Deciphering of advantageous electrocatalytic water oxidation behavior of metal-organic framework in alkaline media

Carboxylic acid-based metal-organic frameworks (MOFs) are normally passed for the pre-catalysts for oxygen evolution reaction (OER) due to the hydroxides constructed in-situ during its alkaline hydrolysis process (AHP) in lye. Whereas, it remains a mystery that they show advantageous activity over prototypical hydroxides when they are directly acted as OER catalysts. Herein, we propose for the first time that the steric hindrance effect of Nafion can induce enhanced catalytic activity of such MOFs. Different from conventional catalysts without AHP, the Nafion with 3D structure weakens the AHP of Co-MOF nanoribbons, thus forming small size and low crystallinity species (cobalt hydroxide) with more active sites. And the existence of Nafion also optimizes its electronic structure, which is confirmed by transmission electron microscopy (TEM), in-situ UV absorption spectra, in-situ Raman spectroscopy and so on. Compared with Co-MOF-K obtained by directly immersing the Co-MOF nanoribbons in 1.0 M KOH, the Co-MOF-NK obtained by AHP of Co-MOF mixed with Nafion shows better catalytic activity. Based on the above inspiration, we realized the low overpotential of 268 mV at 10 mA.cm(-2) by preparing CoFe-MOF-NK. This work provides a new understanding of the structural reconstruction of MOFs in the field of electrocatalysis.

Automated summary

This study proposes for the first time that the steric hindrance effect of Nafion can induce enhanced catalytic activity of carboxylic acid-based metal-organic frameworks (MOFs), forming more active sites by weakening the alkaline hydrolysis process. The use of Nafion optimizes the electronic structure of MOFs, leading to improved catalytic activity.