief time.

Hence, while cold fusion - if it were possible- would be a revolutionary source of clean energy, the lack of reproducible evidence and theoretical support means that it remains a fringe area of study.