Development of Highly Stable Shell-Isolated Nanoparticles for In-situ Electrochemical Raman Studies

Abstract

Understanding electrocatalytic reactions at solid-liquid interfaces requires in situ Raman spectroscopy capable of monitoring transient intermediates and surface reconstruction under operating conditions. However, reliable Raman probing requires shell-isolated plasmonic nanoparticles that provide strong electromagnetic enhancement while preventing direct chemical or electrical interference with the catalyst surface. Hexagonal boron nitride （hBN） is an attractive dielectric shell material because of its atomic scale thickness, chemical inertness, impermeability, and stability under harsh electrochemical conditions. However, conventional high-temperature hBN growth can induce thermal melting and morphological deformation of AuNPs, reducing plasmonic enhancement. To overcome this limitation, this study employed a low temperature plasma-enhanced CVD strategy to form hBN shells while preserving nanoparticle morphology. Au nanocubes （AuNCs） were selected as anisotropic plasmonic cores because their sharp edges and corners generate intense electromagnetic hotspots through the lightning-rod effect. TEM, EDS, Raman, pinhole tests, dark-field imaging, and FDTD simulations confirmed that the AuNC@hBN architecture provides structural stability, chemical isolation, and strong field enhancement. In addition, in situ electrochemical Raman spectroscopy was performed to investigate HER and OER mechanisms, revealing the role of the NiO/Ni interface in HER and potential-induced surface reconstruction in NiFe-LDH and IrOx during OER. This study demonstrates the importance of stable shell-isolated nanostructures and in situ Raman spectroscopy for understanding electrocatalytic interfaces.