Facile construction of CoNi-MOF nanosheet arrays and exploration of the active sites for oxygen evolution reaction with ultralow overpotential

Developing efficient and inexpensive electrocatalysts for oxygen evolution reaction (OER) is currently a research hotspot in the field of water splitting for hydrogen production. In this work, a series of oriented CoNix-metal organic frameworks nanosheets (CoNix-MOFs, x = 0.23, 0.48, 0.96) were successfully prepared on carbon fiber paper (CFP) to form the CoNix-MOFs/CFP arrays by a facile construction. Electrochemical test results indicated that the optimized CoNi0.48-MOF/CFP exhibits the ultralow overpotential of 206 mV at a current density of 10 mA cm−2 and low Tafel slope of 37 mV dec−1. Moreover, an in-depth exploration of the active site shows that the actual active species is CoNi-MOF/CoNiOOH composite for OER. The excellent OER performance could be mainly attributed to the formation of low-crystalline CoNiOOH, electronic coupling between Ni and Co metals and the cross-linked nanostructure. This study will be helpful for expanding the sheet structural design of MOF catalysts and provide an example for the exploration of MOF active species.