Spectroelectrochemistry One . Infrared spectroelectrochemistry Two . Raman spectroelectrochemistry Zeng Yinm Wang

Outline - Introduction -Experimental -Application -Summary and Conclusion

One . Infrared spectroelectrochemistry

- Introduction Infrared spectroscopy has been important for supporting investingations in electrochemistry. It has been used to detect molecules at or near electrode surfaces to aid the study of electrocatalytic reactions,double- layer structure, adsorption ,and related interfacial phenomena.

Experimental ☆ Sampling methods ： External reflection Figure 1. An external reflection arrangement for IR spectroelectrochemistry.

☆ Attenuated total internal reflection Fiqure 3. Electrochemical cell for in situ ATR IR measurements. A top view of the patterrned working electrode-internal reflection element (IRE) is shown at the bottom.

☆ Thin-layer electrochemical cells for in situ infrared measurements Figure .4. In situ IR spectra recorded during methanol oxidation at the indicated potentials on platinum electrodes .(a) The reactant solution contained 1.0 M methanol in 0.1 HClO4.The working electrode was polycrystalline platinum. .(b) The reactant solution contained 1.0 M methanol in 0.1 HClO4.The working electrode was single-crystal platinum electrode.

Application ☆ Adsorbed CO ：surface coverage effects Fiqure. Plot of atop CO peak frequencies vs. CO surface coverage for a Pt electrode in 0.1 M HClO4 at 0.0 V (circles) and 0.3 V (triangles) vs.RHE.

☆ Surface-Enhanced IR Absorption (SEIRA) 6-amino-8-purinethiol Adenine Thymidine DNA Replication Analytical Chemistry, Vol. 76, No. 18, September 15, 2004

Analytical Chemistry, Vol. 76, No. 18, September 15, 2004 NH2 bending v(OH) of water v(NH) NH2 bending C-N stretching N-H bending Figure 6. Potential difference SEIRA spectra of a 6-amino-8- purinethiol-modified gold electrode measured in 0.1 M NaClO4 solution without (a) and with 1 mM thymidine (b). Figure 1. Infrared (a) and Raman spectra (b) of 6-amino-8-purinethiol (solid traces) and adenine (6-aminopurine; dotted traces) in the solid state. Analytical Chemistry, Vol. 76, No. 18, September 15, 2004

Analytical Chemistry, Vol. 76, No. 18, September 15, 2004 Without With v (NH2) and ring vibration Figure 7. Peak intensities of the 3470-, 1700-, 1670-, and 1570-cm-1 bands in the potential-dependent spectra measured in 0.1 M NaClO4 solution without (open symbols) and with (closed symbols)1 mM thymidine. Figure 8. Schematic drawing of the potential-dependent reorientation of the 6-amino-8-purinethiol monolayer on gold and hydrogen bonding with thymidine in solution. Analytical Chemistry, Vol. 76, No. 18, September 15, 2004

Summary and Conclusion For applications in electrochemistry ,IR spectroscopy has been applied most often to investigate molecular adsorption and small organic molecule electrocatalytic oxidation reactions.

Two . Raman spectroelectrochemistry

- Introduction The coupling of Raman spectroscopy with electrochemical systems has its origins near three decades ago in 1973 when Fleishmann and co-workers reported Raman spectra f rom Hg2Cl2,Hg2Br2,and HgO electrochemistry grown on a thin Hg electrode supported on a Pt substrate.

☆ Surface-Enhanced Raman Scattering (SERS) HPO42- PO43- v(M-O) v(PO3) v(PO3) v(P-O) Figure 2. Dependence of the SER spectra on Ag electrode potential:(a) solution II (0.1 M NaOH + 0.067 M Na2HPO4); (b) solution III(0.067 M Na2HPO4). Inserts show cyclic voltammograms covering same potential range. Potential sweep rate, 20 mV/s.

☆ SERS through thin film transition metal electrodes on enhancing substrates.

☆ Surface plasmon polariton enhanced Raman spectroscopy(SPPERS). vas(N(CH3)2) v(ring) Figure 2. SPPERS of pNDMA from Ag(lll) film grown on mica with NaF as electrolyte at Vapp1= (a) 0, (b) -0.3, (c) -0.4, and (d) 0 V. The signal is almost unobservable at Vapp1 = -0.4 V and almost completely recovers when the applied voltage is brought back to 0 V.

☆ Surface Raman spectroelectrochemistry without enhancement.

Experimental ☆ Raman spectroelectrochemical cells

Application ☆ Characterization of adsorbed organics on electrode surfaces： 1-methylimidazole on Ag v(CH3) Cl- 1-MeIm Figure 2. SERS spectra as a function of potential for 0.05 M 1-MeIm/0.1 M KCl with normal Raman spectrum of 1.0 M aqueous 1-MeIm or reference for (a) 200-1800 cm-1 and (b) 2600-3400 cm-1 regions. Figure 1. Cyclic voltammetry for (a) 0.05 M 1-MeIm/0.1 M KCl . Sweep rates: (a) (一) 100 mV/s，(- - -) 200 mV/s.

Figure 11. Model for adsorption of 1-MeIm at Ag electrodes as a function of potential.Top and bottom views are shown at 90o with respect to each other .

☆ Characterization of specifically adsorbed ions at electrode surfaces 0.6 -0.7 1.2 1.0 -0.5 Fig. 2 SERS spectra in l(AgÈBr) region for (a) methanol (from top to bottom, rational potentials of 0.6, 0.5, 0.3, 0.1, 0.0, [0.1, [0.3, [0.5 and[0.7 V); (c) propanol (from top to bottom, rational potentials of 1.2, 1.1, 1.0, 0.8, 0.6, 0.4, 0.2, and 0.0 V); (e) pentanol (from top to bottom, rational potentials of 1.0, 0.9, 0.8, 0.7, 0.6, 0.4, 0.2, 0.1, [0.1, [0.3 and [0.5 V) containing 0.4 M LiBr(integration time 60 s).

☆ Characterization of interfacial solvent structure at electrode surfaces v(S=O) vs(CH3) va(CH3) v(Ag-Br) vs(CSC) va(CSC) Figure , SERS spectra at Ag electrodes in 0.2 M LiBr in DMSO

☆ Infrared spectroscopy of in situ scanning tunneling microscopy –characterized metal-adsorbate systems Fiqure. IR spectra of CO adsorbed on platinum single-crystal electrodes. Spectra were recorded with the electrode at 0.1 V vs RHE in CO-saturated 0.1 M HClO4.

☆ Discrimination against solution species with Fourier transfrom electrochemically modulated infrared spectroscopy Fiqure. Step-scan FT-EMIRS spectra of 10 mM ferrocyanide in 1.0 M KCl. (a) Power spectrum and phase spectrum recorded by modulating the potential between the limits of 0.02 and 0.42V at 1 Hz. The electrode had been pretreated by cycling the potential between -0.3 V and + 0.8 V for 1 h to form an adsorbed hexacyanoferrate complex. (b)In- phase spectrum after phase rotation of solution ferricyanide and ferrocyanide bands into the quadrature channel.

☆ Raman systems for spectroelectrochemistry

☆ Characterization of electrochemical interfaces using Raman spectroelectrochemical emerision.

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