Intrinsic nonequilibrium distribution of large ions in charged small nanopores

TL;DR

This paper experimentally demonstrates that large ions in small nanopores exhibit a nonequilibrium distribution that produces a potential difference exceeding thermodynamic limits, challenging traditional second law constraints.

Contribution

It provides experimental validation of intrinsic nonequilibrium ion distributions in nanopores, supporting theoretical predictions about breaking thermodynamic bounds.

Findings

Measured potential difference exceeds second law limits by nearly an order of magnitude.

Large ions in small nanopores show a nonequilibrium distribution due to confinement effects.

Experimental results align with molecular dynamics simulations of similar systems.

Abstract

Recent theoretical research on the fundamentals of statistical mechanics has led to a remarkable discovery [2-4]: with a locally nonchaotic energy barrier, a macroscopic system may produce useful work in a cycle by absorbing heat from a single thermal reservoir without any other effect, thereby breaking the boundaries of the second law of thermodynamics. The mechanism is rooted in the intrinsic nonequilibrium steady state associated with local nonchaoticity. In the current investigation, we experimentally validate this concept, with the weak gravitational force in the "toy model" being changed to the strong Coulomb force. The tests are performed on a set of nanoporous carbon electrodes immersed in aqueous cesium pivalate solutions. The key characteristic is that the effective nanopore size is only slightly larger than the effective ion size, less than twice the ion size. At first glance, the supercapacitive cells exhibit "normal" charge curves. However, the steady-state distribution of the large ions in the charged small nanopores inherently differs from thermodynamic equilibrium, because of the confinement effect of the nanopore walls. The measured potential difference is nearly one order of magnitude larger than the upper limit calculated from the heat-engine statement of the second law of thermodynamics. Although counterintuitive, such a phenomenon is consistent with the molecular dynamics simulations in open literature.