Mechanistic study of an immobilized molecular electrocatalyst by in situ gap-plasmon-assisted spectro-electrochemistry

Abstract

Immobilised first-row transition metal complexes are potential low-cost electrocatalysts for selective CO2 conversion to produce renewable fuels. Mechanistic understanding of their function is vital for the development of next-generation catalysts, though poor surface sensitivity of many techniques makes this challenging. Here, a nickel bis(terpyridine) complex is introduced as a CO2 reduction electrocatalyst in a unique electrode geometry, sandwiched by thiol anchoring moieties between two gold surfaces.Gap-plasmon-assisted surface-enhanced Raman scattering spectroscopy coupled with density functional theory calculations reveals the nature of the anchoring group plays a pivotal role in the catalytic mechanism by eliminating ligand loss. Our in-situ spectro-electrochemical measurement enables the detection of as few as 8 molecules undergoing redox transformations in the individual plasmonic hot-spots, together with the calibration of electrical fields via vibrational Stark effects. This advance allows rapid exploration of non-resonant redox reactions at the few-molecule level and provides scope for future mechanistic studies of single-molecules.

Optical suppression of energy barriers in single molecule-metal binding

“…Adatoms were modeled as single gold atoms attached to the molecules. Compared with DFT of molecules bound to large gold layers, DFT from binding to one or two gold atoms matches the experimental SERS well ( 21 , 45 ) at much lower computational cost. Gas-phase geometry optimizations, frequency calculations, and calculations for changes in electron density (Fig.…”

Atomically Smooth Single-Crystalline Platform for Low-Loss Plasmonic Nanocavities

“…By coupling optical fields with collective electronic excitations (i.e., surface plasmons), plasmonic nanoparticles have the ability to confine light down to a deep-subwavelength scale (e.g., 10 nm) and produce enhanced local electromagnetic fields. , However, it is challenging to achieve more tightly confined optical fields (e.g., sub-5 nm) . Recently, nanoparticle-on-mirror (NPoM) plasmonic nanocavities, , formed by placing a metal nanoparticle on a metal film separated with a nanometer-thick dielectric layer, have attracted intensive research interest due to their capability of extreme optical confinement and ease of fabrication. − They have given rise to a series of breakthroughs in state-of-the-art nanophotonic research and applications, − such as spontaneous emission enhancement, ,, strong coupling, ,, optical sensing, ,,, and quantum plasmonics. , Usually, the implementation of NPoM nanocavities uses deposited metal films as the mirror, − ,− ,− which have a polycrystalline structure and a typical surface root-mean-square (RMS) roughness of a few nanometers . Due to the extreme confinement of the optical fields in the nanometer-scale gap, granular polycrystalline metal films can introduce a significant optical loss because of the scattering of electrons by surface roughness and numerous grain boundaries. − This limits th...…”

Water-Wettable Open Plasmonic Nanocavities for Ultrasensitive Molecular Detections in Multiple Phases

“…Because of the strong confinement of the optical field, the coupling between the charge oscillations in a metal nanoparticle and the image charges in a nearby mirror film has attracted considerable attention in numerous applications ranging from metamaterials to photocatalysis to plasmonic sensing. − To date, to create a tiny cavity between the metal nanoparticle and metal film, it is essential to have a spacer layer that separates them in proximity. For example, nonmetal thin layers of either SiO 2 , semiconductors, or self-assembled monolayers are deposited onto a gold film, and thereafter, gold nanoparticles are placed on top of the nonmetal layer. − Alternatively, gold nanoparticles fully coated with either SiO 2 or organic molecules can be introduced onto a gold film. − In either case, the nanocavities are produced as occupied by the spacer layers. Consequently, it is evident that the molecules in surrounding media are unable to diffuse into the nanocavity, where the optical field is significantly enhanced.…”