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

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.