The specific energy of electrochemical double-layer capacitors (EDLCs) can be increased by design of the pore architecture to provide large interfaces between electrodes and electrolyte and efficient access to these surfaces. Colloidal-crystal templated carbon electrodes with interconnected, uniform mesopores have demonstrated high capacitances at fast charge/discharge rates in EDLCs used with ionic liquid electrolytes. Here we aim to enhance capacitive performance further through nitrogen doping, by combining a phenol-formaldehyde precursor with the ionic liquid (IL) 1-ethyl-3-methylimidazolium dicyanoamide (EMI-DCA) as the nitrogen source. The IL content in this precursor affects the resistance, structural integrity, and specific capacitance of the porous electrodes. With an IL content up to 50 wt%, the electrode resistance is reduced while the bicontinuous mesoporous structure of the resulting carbon is preserved. The specific capacitance of an electrode prepared with 50% IL in the precursor increases over 40% at 10 A g-1 compared to mesoporous carbons prepared using only the phenol-formaldehyde resol. With an ionic liquid electrolyte, the maximum specific capacitance is 237 F g-1 at 0.1 A g-1, and a specific capacitance of at least 195 F g-1 is maintained after 1000 cycles at 1 A g-1. A higher IL content in the precursor results in reduced structural order and capacitive performance.
Bibliographical noteFunding Information:
This work was supported by the University of Minnesota Initiative for Renewable Energy and the Environment (IREE). Portions of this work were carried out in the University of Minnesota Characterization Facility, which receives partial support from the NSF though the MRSEC, ERC, MRI, and NNIN programs. The funding sources had no involvement in the study design, collection, analysis and interpretation of data, writing of the manuscript, or decision to submit the article for publication. The authors would like to thank Professor Markus Antonietti of the MPI of Colloids and Interfaces, Potsdam, Germany, for helpful discussions.
© 2015 Elsevier B.V.
- Colloidal templating
- Electrochemical double-layer capacitor
- Ionic liquid
- Mesoporous carbon
- Nitrogen-doped carbon