Synthesis and operando EC-STM investigation of NHC-based surface metal–organic frameworks for electrocatalysis in aqueous KHCO3 solution

This thesis focused on the synthesis, characterization, and electrocatalytic behaviour of surface metal–organic frameworks (SMOFs) composed of N-heterocyclic carbene (NHC) linkers and gold nodes. A scalable liquid-phase approach was employed using biscarbene and triscarbene precursors capable of generating two and three carbene centres, respectively. The synthesis of one-dimensional (1D) SMOFs from the biscarbene precursor was straightforward, whereas the formation of two-dimensional (2D) SMOFs required the combined use of both precursors. The resulting materials were characterized by X-ray photoelectron spectroscopy (XPS) and electrochemical scanning tunnelling microscopy (EC-STM). The latter was instrumental in revealing potential-dependent surface dynamics at the atomic scale. In Ar-saturated aqueous KHCO₃ electrolyte, EC-STM revealed enhanced molecular-chain mobility and the formation of gold ad-islands during cathodic sweeps. The highest activity towards the hydrogen evolution reaction (HER) was observed for the 1D-SMOFs, possibly reflecting their higher surface coverage and greater density of gold sites compared with the more open 2D-SMOF networks. In CO₂-saturated electrolyte, all investigated structures exhibited cathodic current onsets at more positive potentials than those measured in Ar-saturated electrolyte, a promising result for future applications in the carbon dioxide reduction reaction (CO₂RR). Under both Ar and CO₂ saturation, the functionalized surfaces exhibited lower Tafel slopes than bare Au(111), consistent with faster apparent reaction kinetics. These findings highlight the relationship between framework architecture, potential-dependent surface dynamics, and electrocatalytic performance, providing a basis for the design of adaptive NHC-based catalytic interfaces for HER and CO₂RR.