Abstract
Spectroscopic detection of reaction intermediates upon a variety of electrode surfaces is of major interest within physical chemistry. A notable technique in the study of the electrochemical interface has been surface-enhanced Raman spectroscopy (SERS). The drawback of SERS is that it is limited to roughened gold and silver substrates. Herein we report that shell-isolated nanoparticles for enhanced Raman spectroscopy (SHINERS) can overcome the limitations of SERS and has followed the oxygen reduction reaction (ORR), within a nonaqueous electrolyte, on glassy carbon, gold, palladium, and platinum disk electrodes. The work presented demonstrates SHINERS for spectroelectrochemical studies for applied and fundamental electrochemistry in aprotic electrolytes, especially for the understanding and development of future metal-oxygen battery applications. In particular, we highlight that with the addition of Li(+), both the electrode surface and solvent influence the ORR mechanism, which opens up the possibility of tailoring surfaces to produce desired reaction pathways.
Highlights
Spectroscopic detection of reaction intermediates upon a variety of electrode surfaces is of major interest within physical chemistry
U nderstanding the electrochemistry of oxygen in nonaqueous electrolyte media is of great interest, in particular, for the development of metal-air batteries,[1,2] where the formulation of a stable electrolyte is a major challenge and so far has inhibited their development.[3−5] The oxygen reduction and oxidation reaction mechanisms can be complex, involving multiple intermediates, and are highly dependent upon the solvent used.[5−7] There have been a number of recent studies on the development of the electrolyte media,[8,9] using a variety of analytical and spectroscopic techniques.[9−12] In particular, surface-enhanced Raman spectroscopy (SERS)[13] has been shown to be a valuable technique; it is limited by the surfaces that it can be used to analyze, essentially gold and silver.[14,15]
SERS is a nondestructive and noninvasive technique; it can be used to investigate the chemical bonding of surface species, making it a valuable technique to study in situ the oxygen reduction and evolution reactions (ORR and OER), taking place at the electrode interface.[18]
Summary
Than 4 nm will drastically reduce the enhancement from the Au core (Figure S1.1). The gold nanoparticle has a strong electromagnetic field that enhances the Raman signal, while the SiO2 shell inhibits any catalytic effect from the gold core.[23]. Thereby, there is an absence of a metal−O2− interaction (area indicated via a #), and this indicates that the SHINERS particles are pinhole-free (Figures S1.1−S1.4) This provides strong verification that the O2− peak (υO−O) at ∼1110 cm−1 originates solely from its interaction at the GC surface, not with the gold core of the SHIN, with it being detected solely due to the Raman enhancement from the SHIN particles. SHIN preparation, synthesis and validation, transfer onto electrode surfaces and enhancement factor of SHIN particles, supporting electrochemical data, Raman spectra of materials used, Raman peak analysis comparison of superoxide on metal surfaces, and SERS and SHINERS experiments under argon deoxygenated electrolytes. SHIN preparation, synthesis and validation, transfer onto electrode surfaces and enhancement factor of SHIN particles, supporting electrochemical data, Raman spectra of materials used, Raman peak analysis comparison of superoxide on metal surfaces, and SERS and SHINERS experiments under argon deoxygenated electrolytes. (PDF)
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