Abstract
The development of catalysts with enhanced activity for the oxygen evolution reaction (OER) compared to the traditionally used metal oxide catalysts is crucial for further commercialization of electrolyzers. Because of their high surface area and adjustable pore structure, metal-organic framework (MOF)-based catalysts represent a promising alternative. During the OER in alkaline media, the initial MOF structure is susceptible to transformations including the decomposition of the organic backbone and/or the formation of oxide, hydroxide and oxyhydroxide intermediates. Hence, operando characterizations of MOF catalysts during OER are essential to understand the material's progressive changes and extract the OER catalytic mechanism. This article discusses existing operando X-ray absorption spectroscopy studies of MOF(-derived) catalysts during OER and extracts important parameters for future research regarding operando X-ray absorption spectroscopy characterizations of MOFs during alkaline electrolysis.
Highlights
Because of the increased focus on renewable energy sources, often intermittent by nature, efficient energy conversion and storage systems become more important [1]
This study shows how the operando methods can lead to an increased understanding of the electronic and local structural transformations in metal-organic framework (MOF) materials, which appears to be crucial for high oxygen evolution reaction (OER) activity
In summary, MOF catalysts are affected by chemical transformations that lead to high OER activity
Summary
Because of the increased focus on renewable energy sources, often intermittent by nature, efficient energy conversion and storage systems become more important [1]. A similar influence of the Ni/Fe ratio on the NiFe-MOF-74 OER activity and a similar two-stage transition under OER conditions, including the reversibility of the structural transformation, were observed [35] This is of special interest as it is in contrast to findings regarding the influence of Fe incorporation into Ni oxides, where Fe stabilized the Ni2þ state and inhibited oxyhydroxide formation on Ni [36]. This contradiction underlines the importance of operando analysis of MOF(-derived) structures to study phase transformations during OER in order to extract important mechanisms determining their OER activity.
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