Materials advances result from study of cold fusion

Abstract

I 1989, electrochemists Stanley Pons and Martin Fleischmann, working at The University of Utah, astounded the scientific world by announcing that they had achieved nuclear fusion of hydrogen isotopes—the process that powers stars—in a simple benchtop experiment. They claimed to have seen evidence of fusion, in particular a heat output greater than the energy input to the apparatus, when they electrolyzed deuterated lithium hydroxide in heavy water using palladium electrodes. The claim created excitement, controversy, and even outrage. For one thing, the “breakthrough” was announced not in a scientific paper but in a press conference—then still a highly irregular departure from scientific protocol. Pons and Fleischmann released only the sketchiest details of their experimental procedure and results for what became known as “cold fusion,” and even these details seemed to change as the claims were probed and challenged. Some other researchers reported similar findings, but several large-scale efforts to replicate the Utah work failed to see “excess heat” or any other evidence of fusion. The work came to be widely regarded as a textbook case of “pathological,” irreproducible science; some even suspected fraud. All the same, cold fusion has never gone away. A few researchers, working at the fringes of the scientific community, have continued to claim to see tantalizing signs that there really is something in it after all. However, the field has never shaken off its bad reputation. There was much surprise when in June, 30 years after the original event, Nature published an article by a team of researchers funded by Google describing renewed searches for “low-energy” fusion of hydrogen isotopes (deuterium, which has a lower energy threshold for fusion than hydrogen-1) using palladium electrodes.1 The paper reported no evidence of such a process in electrochemical experiments similar to those of Pons and Fleischmann, but it described a low level of fusion from a different experimental setup in which a plasma of deuterium ions surrounded a negatively charged palladium wire. The new findings will not persuade anyone that Pons and Fleischmann were right, but they could give cold fusion a new lease on life. Moreover, the study showed that there are interesting things still to learn about the materials science of the palladium–hydrogen system. That is what attracted materials researcher Yet-Ming Chiang of the Massachusetts Institute of Technology (MIT) in Cambridge, Mass., to the collaboration. Chiang says that he and the other research team members were recruited by Matt Trevithick, a former MIT graduate and now a program manager at Google Research in Mountain View, Calif., who is a co-author of the article. Trevithick had maintained an interest in cold fusion ever since the story broke. Chiang, in contrast, says that he paid it rather little heed at the time, when he had only recently become a faculty member at MIT. At that stage, Chiang was busy with hightemperature superconductivity, being on one of the teams that formed the spinout company American Superconductor. When Trevithick contacted him to ask if he would be interested in looking into cold fusion, Chiang had no strong preconceptions. Their co-author, electrochemist Curtis Berlinguette of The University of British Columbia in Vancouver, Canada, meanwhile, was genuinely enthusiastic about the prospect. “Renewable energy and fusion technologies are not scaling at the pace we need them to,” says Berlinguette. “If cold fusion were realizable, it could take the world into an era of energy surplus rather than scarcity. It therefore seemed irresponsible to not take another look at it. For me, cold fusion started in 2015,” says Berlinguette. “Prior to that, I didn’t know enough about it to have an opinion. I was driven simply by curiosity to learn more about the field.” Although the research team began by consulting leading figures in the cold-fusion community and designing replication studies, “we quickly started designing entirely new experiments to better inform the materials and physics space relevant to cold-fusion research,” says Berlinguette. “Our overarching objective was to conduct hypothesis-driven research that could be published in top science journals.” For Chiang, there was the possibility of delving into some interesting materials science—in particular, the remarkable capacity of palladium to absorb hydrogen. “Palladium is not the only material that will absorb hydrogen at high concentrations, but it is the exemplar,” says Chiang. He saw a clear connection to his work on ion-insertion compounds for batteries. Electrochemistry, he says, is known to be an extremely powerful driving force for loading ions or atoms into such materials. Could they harness that force to get higher concentrations of hydrogen into the metal? That alone would not guarantee fusion, though. “There were several hypotheses mixed up in the original proposal,” says electrochemist David Williams of The University of Auckland in New Zealand, who led a major British attempt to replicate the claims of Pons and Fleischmann in 1989. “First there was the idea that loading hydrogen into palladium would obtain a sufficient density to trigger fusion reactions,” which he says was based on flawed assumptions. “Hidden inside this hypothesis was an assumption