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.