Structural transformation of metal–organic framework with constructed tetravalent nickel sites for efficient water oxidation

Structural transformation of a bimetallic MOF enables the construction of nickel (oxy)hydroxide with Fe incorporation, where the critical role of Fe is evidenced to promote the formation of tetravalent nickel sites and in turn directly correlates with an enhanced OER activity. A mixture of Ni and Fe oxides is among the most commonly active catalysts for the oxygen evolution reaction (OER) during the water oxidation process. In particular, Ni oxide incorporated with even a small amount of Fe leads to substantively enhanced OER activity. However, the critical role of Fe species during the electrocatalytic process is still under evaluation. Herein, we report nickel (oxy)hydroxide incorporated with Fe through the surface reconstruction of a bimetallic metal-organic framework (NiFe-MOF) during the water oxidation process. The spectroscopic investigations with theoretical calculations reveal the critical role of Fe in promoting the formation of highly oxidized Ni 4+ , which directly correlates with an enhanced OER activity. Both the geometric and electronic structures of the as-reconstructed Ni 1 − x Fe x OOH electrocatalysts can be delicately tuned by the Ni-Fe ratio of the bimetallic NiFe-MOF, further affecting the catalytic activity. As a result, the Ni 1− x Fe x OOH derived from Ni 0.9 Fe 0.1 -MOF delivers low overpotentials of 260 mV at 10 mA cm −2 and 400 mV at 300 mA cm −2 .