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

Abstract

We report that 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 themore » 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. In conclusion, 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.« less

Authors:

Hatzell, Marta C. ^[1]; Raju, Muralikrishna ^[2]; Watson, Valerie J. ^[3]; Stack, Andrew G. ^[4]; van Duin, Adri C. T. ^[1]; Logan, Bruce E. ^[3]

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+ Show Author Affiliations

1. Pennsylvania State Univ., University Park, PA (United States). Dept of Mechanical Engineering
2. Pennsylvania State Univ., University Park, PA (United States). Dept of Physics
3. Pennsylvania State Univ., University Park, PA (United States). Dept of Civil and Environmental Engineering
4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division

Publication Date:

Mon Nov 03 00:00:00 EST 2014

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1286802

Grant/Contract Number:  

AC05-00OR22725; DGE1255832; KUS-I1- 384 003-13

Resource Type:

Accepted Manuscript

Journal Name:

Environmental Science and Technology

Additional Journal Information:

Journal Volume: 48; Journal Issue: 23; Journal ID: ISSN 0013-936X

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY