Fused Hybrid Linkers for Metal–Organic Frameworks-Derived Bifunctional Oxygen Electrocatalysts

Abstract

<div> <div> <div> <p>Preparation of electrocatalysts often relies on the use of multiple starting materials – inorganic salts or organometallic precursors, nanostructured carbon supports, organic additives, dopants and carbonization under modifying atmospheres (e.g. NH<sub>3 </sub>or H<sub>2</sub>) – with the examples of electrocatalysts arising from a single precursor being much less common. Herein, we have surveyed a series of heterobivalent scaffolds to identify an iron/benzimidazole-based metal– organic framework as a uniform starting material. By merging the catechol and imidazole units together, we get direct entry into a highly efficient bifunctional oxygen electrocatalyst, which alleviates the need for additional dopants and modifying conditions (ORR: <i>E</i><sub>on</sub> = 1.01 V, <i>E</i><sub>1/2</sub> = 0.87 V vs. RHE in 0.1 M KOH; OER: 1.60 V @10 mA cm<sup>–2</sup> in 0.1 M KOH; ∆<i>E</i> = 0.73 V). We demonstrate that by fine-tuning the chemical nature of an organic linker, one is able modulate the electrochemical properties of a single precursor-derived electrocatalyst material. </p> </div> </div> </div>

Surveying Iron–Organic Framework TAL-1-Derived Materials in Ligandless Heterogeneous Oxidative Catalytic Transformations of Alkylarenes

“…Moreover, TAL-1-900 can be utilized in metal-catalyzed transformations in a ligand-free manner, as the Fe-N x and other sites with potential catalytic activity (e.g., pyridinic, pyrrolic, or graphitic nitrogens) are preassembled during the carbonization step (Scheme 1d) and subsequently made accessible by acid etching. 11 For instance, the presence and precise distribution of these active sites is known to be essential for the overall performance of the bifunctional electrocatalyst materials in electrochemical OER/ORR reactions. [15][16][17][18] One challenge that we wished to address by using our newly developed materials was the practical, laboratorybench conversion of alkylarenes 19 into the corresponding arylcarboxylic acids or ketones.…”

“…20 In 2007, Nakanishi and Bolm introduced an iron chloride-catalyzed oxidation conducted in pyridine with tert-butyl hydroperoxide (TBHP) as the terminal oxi-dant. 21 Given the fact that our bifunctional ORR/OER electrocatalyst TAL-1-900 and its MOF precursor TAL-1 incorporated ligated iron centers, 11 we wished to investigate their performance in similar transformations.…”

“…The surface of porous TAL-1-900 is covered with catalytically active Fe-N x sites (pyridinic, pyrrolic, and graphitic nitrogen), as shown by X-ray photoelectron spectroscopy. 11 The use of highly organized materials as catalysts can often reduce the need for complimentary ligands and bases, and can ensure that low levels of metal leaching occur, potentially rendering the heterogeneous catalyst material recyclable.…”

“…[6][7][8] We recently showed that, by altering the structure of the underlying fused hybrid carbon-rich organic linkers, 9 one can achieve substantial gains in the electrochemical performance of single-precursor-derived MOF-based electrocatalyst materials in oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs). 10,11 Here, we assess the best-performing electrocatalyst from the ORR/OER series, TAL-1-900, and its precursor TAL-1 (Scheme 1) in various catalytic oxidative transformations. 12 In 1964, Jasinski reported 13 cobalt phthalocyanine as the first ORR electrocatalyst material not based on a platinum-group metal.…”

“…13 In the present work, we intended to take a reciprocal approach by examining the performance of the recently developed electrocatalyst TAL-1-900 and its direct precursor in oxidative reactions. 11 Whereas TAL-1 is a nonporous polycrystalline MOF, TAL-1-900 is a porous material (Scheme 1b and 1c) obtained from TAL-1 by carbonization at 900 °C and subsequent acid leaching. The latter procedure removes iron oxides from the surface of the material and decreases the amount of -Fe in the carbon onion-shell-embedded -Fe/Fe 3 C nanocrystals.…”