Abstract
The transport of protons is critical in a variety of bio- and electro-chemical processes and technologies. The Grotthuss mechanism is considered to be the most efficient proton transport mechanism, generally implying a transfer of protons between ‘chains’ of host molecules via elementary reactions within the hydrogen bonds. Although Grotthuss proposed this concept more than 200 years ago, only indirect experimental evidence of the mechanism has been observed. Here we report the first experimental observation of proton transfer between the molecules in pure and 85% aqueous phosphoric acid. Employing dielectric spectroscopy, quasielastic neutron, and light scattering, and ab initio molecular dynamic simulations we determined that protons move by surprisingly short jumps of only ~0.5–0.7 Å, much smaller than the typical ion jump length in ionic liquids. Our analysis confirms the existence of correlations in these proton jumps. However, these correlations actually reduce the conductivity, in contrast to a desirable enhancement, as is usually assumed by a Grotthuss mechanism. Furthermore, our analysis suggests that the expected Grotthuss-like enhancement of conductivity cannot be realized in bulk liquids where ionic correlations always decrease conductivity.
| Original language | English |
|---|---|
| Article number | 77 |
| Journal | Communications Chemistry |
| Volume | 6 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 2023 |
Funding
We thank Drs. Linas Vilčiauskas (Vilnius University), Klaus-Dieter Kreuer (MPI-Stuttgart) and Mark E. Tuckerman (NYU) for helpful discussions and insight comments. We acknowledge support by the National Science Foundation (awards CHE-1764409 and CHE-2102425) for dielectric and simulations work. I.P., R.L.S. and E.M. acknowledge support for neutron and some dielectric studies by the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Research at the BASIS of the ORNL’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Computing resources were provided through an XSEDE allocation DMR130078 on Stampede2 at the Texas Advanced Computing Center (TACC). We thank Drs. Linas Vilčiauskas (Vilnius University), Klaus-Dieter Kreuer (MPI-Stuttgart) and Mark E. Tuckerman (NYU) for helpful discussions and insight comments. We acknowledge support by the National Science Foundation (awards CHE-1764409 and CHE-2102425) for dielectric and simulations work. I.P., R.L.S. and E.M. acknowledge support for neutron and some dielectric studies by the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Research at the BASIS of the ORNL’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Computing resources were provided through an XSEDE allocation DMR130078 on Stampede2 at the Texas Advanced Computing Center (TACC).