A Tunable Amorphous Heteronuclear Iron and Cobalt Imidazolate Framework Analogue for Efficient Oxygen Evolution Reactions

Abstract

The structural diversity and tunable functionality of the amorphous metal-organic frameworks (aMOFs) highlights this class of materials as a promising candidate for the development of sustainable energy technologies. The electrocatalytic performance in oxygen evolution reaction (OER) can be greatly improved by incorporating the hetero-metallics into MOFs. Herein, the OER performance was significantly improved by the incorporation of Fe 3 + ions into the crystalline cobalt-based MOF, leading to amorphous structure. Benefiting from the optimized surface morphology and electrochemical surface area, charge transport, was greatly facilitated. The Fe/Co aMOF with 1/4 ratio (labeled as AFC-MOFs (1 : 4)) exhibited an excellent and stable OER activity, with an ultralow overpotential (256 mV at 10 mA cm À 2) and Tafel slope of 42.7 mV dec À 1. XAS found that the majority of Co 2 + in AFC-MOFs (1 : 4) is converted to low-spin Co 3 + upon OER, while Fe 3 + is maintained during the OER process, supporting the synergistic catalytic mechanism between Fe and Co. This material outperforms benchmark IrO 2 , which could be attributed to the hollow amorphous structure and the optimized electronic properties.

Electrocatalyst with Dynamic Formation of the Dual-Active Site from the Dual Pathway Observed by In Situ Raman Spectroscopy

“…Exploring the dynamic structural reconstruction of a catalyst relies on in situ techniques, such as X-ray absorption spectroscopy (XAS), , X-ray diffraction analysis (XRD), and optical spectroscopy, to directly observe active species. Notably, Raman spectroscopy as a powerful surface characterization method enables the crystal phase, chemical states, and structural distortion to be examined, and has been widely used under in situ and operando electrochemical conditions. ,− …”

Hydrogen Evolving Activity of Dithiolene-Based Metal–Organic Frameworks with Mixed Cobalt and Iron Centers

“…The hybrid nature of MOFs allows for a high degree of variability and multivariate synthetic tunability. Such tunability has been explicitly studied by Yaghi and co-workers, where MOFs were shown to incorporate up to 8 unique ligands and 10 different metals without disturbing the crystalline structure of the overall framework. , In the context of electrocatalysis, introducing multiple metal centers into the same structure is a common strategy to improve catalytic performance. − For example, it is well-known that the incorporation of Fe into Co or Ni (oxy)­hydroxides can dramatically improve the OER performance of the catalysts. , Chang and co-workers also reported the synthesis of the multivariate Co/Cu COF-367 for CO 2 reduction. The incorporation of Cu allowed for dilution of the active Co sites and substantially enhanced activity on a per-cobalt basis .…”