Determination of adsorbed species of hypophosphite electrooxidation on Ni electrode by in situ infrared with shell-isolated nanoparticle-enhanced Raman spectroscopy

Electrooxidation of hypophosphite (H2PO2-) on Ni electrode was investigated at the molecular level by external-reflection Fourier-transform infrared spectroscopy (FTIR), surface-enhanced infrared absorption spectroscopy with attenuated total reflection (ATR-SEIRAS), and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). The results of external-reflection FTIR demonstrated that H2PO2- could be oxidized to HPO32- at significantly low potentials (E < -1.0 V vs. SCE). ATR-SEIRAS result showed that H2PO2ad- could be adsorbed onto the Ni surface via O atoms. The adsorption orientation was further examined using SHINERS, and Ni-O stretching bands of metal-adsorbate vibration were directly detected. Comparative results of SHINERS and those obtained from the density functional theoretical calculation confirmed the adsorption orientation of H2PO2-. The present investigation verified for the first time the adsorption mechanism of H2PO2- electrooxidation on Ni surface through in situ spectroscopic data. (C) 2014 Elsevier B.V. All rights reserved.