Molecular Engineering of Electrocatalytic Nanomaterials for Hydrogen Evolution: The Impact of Structural and Electronic Modifications of Anchoring Linkers on Electrocatalysis

The anticipated shortage of an increasing number of critical elements, especially metals, requires a shift toward molecularly defined materials with low metal loadings. More particularly, surface-anchored molecular catalysts are attractive to prospectively enable cost-effective electrochemical hydrogen evolution. However, the design of ligands integrating specific anchoring unit(s) for the immobilization of molecular catalysts can be challenging and has direct consequences for the intrinsic properties of the grafted complex. In this work, two cobalt tetraazamacrocyclic complexes bearing pyrene anchoring groups at different positions on the macrocyclic ligands were synthesized. The pyrene unit allows for simple immobilization and electrochemical characterization of the two complexes on multi-walled carbon nanotube-based electrodes. Thorough electrochemical and electrocatalytic investigation demonstrates important differences between the two closely related catalysts in terms of catalyst loading, catalytic response, and stability over time, with a significantly higher stability observed at pH 7 than at pH 2.