Nature of the Electrical Double Layer on Suspended Graphene Electrodes

Abstract

The structure of interfacial water near suspended graphene electrodes in contact with aqueous solutions of Na 2 SO 4 , NH 4 Cl, and (NH 4 ) 2 SO 4 has been studied using confocal Raman spectroscopy, sum frequency vibrational spectroscopy, and Kelvin probe force microscopy. SO 4 2− anions were found to preferentially accumulate near the interface at an open circuit potential (OCP), creating an electrical field that orients water molecules below the interface, as revealed by the increased intensity of the O−H stretching peak of H-bonded water. No such increase is observed with NH 4 Cl at the OCP. The intensity of the dangling O−H bond stretching peak however remains largely unchanged. The degree of orientation of the water molecules as well as the electrical double layer strength increased further when positive voltages are applied. Negative voltages on the other hand produced only small changes in the intensity of the H-bonded water peaks but affected the intensity and frequency of dangling O−H bond peaks. The TOC figure is an oversimplified representation of the system in this work.

Direct Probe of Electrochemical Pseudocapacitive pH Jump at a Graphene Electrode**

“…[25,26] The second difficulty can be overcome by using graphene as an electrode; graphene, an atom-thickness metal-like material, can serve as the electrode while allowing the IR light to reach the electrode surface. [16,[27][28][29][30] As such, combining SFG with a graphene electrode allows us to explore the molecularlevel insight into the interfacial conformations under electrified conditions. [16] Here, we perform HD-SFG measurements at the CaF 2supported electrified graphene/water interface.…”

Ion and water adsorption to graphene and graphene oxide surfaces

“…Recently, Yang et al used SFG to probe bilayer graphene floating on dilute salt solutions of Na 2 SO 4 , (NH 4 ) 2 SO 4 , and NH 4 Cl at different applied potentials. 62 Measurements at the open circuit potential showed an increase in SFG intensity in the water region over subphase Na 2 SO 4 (Fig. 6a) and (NH 4 ) 2 SO 4 (Fig.…”

Ca-dimers and solvent layering determine electrochemically active species in Ca(BH$_4$)$_2$ in THF

“…The rich isomer subpopulations with distinct orientations in the IDL make it an excellent playground for interfacially-sensitive, polarization-dependent spectroscopies that can capture these differences. Furthermore, the bias-dependence switch in local population from oriented dimers to monocations should be observable with chemically-sensitive vibrational [32][33][34] and electronic probes. [35][36][37] The required potential differences to enrich the IDL with charged species and, presumably, the disruption and population of the DL with more charged species at even higher potentials, may be consistent with known overpotentials for Ca deposition.…”