One-dimensional nickel(<scp>ii</scp>) coordination polymers of 9-anthracenyl-4′-benzoate and bispyridyl linkers as efficient electrocatalysts for hydrogen and oxygen evolution reactions

Developing stable, efficient, and affordable Earth-abundant transition metal-based electrocatalysts for water splitting applications is key to producing green hydrogen. This study reports the development of new Ni(II)-based one-dimensional coordination polymers (CPs), namely, [Ni(9-AnBz)₂(4,4'-bpy)₂(MeOH)₂] (CP 1), [Ni(9-AnBz)₂(4,4'-bpe)₂(MeOH)₂] (CP 2), and [Ni(9-AnBz)₂(3,3'-bpdb)₂(H₂O)₂]·H₂O (CP 3) (where 9-AnBz = 9-anthracenyl-4'-benzoate, 4,4'-bpy = 4,4'-bipyridine, 4,4'-bpe = <i>trans</i>-1,2-bis(4'-pyridyl)ethene, and 3,3'-bpdb = 1,4-bis(3'-pyridyl)-2,3-diaza-1,3-butadiene), as novel electrocatalysts. Their structures have been confirmed by single crystal X-ray diffraction. These Ni(II)-based CPs exhibited improved electrocatalytic activity towards both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in 1.0 M KOH. The CP 1 catalyst was found to deliver a low HER onset potential (∼-0.04 V <i>vs.</i> RHE), a small HER overpotential (∼87 mV at -10 mA cm^-2), a Tafel slope of ∼107.0 mV dec^-1, high current density (-496 mA cm^-2 at ∼1.83 V <i>vs.</i> RHE), and high mass activity (∼50.0 A g^-1), comparable to those of commercial Pt/C. Moreover, the CP 1 catalyst also exhibited the best OER activity, with a small overpotential (∼370 mV at 10 mA cm^-2) and a low Tafel slope (∼82 mV dec^-1), showing efficient performance and great promise in hydrogen production systems.