A Porphyrinic Zirconium Metal–Organic Framework for Oxygen Reduction Reaction: Tailoring the Spacing between Active-Sites through Chain-Based Inorganic Building Units

Abstract

The oxygen reduction reaction (ORR) is central in carbon-neutral energy devices. While platinum group materials have shown high activities for ORR, their practical uses are hampered by concerns over deactivation, slow kinetics, exorbitant cost, and scarce nature reserve. The low cost yet high tunability of metal–organic frameworks (MOFs) provide a unique platform for tailoring their characteristic properties as new electrocatalysts. Herein, we report a new concept of design and present stable Zr-chain-based MOFs as efficient electrocatalysts for ORR. The strategy is based on using Zr-chains to promote high chemical and redox stability and, more importantly, tailor the immobilization and packing of redox active-sites at a density that is ideal to improve the reaction kinetics. The obtained new electrocatalyst, PCN-226, thereby shows high ORR activity. We further demonstrate PCN-226 as a promising electrode material for practical applications in rechargeable Zn-air batteries, with a high peak power density of 133 mW cm –2 . Being one of the very few electrocatalytic MOFs for ORR, this work provides a new concept by designing chain-based structures to enrich the diversity of efficient electrocatalysts and MOFs.

Metal–Organic‐Framework‐Supported Molecular Electrocatalysis for the Oxygen Reduction Reaction

“…Co porphyrins are active and robust for electrocatalytic ORR, which is a significant process in many new energy conversion technologies, including fuel cells and metal–air batteries [34–41] . Through ligand exchange, [42–45] we can graft Co porphyrins on MOF surfaces (Figure 1 c), considering the following benefits of using MOFs as supports [46–53] . First, with different metals and organic linkers, the compositions of MOFs can be modified to make diverse hybrids.…”

High‐Throughput Electron Diffraction Reveals a Hidden Novel Metal–Organic Framework for Electrocatalysis

“…With the access to almost unlimited combinations of inorganic building units and organic linkers, more than 100,000 different MOFs have been reported over the past two decades [22] . Interestingly, through the control of reaction kinetics or thermodynamics, different structures with distinct properties can be obtained even using the same building units [23][24][25][26] . A relevant example is the large sub-class of MOFs termed zeolitic imidazolate frameworks (ZIFs) [27] , which are synthesized by connecting tetrahedrally-coordinated metal ions and linkers.…”

Metal–Organic‐Framework‐Supported Molecular Electrocatalysis for the Oxygen Reduction Reaction

“…[34][35][36][37][38][39][40][41] Through ligand exchange, [42][43][44][45] we can graft Co porphyrins on MOF surfaces (Figure 1 c), considering the following benefits of using MOFs as supports. [46][47][48][49][50][51][52][53] First, with different metals and organic linkers, the compositions of MOFs can be modified to make diverse hybrids. Second, the shape and size of MOFs can be tuned to optimize electron transfer and mass transportation for electrocatalysis.…”