Abstract
Electrochemical (EC) and photoelectrochemical (PEC) water splitting represent promising strategies for renewable energy conversion and fuel production and require design of efficient catalysts for the oxygen evolution reaction (OER). Herein, we report the synthesis of two-dimensional (2D) Co-based metal organic framework (Co-MOF) nanosheets and their bifunctional catalytic properties for both EC and PEC OER. Benefiting from the large surface area and abundant isolated metal active sites, the Co-MOF nanosheets exhibited excellent OER activity and stability. The efficient electron–hole generation and separation of the nanosheets, owing to dimensional confinement, contributed to an improved visible light response in PEC OER. This study presents a new strategy to design EC/PEC bifunctional catalyst utilizing unique structural and electronic features of 2D MOF.
Highlights
Electrochemical (EC) and photoelectrochemical (PEC) water splitting are recognized as two attractive processes for clean fuel hydrogen (H2) generation via the conversion of renewable electrical energy into chemical energy and have aroused intense research interest in recent years (Fujishima and Honda, 1972; Zhong and Gamelin, 2010; Kim and Choi, 2014; Zhang et al, 2020)
The obtained bulk MOF-71 was comprised of closely stacking layers (Supplementary Figure 2), which was verified by transmission electron microscopy (TEM) characterizations and suggested the exfoliation mechanism for the nanosheet formation
The nanosheet thickness was limited to a few nanometers based on atomic force microscopy (AFM) measurements (Figure 1C), in consistence with the TEM results
Summary
Electrochemical (EC) and photoelectrochemical (PEC) water splitting are recognized as two attractive processes for clean fuel hydrogen (H2) generation via the conversion of renewable electrical energy into chemical energy and have aroused intense research interest in recent years (Fujishima and Honda, 1972; Zhong and Gamelin, 2010; Kim and Choi, 2014; Zhang et al, 2020). Efficient catalysts that work for both EC and PEC OER are required to allow the seamless operation of water splitting in the presence and absence of sunlight, maximizing the process efficiency Such bifunctional catalyst development mainly resides in metal oxide nanomaterials, such as bismuth vanadate (BiVO4) (Kim and Choi, 2014), hematite (α-Fe2O3) (Zhong and Gamelin, 2010), and tungsten trioxide (WO3) (Sarnowska et al, 2016), most of which, still cannot achieve desirable properties for the two processes simultaneously. The Co-MOF nanosheets were obtained through the exfoliation treatment of premade MOF71 bulk materials, with consecutive processes of hydrothermal reaction in water and sonication in isopropanol. The catalyst ink was prepared by dispersing 2 mg of catalyst powders [bulk MOF-71, Co-MOF nanosheets or Co(OH) nanosheets] in isopropanol (990 μl) and Nafion ionomer (10 μl) (Visopropanol/Vnafion = 99:1) and sonicating for 30 min. The RDE would rotate at speed of 1,600 rpm during our measurement
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