title: Effect of strong acid functional groups on electrode rise potential in capacitive mixing by double layer expansion.
abstract: 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.
authors.affiliation: Department of Mechanical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
authors.forename: Marta C
authors.initials: MC
authors.lastname: Hatzell
authors.forename: Muralikrishna
authors.initials: M
authors.lastname: Raju
authors.forename: Valerie J
authors.initials: VJ
authors.lastname: Watson
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Stack
authors.forename: Adri C T
authors.initials: AC
authors.lastname: van Duin
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Logan
mesh_terms: D002244:Carbon / Q000737:chemistry*; D003246:Conservation of Energy Resources; D025802:Electric Capacitance; D011211:Electric Power Supplies; D004566:Electrodes; D006108:Graphite; D006863:Hydrogen-Ion Concentration; D012492:Salts; D012965:Sodium Chloride; D014867:Water / Q000737:chemistry*
chemical_list: D012492:Salts; D014867:Water; D012965:Sodium Chloride; D002244:Carbon; D006108:Graphite