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Institute of Physics

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05/31/2017

New paper published in Physical Chemistry Chemical Physics (PCCP)

A detailed technical description of the recently published in situ SAXS and atomistic modeling approach is given in this paper. In addition an alternative strategy to derive pore size distributions from ex situ SAXS measurements and novel aspects regarding ion kinetics in nanoporous carbon supercapacitors are presented.

Besides the detailed technical description of the recently published in situ SAXS and modeling toolkit (C.Prehal et al.; doi:10.1038/nenergy.2016.215) we were able to derive length scale dependent information of ion kinetics during the electrosorption process. Using ex situ SAXS measurements and the concept of Gaussian random fields (GFR) a novel strategy to derive pore size distributions of microporous carbons. Compared to pore size distributions obtained from gas sorption analysis, no inherent assumption about the pore shape is required.

 

Link to publication: http://pubs.rsc.org/en/Content/ArticleLanding/2017/CP/C7CP00736A

 

Abstract:

A new carbon model derived from in situ small-angle X-ray scattering (SAXS) enables a quantitative description of the voltage-dependent arrangement and transport of ions within the nanopores of carbon-based electric double-layer capacitors. In the first step, ex situ SAXS data for nanoporous carbon-based electrodes are used to generate a three-dimensional real-space model of the nanopore structure using the concept of Gaussian random fields. This pore model is used to derive important pore size characteristics, which are cross-validated against the corresponding values from gas sorption analysis. In the second step, simulated in situ SAXS patterns are generated after filling the model pore structure with an aqueous electrolyte and rearranging the ions via a Monte Carlo simulation for different applied electrical potentials. These simulated SAXS patterns are compared with in situ SAXS patterns recorded during voltage cycling. Experiments with different cyclic voltammetry scan rates revealed a systematic time lag between ion transport processes and the applied voltage signal. Global transport into and out of nanopores was found to be faster than the accommodation of the local equilibrium arrangement in favor of sites with a high degree of confinement

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