New study tracks fundamental movements in energy conversion

Energy conversion processes, from photosynthesis and respiration in living organisms to combustion and fuel cells used to power the world, require the orchestrated movement of electrons and protons. Yet understanding that movement has remained elusive.

A study by researchers at Yale and in Sweden provides a new understanding of the fundamental principles of electron and proton movement that could enable the design of new technologies that harness solar energy and convert it into fuels.

The study appears in the journal Science. It comes from the labs of chemistry professors James Mayer and Sharon Hammes-Schiffer of Yale and chemistry professor Leif Hammarström of Uppsala University. The first author of the study is Giovanny Parada, a postdoctoral associate in Mayer’s lab.

Their research focuses on a counterintuitive effect known as the “Marcus inverted region,” in which an electron transfer reaction slows down when it becomes very thermodynamically favorable. The Marcus inverted region is considered central to the efficiency of photosynthesis, scientists say, because it slows down energy processes that are wasteful.

In the new study, the researchers observed a similar effect for the concerted movement of an electron and proton.

“We studied molecules capable of forming highly energetic states upon light irradiation, much like the states in photosynthesis that store light energy,” said Mayer, the Charlotte Fitch Roberts Professor of Chemistry at Yale. “The molecules allow us to investigate how the speed of concerted electron and proton movement changes with respect to its energy requirement. Using time-resolved laser experiments, we demonstrate an inverted region regime for concerted electron and proton movement for the first time.”

“We showed that concerted electron and proton movement can access inverted region regimes and therefore that these reactions could be at play in photosynthetic energy conversion,” said Hammes-Schiffer, the John Gamble Kirkwood Professor of Chemistry at Yale. “These types of reactions could be utilized to design solar cells and other energy conversion devices.”

Additional authors of the work were Yale graduate students Zachary Goldsmith and Scott Kolmar, Yale research support specialist Brandon Mercado, and doctoral student Belinda Pettersson Rimgard of Uppsala University.