Nickel-Based Water-Soluble Metallopolymer for the Electrochemical Hydrogen Evolution Reaction in Neutral-pH Water

Electrochemical
production of the energy-dense hydrogen molecule
in green solvents such as water, under mild conditions, has been desirable
but challenging. A burgeoning family of catalysts that currently serve
in such hydrogen evolution reactions (HERs) are artificial metalloenzymes
and metallopolymers, which were manifested through the direct syntheses
between HER-active metal complexes and protein matrices or water-soluble
polymers. The direct synthetic method often poses some limitations
on active site variants and synthetic feasibility. Here, we propose
the first HER-active metallopolymer catalyst manifested through the
bottom-up synthetic strategy and a facile postpolymerization modification.
With the advent of this method, the tridentate ligation (N-[2-(aminopropylthio)­phenyl]-2-pyridinemethamine (NNS-PrNH2)) and the water-solubilizing (amino-containing poly­(ethylene glycol)
(PEG-NH2)) pendent units were furnished onto polymer backbone
with quantitative precision. The readily synthesized polymers were
self-folding in water, and subsequently formed the polymeric nanoassemblies
upon nickel-coordination complexation to give a high concentration
of active sites in hydrophobic compartments. The stable metallopolymers
showed practical usage in the electrochemical HER in a pH 7 aqueous
solution, under ambient conditions, resulting in 41 ± 9 μmol
of H2 evolved in 1 h with the satisfactory faradaic efficiencies
of 58 ± 2%.