Effect of Strong Acid Functional Groups on Electrode Rise Potential in Capacitive Mixing by Double Layer Expansion

Marta C. Hatzell, Muralikrishna Raju, Valerie J. Watson, Andrew G. Stack, Adri C. T. van Duin, Bruce E. Logan

Research output: Contribution to journalArticlepeer-review

50 Scopus citations


© 2014 American Chemical Society. The amount of salinity-gradient energy that can be obtained through capacitive mixing based on double layer expansion depends on the extent the electric double layer (EDL) is altered in a low salt concentration (LC) electrolyte (e.g., river water). We show that the electrode-rise potential, which is a measure of the EDL perturbation process, was significantly (P = 10$^{-5}$) correlated to the concentration of strong acid surface functional groups using five types of activated carbon. Electrodes with the lowest concentration of strong acids (0.05 mmol g$^{-1}$) had a positive rise potential of 59 ± 4 mV in the LC solution, whereas the carbon with the highest concentration (0.36 mmol g$^{-1}$) had a negative rise potential (-31 ± 5 mV). Chemical oxidation of a carbon (YP50) using nitric acid decreased the electrode rise potential from 46 ± 2 mV (unaltered) to -6 ± 0.5 mV (oxidized), producing a whole cell potential (53 ± 1.7 mV) that was 4.4 times larger than that obtained with identical electrode materials (from 12 ± 1 mV). Changes in the EDL were linked to the behavior of specific ions in a LC solution using molecular dynamics and metadynamics simulations. The EDL expanded in the LC solution when a carbon surface (pristine graphene) lacked strong acid functional groups, producing a positive-rise potential at the electrode. In contrast, the EDL was compressed for an oxidized surface (graphene oxide), producing a negative-rise electrode potential. These results established the linkage between rise potentials and specific surface functional groups (strong acids) and demonstrated on a molecular scale changes in the EDL using oxidized or pristine carbons.
Original languageEnglish (US)
Pages (from-to)14041-14048
Number of pages8
JournalEnvironmental Science & Technology
Issue number23
StatePublished - Nov 17 2014
Externally publishedYes

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-I1-003-13
Acknowledgements: This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program to M.C.H. under Grant No. (NSF) DGE1255832, and a grant from the King Abdullah University of Science and Technology (KAUST) (Award KUS-I1-003-13). A.C.T.V.D. and M.R. conducted reactive force field modeling with support from the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. A.G.S. conducted metadynamics modeling with support from the Division of Chemical Sciences, Geosciences and Biosciences, Office of Science, Office of Basic Energy Sciences, U.S. Department of Energy.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.


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