Molecular structure at electrode/electrolyte solution interfaces related to electrocatalysis

Abstract

The potential dependence of the interfacial water structure at Pt and Au thin film electrodes was investigated by sum frequency generation (SFG) spectroscopy in internal reflection mode. In the case of the Pt electrode, two broad peaks were observed in the OH stretching region at ca. 3200 cm(-1) and ca. 3400 cm(-1), which are known to be due to the symmetric OH stretching (upsilon1) of tetrahedrally coordinated, i.e., strongly hydrogen bonded "ice-like" water, and the asymmetric OH stretching (upsilon3) of water molecules in a more random arrangement, i.e., weakly hydrogen bonded "liquid-like" water, respectively. In the case of the Au electrode, however, a 3400 cm(-1) band was dominant in the SFG spectrum, suggesting that the interaction between water molecules and Au and Pt are different, i.e., water molecules are more disordered at the Au surface. The potential dependence of interfacial water during the methanol oxidation reaction on a Pt electrode was also investigated. SFG intensity strongly depended on electrode potential. Several possibilities are suggested for the potential dependence of the SFG intensity.

Enhanced Stability of a Carbon Monoxide Monolayer Adsorbed on Platinum under Electrochemical Control Probed by Sum-Frequency Generation Spectroscopy

“…Whatever the environment where they occur (gas, liquid), the monitoring and fundamental understanding of these molecular reactions at the surface of the catalyst require the use of sensitive and selective analytical and spectroscopic tools. [4][5][6][7][8][9][10][11][12][13] Nonlinear Sum-Frequency Generation spectroscopy (SFG) [14][15][16][17][18][19][20][21][22] is a powerful in situ probe of the surface coverage and adsorption geometry in a reactor [23][24][25][26][27][28] , as well as in a spectro-electrochemical cell. In the latter case, the electric potential applied across the surface controls the chemical reaction and the structure of the electrodeelectrolyte interface 29 .…”

Computational Chemistry Applied to Reactions in Electrocatalysis

“…In order to derive experimentally whether the water structure at the water-electrode interface is crystalline or rather disordered, measured vibrational spectra have been analyzed [35], in particular focusing on the OH stretch vibration in the range between 2800 and 3800 cm −1 . Generally, OH stretch vibrations at about 3200 cm −1 have been assigned to three-fold coordinated water, i.e., water in a disordered liquid-like structure, whereas OH stretch vibrations at about 3400 cm −1 have been taken as a signature of four-fold coordinated water, i.e., highly-ordered ice-like water molecules [36].…”

“…Generally, OH stretch vibrations at about 3200 cm −1 have been assigned to three-fold coordinated water, i.e., water in a disordered liquid-like structure, whereas OH stretch vibrations at about 3400 cm −1 have been taken as a signature of four-fold coordinated water, i.e., highly-ordered ice-like water molecules [36]. While for Pt(111) two broad peaks at 3200 cm −1 and 3400 cm −1 were obtained [35], the observed vibrational spectra on Au(111) were dominated by a broad peak around 3500 cm −1 ; however, this peak was attributed to oxide formation. The results were interpreted as being an indication that on Pt(111) ordered and disordered water structures coexist whereas on Au(111) the water is less well-ordered.…”

2 Surface Thermodynamics of Metal/Solution Interface: the Untapped Resources

“…SFG application to various platinum/solution interfaces was recently reviewed. 31 SFG is able to provide a reliable separation of contributions from hydrogen ( Pt-H band), anions and water molecules, 236,237 and already discovered various types of potential-dependent lateral water bonding. Combination of these results and progress of laser pulse experiments can be highly resultive, but today the data of these two techniques are available for platinum surfaces of different structure.…”