"Cold fusion is a hypothetical type of nuclear reaction that would occur at, or near, room temperature, compared with temperatures in the millions of degrees that are required for "hot" fusion, which takes place naturally within stars. There is currently no accepted theoretical model which would allow cold fusion to occur.
In 1989 Martin Fleischmann (then one of the world's leading electrochemists) and Stanley Pons reported that their apparatus had produced anomalous heat ("excess heat"), of a magnitude they asserted would defy explanation except in terms of nuclear processes. They further reported measuring small amounts of nuclear reaction byproducts, including neutrons and tritium. The small tabletop experiment involved electrolysis of heavy water on the surface of a palladium (Pd) electrode. The reported results received wide media attention, and raised hopes of a cheap and abundant source of energy.
Many scientists tried to replicate the experiment with the few details available. Hopes fell with the large number of negative replications, the withdrawal of many positive replications, the discovery of flaws and sources of experimental error in the original experiment, and finally the discovery that Fleischmann and Pons had not actually detected nuclear reaction byproducts. By late 1989, most scientists considered cold fusion claims dead, and cold fusion subsequently gained a reputation as pathological science. In 1989, a review panel organized by the United States Department of Energy (DOE) found that the evidence for the discovery of a new nuclear process was not persuasive enough to start a special program, but was "sympathetic toward modest support" for experiments "within the present funding system." A second DOE review, convened in 2004 to look at new research, reached conclusions similar to the first. Support within the then-present funding system did not occur."
Cold fusion - Wikipedia, the free encyclopedia
"Nuclear fusion and nuclear fission are two different types of energy-releasing reactions in which energy is released from high-powered atomic bonds between the particles within the nucleus. The main difference between these two processes is that fission is the splitting of an atom into two or more smaller ones while fusion is the fusing of two or more smaller atoms into a larger one."
Nuclear Fission vs Nuclear Fusion - Difference and Comparison | Diffen
So, how does a theoretical cold fusion device create fission?