Cyclic Trinickel(II) Clusters in a Metal‐Azolate Framework for Efficient Overall Water Splitting

A cyclic trinickel(II) cluster-based metal-azolate framework is reported as a high-performance bifunctional catalyst for overall water splitting.

Abstract

Herein, a stable metal-azolate framework with cyclic trinickel(II) clusters, namely [Ni₃(μ ₃-O)(BTPP)(OH)(H₂O)₂] (Ni-BTPP, H₃BTPP=1,3,5-tris((1H-pyrazol-4-yl)phenylene)benzene), achieved a current density of 50 mA cm⁻² at a cell voltage of 1.8 V in 1.0 M KOH solution, while the current density of 20%Pt/C@NF||IrO₂@NF is just 35.8 mA cm⁻² at 2.0 V under the same condition. Moreover, no obvious degradation was observed over 12 hours of continuous operation at a large current density of 50 mA cm⁻². Theoretical calculations revealed that the μ ₃-O atom in the cyclic trinickel(II) cluster serves as hydrogen-bonding acceptor to facilitate the dissociation of a H₂O molecule adsorbed on the adjacent Ni(II) ion, giving a lower energy barrier of H₂O dissociation compared with Pt/C; meanwhile, the μ ₃-O atom can also participate in the water oxidation reaction to couple with the adjacent *OH adsorbed on Ni(II) ion, providing a low-energy coupling pathway, thus Ni-BTPP achieves a high performance for overall water splitting.

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