Because the name suggests, most electronic devices today work through the movement of electrons. But materials that may efficiently conduct protons — the nucleus of the hydrogen atom — might be key to plenty of essential technologies for combating global climate change.
Most proton-conducting inorganic materials available now require undesirably high temperatures to attain sufficiently high conductivity. Nevertheless, lower-temperature alternatives could enable quite a lot of technologies, comparable to more efficient and sturdy fuel cells to provide clean electricity from hydrogen, electrolyzers to make clean fuels comparable to hydrogen for transportation, solid-state proton batteries, and even latest sorts of computing devices based on iono-electronic effects.
With a view to advance the event of proton conductors, MIT engineers have identified certain traits of materials that give rise to fast proton conduction. Using those traits quantitatively, the team identified a half-dozen latest candidates that show promise as fast proton conductors. Simulations suggest these candidates will perform much better than existing materials, although they still should be conformed experimentally. Along with uncovering potential latest materials, the research also provides a deeper understanding on the atomic level of how such materials work.
The brand new findings are described within the journal , in a paper by MIT professors Bilge Yildiz and Ju Li, postdocs Pjotrs Zguns and Konstantin Klyukin, and their collaborator Sossina Haile and her students from Northwestern University. Yildiz is the Breene M. Kerr Professor within the departments of Nuclear Science and Engineering, and Materials Science and Engineering.
“Proton conductors are needed in clean energy conversion applications comparable to fuel cells, where we use hydrogen to provide carbon dioxide-free electricity,” Yildiz explains. “We would like to do that process efficiently, and subsequently we’d like materials that may transport protons very fast through such devices.”
Present methods of manufacturing hydrogen, for instance steam methane reforming, emit an incredible deal of carbon dioxide. “One method to eliminate that’s to electrochemically produce hydrogen from water vapor, and that needs superb proton conductors,” Yildiz says. Production of other essential industrial chemicals and potential fuels, comparable to ammonia, will also be carried out through efficient electrochemical systems that require good proton conductors.
But most inorganic materials that conduct protons can only operate at temperatures of 200 to 600 degrees Celsius (roughly 450 to 1,100 Fahrenheit), and even higher. Such temperatures require energy to keep up and could cause degradation of materials. “Going to higher temperatures is just not desirable because that makes the entire system more difficult, and the fabric durability becomes a problem,” Yildiz says. “There is no such thing as a good inorganic proton conductor at room temperature.” Today, the one known room-temperature proton conductor is a polymeric material that is just not practical for applications in computing devices because it might probably’t easily be scaled all the way down to the nanometer regime, she says.
To tackle the issue, the team first needed to develop a basic and quantitative understanding of exactly how proton conduction works, taking a category of inorganic proton conductors, called solid acids. “One has to first understand what governs proton conduction in these inorganic compounds,” she says. While taking a look at the materials’ atomic configurations, the researchers identified a pair of characteristics that directly pertains to the materials’ proton-carrying potential.
As Yildiz explains, proton conduction first involves a proton “hopping from a donor oxygen atom to an acceptor oxygen. After which the environment has to reorganize and take the accepted proton away, in order that it might probably hop to a different neighboring acceptor, enabling long-range proton diffusion.” This process happens in lots of inorganic solids, she says. Determining how that last part works — how the atomic lattice gets reorganized to take the accepted proton away from the unique donor atom — was a key a part of this research, she says.
The researchers used computer simulations to review a category of materials called solid acids that turn out to be good proton conductors above 200 degrees Celsius. This class of materials has a substructure called the polyanion group sublattice, and these groups must rotate and take the proton away from its original site so it might probably then transfer to other sites. The researchers were capable of discover the phonons that contribute to the pliability of this sublattice, which is crucial for proton conduction. Then they used this information to comb through vast databases of theoretically and experimentally possible compounds, searching for higher proton conducting materials.
In consequence, they found solid acid compounds which might be promising proton conductors and which were developed and produced for quite a lot of different applications but never before studied as proton conductors; these compounds turned out to have just the precise characteristics of lattice flexibility. The team then carried out computer simulations of how the particular materials they identified of their initial screening would perform under relevant temperatures, to verify their suitability as proton conductors for fuel cells or other uses. Sure enough, they found six promising materials, with predicted proton conduction speeds faster than one of the best existing solid acid proton conductors.
“There are uncertainties in these simulations,” Yildiz cautions. “I don’t need to say exactly how much higher the conductivity can be, but these look very promising. Hopefully this motivates the experimental field to attempt to synthesize them in several forms and make use of those compounds as proton conductors.”
Translating these theoretical findings into practical devices could take some years, she says. The likely first applications can be for electrochemical cells to provide fuels and chemical feedstocks comparable to hydrogen and ammonia, she says.
The work was supported by the U.S. Department of Energy, the Wallenberg Foundation, and the U.S. National Science Foundation.
