Understanding the Evolution of Cobalt‐Based Metal‐Organic Frameworks in Electrocatalysis for the Oxygen Evolution Reaction

Abstract

Metal‐organic frameworks (MOFs) have attracted increasing attention as a promising electrode material for the oxygen evolution reaction (OER). Comprehending catalytic mechanisms in the OER process is of key relevance for the design of efficient catalysts. In this study, two types of Co based MOF with different organic ligands (ZIF‐67 and CoBDC; BDC=1,4‐benzenedicarboxylate) are synthesized as OER electrocatalysts and their electrochemical behavior is studied in alkaline solution. Physical characterization indicates that ZIF‐67, with tetrahedral Co sites, transforms into α‐Co(OH)2 on electrochemical activation, which provides continuous active sites in the following oxidation, whereas CoBDC, with octahedral sites, evolves into β‐Co(OH)2 through hydrolysis, which is inert for the OER. Electrochemical characterization reveals that Co sites coordinated by nitrogen from imidazole ligands (Co−N coordination) are more inclined to electrochemical activation than Co−O sites. The successive exposure and accumulation of real active sites is responsible for the gradual increase in activity of ZIF‐67 in OER. This work not only indicates that CoMOFs are promising OER electrocatalysts but also provides a reference system to understand how metal coordination in MOFs affects the OER process.

Single Metal Atom Catalysts and ORR: H-Bonding, Solvation, and the Elusive Hydroperoxyl Intermediate

“…The Co 2p 3/2 core level line shape is strongly influenced by the reaction (Figure 1b, left), displaying a strong remodulation of the multiplet splitting structure with respect to the pristine sample, showing an intensity decrease of the components at 784.3, 782.1, and 780.1 eV and the growth of new peaks at 781.9, 780.3, and 779.6 eV. In a very recent report on Co-based metalorganic frameworks, 78 the latter component was associated with CoOOH species. The lowest binding energy feature that is evident at 778.2 eV on the "as grown" sample is due to the Gunnarsson and Schonhammer transfer of the screening charge.…”

“…The Co 2p 3/2 core level line shape is strongly influenced by the reaction (Figure b, left), displaying a strong remodulation of the multiplet splitting structure with respect to the pristine sample, showing an intensity decrease of the components at 784.3, 782.1, and 780.1 eV and the growth of new peaks at 781.9, 780.3, and 779.6 eV. In a very recent report on Co-based metalorganic frameworks, the latter component was associated with CoOOH species. The lowest binding energy feature that is evident at 778.2 eV on the “as grown” sample is due to the Gunnarsson and Schonhammer transfer of the screening charge. , The observed quenching of the latter peak upon exposure to the water/oxygen mixture witnesses binding of the ligands to the Co metal site, possibly associated with a change of the metal oxidation state. , From the O 1s and Co 2p 3/2 core level intensities reported in Figure b the complex surface coverage can be estimated.…”

Use of the Advantages of Titanium in the Metal: Organic Framework

“…Based on the inexpensiveness and availability of cobalt salts, cobalt-based MOFs have been widely used in different applications, such as oxygen and hydrogen evolution, catalysis, electrocatalysis, synthesis of nanomaterials, and more [57][58][59]. These structures can provide a transition porous framework and ultra-high surface area for photocatalytic H 2 production.…”

POM@ZIF Derived Mixed Metal Oxide Catalysts for Sustained Electrocatalytic Oxygen Evolution

“…This can result in the conversion of Co 2 + from ZIF-67 to α-Co(OH) 2 and β-Co(OH) 2 , followed by the formation of their corresponding oxidized forms (CoOOH), [21,22] while the original frameworks collapse and lose their porosity. [23,24] As these chemical and structural changes generally lead to low catalytic activity, various conversion routes have been developed to access more robust, more active POM@ZIF derived composites, leading to metal oxides, [25] metal sulfides, [26] metal carbides, [27] and metal phosphides. [28,29] Often, these composites combine increased electrical conductivity with chemical and mechanical stability, making them interesting new OER catalysts.…”