Understanding the electric double layer (EDL) of aqueous electrolytes near the carbon interface is critical for optimizing device performance in a wide variety of emerging technologies, including water desalination and supercapacitors for energy storage. However, despite considerable theoretical and experimental efforts, a final consensus has not been reached on the behavior of simple ions, such as alkali cations, at the graphitic interface. This key knowledge gap becomes even more significant for solutions in carbon nanopores, where the paramount important effects of confinement must be taken into account. Here, we integrate high-level first-principles simulations with electrochemical measurements to unravel the key features of the EDL of several aqueous solutions at the interface with graphene and under confinement within carbon slit-pores. We find that large, strongly polarized cations with weak hydration energy exhibit a stronger affinity to the graphene interface. In addition, space charge transfer (SCT) effect was found to have substantial impact on the electrochemical interface, which was often neglected in conventional force field simulations, and essential to reproduce the capacitive behavior of the interface observed experimentally. These effects are dramatically enhanced by nanoconfinement, which can be ultimately related to the intrinsic properties of the ions and the nature of their solvation. Our study points to the complex interplay between confinement and specific ion effects on the interfacial capacitance and ion accessibility, suggesting general improvement strategies for optimizing carbon-based materials for energy storage and water desalination technologies.

Interplay between specific-ion effects and confinement in the aqueous electric double layer

2019 Fall National Meeting

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