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Nanocasting SiO₂ into metal-organic frameworks imparts dual protection to high-loading Fe single-atom electrocatalysts.

ABSTRACT: Single-atom catalysts (SACs) have sparked broad interest recently while the low metal loading poses a big challenge for further applications. Herein, a dual protection strategy has been developed to give high-content SACs by nanocasting SiO₂ into porphyrinic metal-organic frameworks (MOFs). The pyrolysis of SiO₂@MOF composite affords single-atom Fe implanted N-doped porous carbon (Fe_SA-N-C) with high Fe loading (3.46?wt%). The spatial isolation of Fe atoms centered in porphyrin linkers of MOF sets the first protective barrier to inhibit the Fe agglomeration during pyrolysis. The SiO₂ in MOF provides additional protection by creating thermally stable FeN₄/SiO₂ interfaces. Thanks to the high-density Fe_SA sites, Fe_SA-N-C demonstrates excellent oxygen reduction performance in both alkaline and acidic medias. Meanwhile, Fe_SA-N-C also exhibits encouraging performance in proton exchange membrane fuel cell, demonstrating great potential for practical application. More far-reaching, this work grants a general synthetic methodology toward high-content SACs (such as Fe_SA, Co_SA, Ni_SA).

SUBMITTER: Jiao L

PROVIDER: S-EPMC7275045 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Nanocasting SiO2 into metal-organic frameworks imparts dual protection to high-loading Fe single-atom electrocatalysts.

Jiao Long L Zhang Rui R Wan Gang G Yang Weijie W Wan Xin X Zhou Hua H Shui Jianglan J Yu Shu-Hong SH Jiang Hai-Long HL

Nature communications 20200605 1

Single-atom catalysts (SACs) have sparked broad interest recently while the low metal loading poses a big challenge for further applications. Herein, a dual protection strategy has been developed to give high-content SACs by nanocasting SiO2 into porphyrinic metal-organic frameworks (MOFs). The pyrolysis of SiO2@MOF composite affords single-atom Fe implanted N-doped porous carbon (FeSA-N-C) with high Fe loading (3.46 wt%). The spatial isolation of Fe atoms center ...[more]

PMID: 32504040

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Project description:Metal-organic frameworks (MOFs) have been investigated with regard to the oxygen evolution reaction (OER) due to their structure diversity, high specific surface area, adjustable pore size, and abundant active sites. However, the poor conductivity of most MOFs restricts this application. Herein, through a facile one-step solvothermal method, the Ni-based pillared metal-organic framework [Ni2(BDC)2DABCO] (BDC = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane), its bimetallic nickel-iron form [Ni(Fe)(BDC)2DABCO], and their modified Ketjenblack (mKB) composites were synthesized and tested toward OER in an alkaline medium (KOH 1 mol L-1). A synergistic effect of the bimetallic nickel-iron MOF and the conductive mKB additive enhanced the catalytic activity of the MOF/mKB composites. All MOF/mKB composite samples (7, 14, 22, and 34 wt.% mKB) indicated much higher OER performances than the MOFs and mKB alone. The Ni-MOF/mKB14 composite (14 wt.% of mKB) demonstrated an overpotential of 294 mV at a current density of 10 mA cm-2 and a Tafel slope of 32 mV dec-1, which is comparable with commercial RuO2, commonly used as a benchmark material for OER. The catalytic performance of Ni(Fe)MOF/mKB14 (0.57 wt.% Fe) was further improved to an overpotential of 279 mV at a current density of 10 mA cm-2. The low Tafel slope of 25 mV dec-1 as well as a low reaction resistance due to the electrochemical impedance spectroscopy (EIS) measurement confirmed the excellent OER performance of the Ni(Fe)MOF/mKB14 composite. For practical applications, the Ni(Fe)MOF/mKB14 electrocatalyst was impregnated into commercial nickel foam (NF), where overpotentials of 247 and 291 mV at current densities of 10 and 50 mA cm-2, respectively, were realized. The activity was maintained for 30 h at the applied current density of 50 mA cm-2. More importantly, this work adds to the fundamental understanding of the in situ transformation of Ni(Fe)DMOF into OER-active α/β-Ni(OH)2, β/γ-NiOOH, and FeOOH with residual porosity inherited from the MOF structure, as seen by powder X-ray diffractometry and N2 sorption analysis. Benefitting from the porosity structure of the MOF precursor, the nickel-iron catalysts outperformed the solely Ni-based catalysts due to their synergistic effects and exhibited superior catalytic activity and long-term stability in OER. In addition, by introducing mKB as a conductive carbon additive in the MOF structure, a homogeneous conductive network was constructed to improve the electronic conductivity of the MOF/mKB composites. The electrocatalytic system consisting of earth-abundant Ni and Fe metals only is attractive for the development of efficient, practical, and economical energy conversion materials for efficient OER activity.

Dataset Information

Nanocasting SiO₂ into metal-organic frameworks imparts dual protection to high-loading Fe single-atom electrocatalysts.

Publications

Nanocasting SiO<sub>2</sub> into metal-organic frameworks imparts dual protection to high-loading Fe single-atom electrocatalysts.

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