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

Herein, a stable metal-azolate framework with cyclic trinickel(II) clusters, namely [Ni-3(mu(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 mu(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 mu(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.

Automated summary

A stable metal-azolate framework with cyclic trinickel(II) clusters achieved a high current density of 50 mA cm(-2) at a cell voltage of 1.8V in a 1.0 M KOH solution. The framework showed no obvious degradation over 12 hours of continuous operation at a large current density. Theoretical calculations revealed that the unique structure of the framework facilitated the dissociation of H2O molecules and provided a low-energy coupling pathway for water oxidation, resulting in high performance for overall water splitting.