Surface spectroscopy of Pt(1 1 1) single-crystal electrolyte interfaces with broadband sum-frequency generation

Recent advances in vibrational broadband sum-frequency generation (SFG) have allowed us to address electrochemical adsorption and electrocatalytic reactions in unprecedented detail. SFG, as an inherently surface-specific technique, provides a direct observation of only those molecular species that are adsorbed to single crystalline or polycrystalline electrodes without spectral interference from molecular species in the bulk electrolyte. Our data thus offer unique insights into the chemical identity of surface-adsorbed intermediates on single crystals. In this article we will review recent developments in the field of spectro-electrochemistry with sum-frequency generation (SFG) and discuss adsorption of (bi)sulfate as a model system for broadband SFG. Advancing SFG for in situ studies of anion specific adsorption has provided the basis for further studies on formic acid oxidation. Here, rapid acquisitions of broadband SFG spectra synchronized with voltammetric scans have allowed us to perform the first SFG study on the formation of surface adsorbed formate HCOO∗ on a well-ordered Pt(1 1 1) single crystal. Our information from broadband SFG may provide useful information on possible reaction mechanism of formic acid oxidation on Pt(1 1 1) and thus for future theoretical investigations of this intriguing interface.