Metal single-atom catalysts (M-SACs) have emerged as an attractive concept for promoting heterogeneous reactions, but the synthesis of high-loading M-SACs remains a challenge. Here, we report a multilayer stabilization strategy for constructing M-SACs in nitrogen-, sulfur- and fluorine-co-doped graphitized carbons (M = Fe, Co, Ru, Ir and Pt). Metal precursors are embedded into perfluorotetradecanoic acid multilayers and are further coated with polypyrrole prior to pyrolysis. Aggregation of the metals is thus efficiently inhibited to achieve M-SACs with a high metal loading (~16 wt%). Fe-SAC serves as an efficient oxygen reduction catalyst with half-wave potentials of 0.91 and 0.82 V (versus reversible hydrogen electrode) in alkaline and acid solutions, respectively. Moreover, as an air electrode in zinc–air batteries, Fe-SAC demonstrates a large peak power density of 247.7 mW cm−2 and superior long-term stability. Our versatile method paves an effective way to develop high-loading M-SACs for various applications.
Nitrogen-doped graphitic carbon materials hosting single-atom
iron
(Fe–N–C) are major non-precious metal catalysts for
the oxygen reduction reaction (ORR). The nitrogen-coordinated Fe sites
are described as the first coordination sphere. As opposed to the
good performance in ORR, that in the oxygen evolution reaction (OER)
is extremely poor due to the sluggish O–O coupling process,
thus hampering the practical applications of rechargeable zinc (Zn)–air
batteries. Herein, we succeed in boosting the OER activity of Fe–N–C
by additionally incorporating phosphorus atoms into the second coordination
sphere, here denoted as P/Fe–N–C. The resulting material
exhibits excellent OER activity in 0.1 M KOH with an overpotential
as low as 304 mV at a current density of 10 mA cm–2. Even more importantly, they exhibit a remarkably small ORR/OER
potential gap of 0.63 V. Theoretical calculations using first-principles
density functional theory suggest that the phosphorus enhances the
electrocatalytic activity by balancing the *OOH/*O adsorption at the
FeN4 sites. When used as an air cathode in a rechargeable
Zn–air battery, P/Fe–N–C delivers a charge–discharge
performance with a high peak power density of 269 mW cm–2, highlighting its role as the state-of-the-art bifunctional oxygen
electrocatalyst.
The development of iron and nitrogen co‐doped carbon (FeNC) electrocatalysts for the oxygen reduction reaction (ORR) in proton‐exchange membrane fuel cells (PEMFCs) is a grand challenge due to the low density of accessible FeN4 sites. Here, an in situ trapping strategy using nitrogen‐rich molecules (e.g., melamine, MA) is demonstrated to enhance the amount of accessible FeN4 sites in FeNC electrocatalysts. The melamine molecules can participate in the coordination of Fe ions in zeolitic imidazolate frameworks to form FeN6 sites within precursors. These FeN6 sites are then converted into atomically dispersed FeN4 sites during a pyrolytic process. Remarkably, the FeNC/MA exhibits a high single‐atom Fe content (3.5 wt.%), a large surface area (1160 m2 g−1), and a high density of accessible FeN4 sites (45.7 × 1019 sites g−1). As a result, FeNC/MA shows a much enhanced ORR activity with a half‐wave potential of 0.83 V (vs the reversible hydrogen electrode) in a 0.5 m H2SO4 electrolyte solution and a good performance in a PEMFC system with an activity of 80 mA cm−2 at 0.8 V under 1.0 bar H2/air. This work offers a promising approach toward high‐performance carbon‐based ORR electrocatalysts.
We report a F-doped FeNC catalyst with improved ORR performance. The enhanced performance is associated with the large BET surface area, abundant single Fe atoms, and strong electron-withdrawing F-doping.
The graphene aerogels supporting Ag and CeO 2 nanoparticles (NPs) (Ag/CeO 2 /GA) with bifunctional performances have been fabricated by a modified gelatinization reaction method. Through the control of GO concentration and ultrasonic-assisted prereduction process, the small NPs can be dispersed highly into the porous structure of GA. The integration of a hierarchical porous structure and a synergistic effect between CeO 2 and Ag NPs grant them bifunctional properties of organic pollutant removing (100% of methylene blue and 81.8% of bisphenol A were degraded within 12 min and 4 h, respectively), and antimicrobial activity against Escherichia coli (MIC 100%Ag = 7.5 ppm; MBC 100%Ag = 11.3 ppm). The possible mechanism is the improved photocatalytic performance of CeO 2 /GA by a unique surface plasmonic effect of Ag NPs due to increasing light absorption and photoconductivity for photoexcited holes and electrons. Therefore, the holes and radicals (especially •OH) can be produced continuously and efficiently from Ag/ CeO 2 /GA, which can remove organic pollution from water efficiently, while protecting the water from bacterial pollution. Moreover, a good recycling stability and biocompatibility suggest that such bifunctional material has a great promise in water purification applications.
Basic helix-loop-helix (bHLH) proteins are highly conserved DNA-binding transcription factors of a large superfamily. Animal bHLH proteins play important regulatory roles in various developmental processes such as neurogenesis, myogenesis, heart development, and hematopoiesis. The jewel wasp (Nasonia vitripennis) is a good model organism of hymenoptera insects for studies of developmental and evolutionary genetics. In this study, we identified 48 bHLH genes in the genome of N. vitripennis. According to phylogenetic analysis, based on N. vitripennis bHLH (NvbHLH) motif sequences and structural domain distribution in their full-length protein sequences, the identified NvbHLH genes were classified into 36 bHLH families with 19, 12, 9, 1, 6, and 1 member(s) in groups A, B, C, D, E, and F, respectively. Our classification to the identified NvbHLH family members confirms GenBank annotations for 21 of the 48 NvbHLH proteins and provides useful information for further characterization and annotation of the remaining 27 NvbHLH proteins. Compared to other insect species, N. vitripennis has the lowest number of bHLH family members. No NvbHLH members have been found in the families Net, MyoRa, and PTFa, while all other insect species have at least one member in each of the families. These data constitute a solid basis for further investigations into the functions of bHLH proteins in developmental regulation of N. vitripennis.
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