title: Speciation of Adsorbed Phosphate at Gold Electrodes: A Combined Surface-Enhanced Infrared Absorption Spectroscopy and DFT Study.
abstract: Despite the significance of phosphate buffer solutions in (bio)electrochemistry, detailed adsorption properties of phosphate anions at metal surfaces remain poorly understood. Herein, phosphate adsorption at quasi-Au(111) surfaces prepared by a chemical deposition technique has been systematically investigated over a wide range of pH by surface-enhanced infrared absorption spectroscopy in the ATR configuration (ATR-SEIRAS). Two different pH-dependent states of adsorbed phosphate are spectroscopically detected. Together with DFT calculations, the present study reveals that pKa for adsorbed phosphate species at the interface is much lower than that for phosphate species in the bulk solution; the dominant phosphate anion, H2PO4(-) at 2 < pH < 7 or HPO4(2-) at 7 < pH < 12, undergoes deprotonation upon adsorption and transforms into the adsorbed HPO4 or PO4, respectively. This study leads to a conclusion different than earlier spectroscopic studies have reached, highlighting the capability of the ATR-SEIRAS technique at electrified metal-solution interfaces.
authors.affiliation: Institute for Catalysis, Hokkaido University , Sapporo 001-0021, Japan.|Graduate School of Environmental Science, Hokkaido University , Sapporo 060-0810, Japan.
authors.forename: Momo
authors.initials: M
authors.lastname: Yaguchi
authors.affiliation: Center for Energy and Environmental Science, Shinshu University , Nagano 390-8621, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Uchida
authors.affiliation: Institute for Catalysis, Hokkaido University , Sapporo 001-0021, Japan.
authors.forename: Kenta
authors.initials: K
authors.lastname: Motobayashi
authors.affiliation: Institute for Catalysis, Hokkaido University , Sapporo 001-0021, Japan.
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Osawa