Spectroelectrochemical Measurement Method of In Situ Surface-Enhanced Raman Spectroscopy for Various Electrode Materials Using a Transmission-Type Plasmonic Sensor

A versatile spectroelectrochemical measurement method of surface-enhanced Raman scattering spectroscopy is developed, and its capability is assessed in an actual electrochemical system. The spectroelectrochemical cell consists of a plasmonic sensor with metal nanoparticles and a wire-type working electrode. The advantages of this method over conventional surface-enhanced Raman scattering methods are as follows: 1) surface-enhanced Raman scattering for electrode materials that show little plasmon resonance; and 2) measurement without undesirable influences on the physical and chemical states of the electrode surface and transport phenomena of reaction species. During the measurement, the sensor contacts the working electrode wire at a single point, allowing the surface-enhanced Raman scattering signal to be obtained from the interfacial area of the working electrode surface without significantly disturbing the mass transfer of the reaction species. As plasmon-active metal nanoparticles are modified on the sensor surface in advance, destructive and complicated pretreatment processes on the working electrode are not required. The method is applied to the in situ analysis of electrolyte decomposition reactions in a Li metal battery to reveal the potential of each decomposition product of an organic solvent containing Li. The obtained surface-enhanced Raman scattering spectrum corresponding to the voltammogram reveals the pathway for obtaining decomposition products, such as Li₂CO₃. In particular, Li₂C₂ was clearly detected with our setup. It is also revealed from the setup that the Ni electrode surface, in contrast to the Cu, does not hold a stable Li-containing composite layer. Such in situ chemical information will contribute to the effective interfacial design of high-performance batteries.