Journal
ACS NANO
Volume 8, Issue 3, Pages 2495-2503Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn406077n
Keywords
ion adsorption; small-angle neutron scattering; energy storage; porous carbon
Categories
Funding
- Army Research Office (ARO) [W911NF-12-1-0259]
- Laboratory Directed Research and Development Program
- Scientific User Facilities Division, Office of Basic Energy Sciences, US. Department of Energy
- NSF DMR [0922776]
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [0922776] Funding Source: National Science Foundation
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Experimental studies showed the impact of the electrolyte solvents on both the ion transport and the specific capacitance of microporous carbons. However, the related structure property relationships remain largely unclear and the reported results are inconsistent. The details of the interactions of the charged carbon pore walls with electrolyte ions and solvent molecules at a subnanometer scale are still largely unknown. Here for the first time we utilize in situ small angle neutron scattering (SANS) to reveal the electroadsorption of organic electrolyte ions in carbon pores of different sizes. A 1 M solution of tetraethylammonium tetrafluoroborate (TEATFB) salt in deuterated acetonitrile (d-AN) was used in an activated carbon with the pore size distribution similar to that of the carbons used in commercial double layer capacitors. In spite of the incomplete wetting of the smallest carbon pores by the d-AN, we observed enhanced ion sorption in subnanometer pores under the applied potential. Such results suggest the visible impact of electrowetting phenomena counterbalancing the high energy of the carbon/electrolyte interface in small pores. This behavior may explain the characteristic butterfly wing shape of the cyclic voltammetry curve that demonstrates higher specific capacitance at higher applied potentials, when the smallest pores become more accessible to electrolyte. Our study outlines a general methodology for studying various organic salts solvent carbon combinations.
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