MOFs-derived 3D hierarchical CoFe2O4/RuO2 hollow nanosheet array for efficient overall water splitting

Accelerating hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) kinetics process is crucial to the development of transition metal oxide based materials as bifunctional catalysts for overall water splitting. Herein, a heterostructured CoFe2O4/RuO2 hollow hierarchical nanosheet array (FeRu-CoOx) has been designed by using MOF as template followed by simultaneous etching-doping process combined with calcination for enhanced HER performance without compromise of OER activity. The MOF-derived FeRu-CoOx exhibits an enhancement on HER performance with 58 mV overpotential to achieve 10 mA cm-2 and a small Tafel slop of 73.1 mV dec-1 in the alkaline solution, compared to CoFe2O4 counterpart (Fe-CoOx) using monometallic Fe etching and doping. In addition, the FeRu-CoOx electrode also shows good OER activity (10 mA cm-2 at an overpotential of 229 mV), better than those of Fe-CoOx (239 mV) and commercial RuO2 electrodes (270 mV). The introduction of Ru helps the construction of heterostructure, which is in favor of exposure of active sites, increasing the electron interaction between different composites, and accelerating charge transfer. The alkali electrolyzer using FeRu-CoOx as cathode and anode shows a small cell voltage with only 1.48 V at 10 mA cm-2 and good tolerance toward long-term stability. The MOF template combined with etching-doping strategy to construct hierarchical and heterostructured materials gives a way to develop advanced bifunctional electrocatalysts for water splitting.