Carbon-supported and nitrogen-coordinated single iron site materials (denoted as Fe−N−C) are the most promising platinum group metal (PGM)-free cathode catalysts for the oxygen reduction reaction (ORR) because of their encouraging activity and continuously improved stability. However, current Fe−N−C catalysts derived from zeolitic imidazolate framework-8 (ZIF-8) nanocrystal precursors via thermal activation at high temperatures often suffer from low accessible Fe sites because the most active sites are buried within bulk carbon nanoparticles. The morphology limitation significantly mitigates the critical three-phase interfaces for creating effective active sites, which requires sufficient ionomer coverage for conducting protons therefore inhibiting the mass transfer of reactants (i.e., O 2 ) within electrodes in proton-exchange membrane fuel cells. Herein, we report an effective strategy for designing a core−shell composite precursor consisting of a polyhedron N-doped porous carbon core from ZIF-8 and a shell from an Fe(III) tetraphenylporphyrin chloride-based conjugated microporous polymer. The resulting core−shell structured Fe−N−C catalyst contains most of the atomic Fe sites at the shell layer with increased density. The unique catalyst design can shorten the diffusion distance of H + and O 2 and facilitate H 2 O product removal, promoting the promoted ORR in thick PGM-free cathodes. Hence, the membrane electrode assembly with optimal Fe−N−C catalysts achieved encouraging current densities of 32 mA cm −2 at 0.9 V iR-free (1.0 bar O 2 ) and 102 mA cm −2 at 0.8 V (1.0 bar air) and a peak power density of 0.43 W cm −2 (1.0 bar air). This work provides an approach to constructing critical M−N−C catalysts with easily accessible single metal active sites in surface layers for the ORR and other critical electrocatalytic reactions.
Zn-air batteries are a promising source of renewable energy for portable electronic devices and automobiles because of low-cost and high energy density. The efficiency of Zn-air batteries significantly rely on the oxygen reduction reaction in air cathode, development of efficient electrochemical catalysts is kindly important. In the past decade, inspired by graphene, porous carbon nanosheets have been widely developed and studied in the field of energy conversion and storage due to their adjustable structure, good and long-distance conductivity, rich porosity and abundant active sites, as well as excellent performance. In this review, various rational preparation methods towards porous carbon nanosheet-based catalysts are summarized. Then, the catalytic active sites in porous carbon nanosheets are classified, and the relationship between performance and active sites are discussed. At the end of this review, the challenges and future prospects for rational development of two-dimensional porous carbon-based electrochemical oxygen reduction reaction catalysts as air cathode for Zn-air batteries are discussed. This review will give guideline for the development of novel porous carbon-based materials for energy conversion and storage.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.