fig1

Figure 1. Imbedded interface-the electrical double layer. (A) schematic of the classical Gouy-Chapman-Stern model. The IHP, OHP and diffuse layer are indicated. The potential φ is shown with respect to the distance from the surface. The yellow and purple denote the cations and anions, respectively; (B) schematic of the modulation setup consisting of piezo-actuated chopped incoming X-ray and lock-in amplifier to extract neat TEY XAS signal under electrical bias; (C) the bias-dependent TEY O K-edge NEXAFS spectra of water collected at the Au electrode. The intensified pre-edge peaks at around 535 eV under negative bias (-20, -60 mV vs. Ag) fingerprint the SD orientation of water molecules (single donor parallel and perpendicular toward the gold surface), namely the dangling hydrogen bonds. These figures are quoted with permission from Velasco-Velez et al.^[7]; (D) schematic of the “dip and pull” setup for ambient pressure XPS measurements. WE, RE, and CE correspond to the working electrode, reference electrode, and counter electrode, respectively; (E and F) normalized bias-dependent N 1s and O 1s core-level peaks collected in KOH aqueous solution containing a spectator molecule pyrazine; (G) double-layer capacitance as a function of applied potential; (H) spectral broadening of liquid phase LPPY N 1s and LPW O 1s components as a function of applied potential. The pzfc of +160 mV, +141 mV extracted from the minimum of indicated N 1s, O 1s V-shaped plots aligns well with that (+123 mV) of a double-layer capacitance method. This figure is quoted with permission from Favaro et al.^[12]. IHP: Inner Helmholtz plane; OHP: outer Helmholtz plane; XAS: X-ray absorption; TEY: total electron yield; XPS: X-ray photoemission spectroscopy; NEXAFS: near-edge X-ray absorption fine structure.