Surface construction of loose Co(OH)₂ shell derived from ZIF-67 nanocube for efficient oxygen evolution

The rational design of nanostructure is very important for improving the number and effective utilization of active sites of the electrocatalysts. Here, a core-shell nanostructure composed of ZIF-67 core and Co(OH)₂ shell (ZIF-67@Co(OH)₂) has been obtained by subjecting ZIF-67 nanocube to the optimal high temperature etching process. After refluxing and etching in ethanol/water mixed solution, the loose Co(OH)₂ shell can be constructed based on the surface of etched ZIF nanocube, which provides the obviously abundant active cobalt sites and better contact for oxygen evolution reaction (OER). Compared to the whole hollow Co(OH)₂ nanocube, the solid ZIF-67 core in ZIF-67@Co(OH)₂ can be favorable for charge transfer and provide the stable structure. The synergistic effect between Co(OH)₂ shell and ZIF-67 core under suitable etching regulation can realize the optimized electrocatalysis for OER. The performance measurements show that Co(OH)₂-1 after refluxing 1 h demonstrates the excellent activity requiring 354 mV overpotential at the current density of 10 mA cm^-2 and the good stability. The enhanced mechanism may be due to the formation of loose Co(OH)₂ as shell with fully exposed active sites, as well as the synergistic effect between ZIF-67 core and Co(OH)₂ shell. Therefore, the surface construction of active composites based on ZIF precursor may be a new strategy for efficient electrocatalysis for water splitting.