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. 2020 Jul 16;5(29):18391–18396. doi: 10.1021/acsomega.0c02182

S/N Co-Doped Hollow Carbon Particles for Oxygen Reduction Electrocatalysts Prepared by Spontaneous Polymerization at Oil–Water Interfaces

Hiroya Abe †,‡,*, Kohei Nozaki §, Shu Sokabe ∥, Akichika Kumatani ‡,§,⊥,#, Tomokazu Matsue §, Hiroshi Yabu ‡,*
PMCID: PMC7391958  PMID: 32743215

Abstract

graphic file with name ao0c02182_0007.jpg

We herein report that sulfur and nitrogen co-doped hollow spherical carbon particles can be applied to oxygen reduction reaction (ORR) electrocatalysts prepared by calcination of polydopamine (PDA) hollow particles. The hollow structure of PDA was formed by auto-oxidative interfacial polymerization of dopamine at the oil and water interface of emulsion microdroplets. The PDA was used as the nitrogen source as well as a platform for sulfur-doping. The obtained sulfur and nitrogen co-doped hollow particles showed a higher catalytic activity than that of nonsulfur-doped particles and nonhollow particles. The high ORR activity of the calcined S-doped PDA hollow particles could be attributed to the combination of nitrogen and sulfur active sites and the large surface areas owing to a hollow spherical structure.

Introduction

Fuel cells and metal–air batteries have received much attention as next-generation batteries because of their high energy density and less environmental impact in terms of small emission of greenhouse effect gases.1,2 Pt-loaded carbon (Pt/C) has been used as a cathode of these battery devices because of its high catalytic activity for the oxygen reduction reaction (ORR).3 However, because Pt-based catalysts are less abundant and of high cost, nonplatinum-based catalysts are in demand. As alternative materials for Pt-based catalysts, heteroatom-doped carbon materials, such as nitrogen4−6 sulfur,7,8 boron,7,9 iron,10−12 cobalt,13,14 and so on, have been investigated through various methods.

The polymeric materials15−17 and metal–organic frameworks18−20 have been employed as precursors of those heteroatom-doped carbons in terms of the carbon and doping heteroatom sources. Among various polymeric precursors, polydopamine (PDA), which is automatically polymerized from dopamine by atmospheric oxidation, is one of the most promising materials because thin films of PDA spontaneously formed at the solid–liquid,21−23 the oil–water, and the air–water interfaces.24−26 Moreover, PDA can be doped with heteroatoms by a metal chelate, the Michael addition reaction, and the Schiff-base reaction.27 By calcination of heteroatom-doped PDA, heteroatom-doped carbon materials can be obtained easily.28−30

Structural control of highly active carbon materials is also one of the most significant issues in this field. In particular, hollow particles can reduce diffusion lengths for mass, multiple interfaces, low density, abundant exposed active sites, and kinetically favorable open structure, which are highly desirable for accelerating oxygen reduction.31,32 Some studies have been reported about creation of carbon hollow spheres by calcination of organic polymeric precursors by templating solid nanoparticles, including silica nanoparticles. Yuan group has investigated the PDA hollow particles templated as SiO2 nanoparticles.33 However, several steps are required for the removal of solid templates, and hazardous chemicals such as hydrofluoric acid or condensed NaOH solution have been used to remove the silica template. Therefore, a simple and safe synthetic process for creating carbon hollow spheres has been longed for.

We herein report the synthesis of hollow carbon spherical particles consisting of PDA and sulfur dopants by templating liquid oil droplets dispersed in an aqueous media. The emulsion-templating method can easily remove the template by alcohol and needs no surfactant.24,34,35 Because a mass production of catalysts is important for overcoming energy problems, we employed the emulsion-templating method for electrocatalysts. The calcination of oil droplet-templated hollow PDA spherical capsules with sulfur-doping allows higher onset potential and higher half-wave potential than those of nonhollow particles and nondoped particles. These results indicate that both structural control and heteroatom doping of PDA offer a new and a simple way for creating highly active sulfur and nitrogen co-doped carbons for ORR electrocatalysts.

Results and Discussion

Figure 1 shows a schematic illustration of formation of hollow spherical carbon particles. First, the sulfur (S)-doped PDA hollow particles were obtained by auto-oxidative interfacial polymerization of dopamine at the oil and water interface of emulsion microdroplets.21,26 In this study, the tetradecane or hexadecane was used as the oil phase because the oil has high boiling temperature and can be easily removed by washing with ethanol. The solution color after polymerization turned from transparent to brown, which implied formation of PDA37 (see Supporting Information, S1). By adding S dopant to the reaction solution, PDA can be doped with S atoms by compositing sulfur-containing components via the Michael addition reaction21 and ion interaction.38 The heteroatom-doped carbon particles were obtained by the calcination of the obtained S-doped hollow particles. Herein, we prepare four samples (PDA, S-PDA, HPDA, and S-HPDA) for comparison. PDA and S-PDA have no hollow structures because these particles were prepared without oil-templating. HPDA and S-HPDA were prepared under the oil emulsion, and these particles have hollow structures. Sulfur-doped particles (S-PDA and S-HPDA) were prepared by adding sodium 4-amino-1,5-naphthalenedisulfonate (4ANDSNa) into the reaction solution without and with oil emulsion, respectively.

Figure 1.

Figure 1

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Schematic image of the catalyst synthesis. Yellow: oil, blue: dopamine, red: sulfur components, brown: composite of PDA and sulfur dopant, and black: pyrolyzed carbon.

Among many sulfur components, 4ANDSNa, disodium 1,5-naphthalenedisulfonate (1,5NDSNa), and bismuthiol and thiocyanuric acid were chosen because these chemicals could be dissolved in water but not in oil (Figure S2). In these sulfur molecules, 4ANDSNa, 1,5NDSNa, and bismuthiol formed polymer films around the oil phase, thus we evaluated ORR activity of their pyrolyzed particles without the emulsion templating. From the linear sweep voltammetry (LSV) curves of the obtained particles (Figure S3), all sulfur candidates enhanced the ORR activity from the pPDA. 4ANDSNa showed the highest ORR in other sulfur source candidates, therefore, we used 4ANDSNa for the sulfur-doping.

Small granular aggregations (about 100 nm) of PDA and S-PDA (about 330 nm) were observed in scanning transmission electron microscopy (STEM) images (Figure 2a,c). The size of granular aggregations was comparable with that of PDA particles reported in the literature.39 On the other hand, hollow structures were observed in HPDA and S-HPDA samples (Figure 2b,d), and the sizes of hollow particles were about 800 and 1000 nm, respectively. Dopamine can adsorb and polymerize not only on the solid surface but also on the air and liquid surfaces to stabilize those interfaces, thereby the PDA formed on the oil droplet in emulsion solution, and eventually, hollow particles were obtained. The thickness of the hollow particles (HPDA and S-HPDA) was 31.3 ± 0.3 and 43.5 ± 3.5 nm, respectively. The particle size of S-PDA and shell thickness in S-HPDA were larger than those of nonsulfur-doped samples, which might be caused by chemical bonding and an electrostatic interaction between PDA and 4ANDSNa having amine and sulfonic acid groups.33 After the heat treatment for our pyrolized samples (pPDA, pS-PDA, pHPDA, and pS-HPDA), the shape of the obtained particles was checked by scanning electron microscopy (SEM) imaging, and a large change in shape was not observed (Figure S4).

Figure 2.

Figure 2

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STEM images of (a) PDA, (b) HPDA, (c) S-PDA, and (d) S-HPDA before pyrolysis. The magnified STEM images of HPDA and S-HPDA with thickness indicators were inserted in (b,d).

The Raman spectra of pPDA, pS-PDA, pHPDA, and pS-HPDA are shown in Figure 3. These spectra have D- and G-bands attributed to the carbon network structures at 1350 and 1580 cm–1, respectively, which indicate that all pyrolyzed samples have graphitic structures. The R value, which was the relative intensity ratio (I1350/I1580) of D- and G-bands, indicates the relative content of the graphitic carbon network. Thus, the R value shows quality of formed carbon materials. The R value of pHPDA (0.92) was larger than that of pPDA (0.79). Similarly, the R value of the pS-HPDA (0.86) was larger than that of the pS-PDA (0.83). These results suggest that hollow carbon particles have higher content of the defect structure than solid spherical carbon particles. The graphitic degrees can be determined from a half-width (Δν cm–1) of the G-band.40 Short half-width is the carbon with a high graphitic degree. Δν of pPDA, pS-PDA, pHPDA, and pS-HPDA were 46, 44, 40, and 46 cm–1, respectively, which indicates that the S doping did not have an effect on the graphitic degrees.

Figure 3.

Figure 3

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Raman spectrum of pyrolyzed particles; pPDA (gray line), pHPDA (black line), pS-PDA (orange line), and pS-HPDA (red line).

A specific surface area of these catalysts was evaluated by the nitrogen (N2) adsorption experiment. The adsorption–desorption isotherms and pore size distribution are shown in Figure 4a,b. The adsorption curve of our catalysts showed a type IV curve, indicating the existence of mesopores.41 Our catalysts distributed to the micropores (<2 nm) and mesopores with sizes ranging from 2 to 50 nm (Figure 4b), and hollow particles enhanced these pore volumes. The specific surface area of the pHPDA was 70.299 m2/g, which was larger than that of the pPDA (39.682 m2/g). The specific surface area of the pS-HPDA was 75.473 m2/g, which was larger than that of the pS-PDA (18.179 m2/g) and the other obtained catalysts. These results indicate that the hollow structure enlarges the specific surface area.

Figure 4.

Figure 4

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(a) Adsorption–desorption isotherms and (b) pore size distribution of pPDA (black dot), pHPDA (black solid), pS-PDA (red dot), and pS-HPDA (red solid).

X-ray photoelectron spectroscopy (XPS) spectra of pPDA, pHPDA, pS-PDA, and pS-HPDA are shown in Figures 5 and S5. Peaks attributed to O 1s, N 1s, C 1s, and S 2p were obtained from the pS-PDA and the pS-HPDA. Both in pPDA and in pHPDA, peaks attributed to the O 1s, N 1s, and C 1s orbitals were also observed, but peak attributed to the S 2p orbitals around 165 eV was not observed. The doping ratio of N and S in the pS-HPDA was 3.1 and 0.4 at. %, respectively, which were higher values than that of N (2.5 at. %) and S (0 at. %) in the pHPDA. From these results, sulfur atoms originated from 4ANDSNa was successfully doped into PDA even though after calcination.

Figure 5.

Figure 5

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XPS S 2p spectra of pyrolyzed particles: (a) pPDA and pS-PDA and (b) pHPDA and pS-HPDA.

LSV curves of the obtained samples measured in O2-saturated 0.1 M KOH are shown in Figure 6a, and ORR activities of the prepared samples are summarized in Table 1. The maximum current density of pHPDA (5.95 mA/cm2) was higher than that of pPDA (5.10 mA/cm2). The Eonset potential of both samples was 0.863 V versus reversible hydrogen electrode (RHE). The maximum current density of pS-HPDA (6.11 mA/cm2) was higher than that of pS-PDA (5.55 mA/cm2). Furthermore, pS-HPDA showed highest Eonset (0.903 V vs RHE) compared to other catalyst electrodes, which were closest to that of Pt/C (1.013 V vs RHE). The number of reaction electrons of pS-HPDA (3.6 at 0.6 V) was largest comparing other pyrolyzed catalysts, which was close to four electron number reaction (Figure 6b). Although our catalyst had a low sulfur content (0.4 at. %), the ORR activity enhanced sufficiently. Similarly, in a previous study,42 a pristine carbon black containing very low sulfur atoms (0.08 at. %) showed lower activity (Eonset = 0.804 V) than our catalysts (Eonset = 0.903 V). From this comparison, the sulfur content of Ketjenblack is not sufficient for inducing the high ORR activity. Therefore, our sulfur-doping approach is efficient for the enhancement of the ORR activity.

Figure 6.

Figure 6

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(a) LSV of pyrolyzed particles at 1600 rpm in O2-saturated 0.1 M KOH. (b) Reaction electron number of the obtained samples. (c) LSV curves of pPDA (solid line) and pHPDA (broken line) at 0 rpm in O2-saturated 0.1 M KOH. (d) LSV curves of pS-PDA (solid line) and pS-HPDA (broken line) at 0 rpm in O2-saturated 0.1 M KOH. (e) Durability test of Pt/C and pS-HPDA.

Table 1. Summary of Onset Potential, Half-Wave Potential, Current Density, and Peak Area of Obtained Catalysts.

  Eonset (V vs RHE) current density (mA/cm2) reaction amount (mC)
pPDA 0.863 –5.10 7.45
pHPDA 0.863 –5.95 13.9
pS-PDA 0.863 –5.55 25.1
pS-HPDA 0.903 –6.11 35.8
Pt/C 1.013 –6.69  
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The LSV curves of the obtained catalysts at 0 rpm are shown in Figure 6c,d to evaluate electrochemical active area of catalysts. The reduction peaks of all obtained samples were observed at around 0.75 V and that of pS-HPDA shifted to the most positive (0.80 V). Moreover, the current amount of pS-HPDA (35.8 mC) was largest than other catalysts. These trends are similar to specific area from Brunauer–Emmett–Teller (BET) analysis and the amount of S atoms in the catalyst from XPS analysis, thus the catalysts were successfully improved by changing the catalyst structure and S-doping.

The H2O2 production of our catalysts is shown in Figure S6. The pS-HPDA showed the lowest production of H2O2 among the prepared samples and the previous literature about sulfur-doped hollow PDA particles created by the silica particle-templating.33 Because the production of H2O2 for our catalysts is still higher than Pt/C (under 10%), we are trying to reduce the production of H2O2 by adding metal ions, which will be published in the next article. This result indicates that oil-templating and S-doping are an efficient method for reducing the H2O2 production.

Finally, the chronoamperogram of the pS-HPDA and Pt/C for 50,000 s is shown in Figure 6e to evaluate their durability. After 50,000 s, the current density of pS-HPDA was maintained at 83% from the initial current density although that of Pt/C decreased to 63%. These results indicate that S-doped PDA-calcined hollow particles have a much higher catalyst stability than Pt/C. Pt/C shows the desorption and aggregation of Pt due to the application of a long-term voltage,43 whereas, in our catalysts, sulfur and nitrogen atoms were embedded into the carbon, which may lead the high stability.

Conclusions

For development of ORR with the nonmetal carbon catalyst, it is important to maintain the catalyst structure and heteroatom-doping. In this study, we synthesized one-pot hollow PDA particles doped with sulfur atoms by using oil–water interfacial polymerization. The hollow particles were prepared from the oil-templated PDA from which oil droplets were easily removed by using low-class alcohol. The hollow-structured and sulfur-doped catalysts showed higher catalytic ORR activity than nonhollow-structured and nonsulfur-doped catalysts. This improvement is caused by efficiently doping active site sulfur atoms and hollow structures.

Experimental Methods

Chemicals

Dopamine hydrochloride and tris(hydroxymethyl) aminomethane (Tris–HCl) were purchased from Sigma-Aldrich, St. Louis. Hexane and dichloromethane were purchased from Wako Pure Chemical Industries, Ltd., Tokyo. 4ANDSNa was purchased from Tokyo Chemical Industry, Ltd. All chemicals were used as received.

Catalyst Preparation

A sulfur-doped carbon was prepared by following procedures. 4ANDSNa was used as a sulfur dopant. 4ANDSNa (50 mg) was dissolved in 58.8 mL of 0.02 M sodium hydroxide, and 1.2 mL tetradecane or hexadecane was added into the aqueous solution and homogenized it for 10 min to form an emulsion by using an ultrasonic homogenizer. After the solution turned from transparent to opaque, 240 mg of dopamine hydrochloride was injected into the solution with maintaining the pH value of the solution at 10 by adding 1 M sodium hydroxide solution. The reaction was allowed for 3 h with stirring at room temperature. To obtain sulfur-doped hollow PDA particles (S-PDA), the precipitates were collected by centrifugation, and then, the collected specimen was washed with ethanol and deionized water for three times and dried at 80 °C overnight in an oven. Finally, pyrolized sulfur and nitrogen co-doped hollow PDA particles (pS-HPDA) were obtained by the calcination of 4ANDSNa-doped hollow carbon at 800 °C for 2 h under a nitrogen atmosphere in a vacuum furnace (FT-1200R-100SP, FULL-TECH FURNACE Co., Ltd., Japan).

For comparison with pS-HPDA, hollow PDA carbon particles (pHPDA) and nonhollow carbon particles of sulfur-doping (pS-PDA) and nonsulfur-doping (pPDA) were evaluated.

Characterizations

The structures of the obtained particles were observed by using SEM (S-5200, Hitachi). The shell thickness was calculated from STEM images by using ImageJ software. Raman spectroscopy (LabRAM HR-800, Horiba, Japan) with 532 nm laser excitation was used in order to determine the quality of carbon networks in the calcined samples. An XPS (KRATOS AXIS-Ultra DLD, Shimazu, Japan) was performed for determining an elemental ratio of each atom and electronic states of the elements of the obtained samples.

The BET surface areas of the obtained particles were measured by using a surface area analyzer (QUADRASORB evo, Quantachrome Instruments, Japan).

Electrochemical Measurement

The ORR performance was evaluated by LSV and cyclic voltammetry measurements using a potentiostat (2325, BAS Co., Ltd., Japan). Catalyst ink for each sample was prepared by dispersing 0.84 mg of the catalyst particles in a mixture consisting of 6 μL Nafion (527084, Sigma-Aldrich, USA), 334 μL isopropyl alcohol, and 60 μL water with sonication for 5 min. Then, 20 μL of the ink was cast onto a glassy carbon (BAS Co., Ltd., Japan) for a rotating ring-disk electrode (RRDE) (4 mm diameter, BAS Co., Ltd., Japan) and dried. The weight of the catalyst on the electrode was 307 μg/cm2. A Pt wire and an Ag/AgCl electrode were inserted into the electrolyte as reference and counter electrodes, respectively.

The potential against the Ag/AgCl reference electrode was converted to the RHE scale using the following equation

graphic file with name ao0c02182_m001.jpg 1

The number of electrons (n) involved in the ORR was calculated, according to the K–L equation

graphic file with name ao0c02182_m002.jpg 2

where J, Jk, and Jd are the measured, kinetic, and diffusion-limiting current, respectively; F is the Faraday constant (96,485 C/mol); A is the electrode area (0.1256 cm2); k is the rate constant for oxygen reduction (m/s); DO2 is the diffusion coefficient of O2 in the electrolyte (1.93 × 10–5 cm2/s); ν is the viscosity of the electrolyte solution (1.009 × 10–5 cm2/s); CO2 is the saturated concentration of O2 in the electrolyte (1.26 × 10–6 mol/cm3); and ω is the angular rotation rate. n was also calculated using the RRDE results and the following equation

graphic file with name ao0c02182_m003.jpg 3

where JD and JR are the current densities of disk and ring electrodes, respectively, and N is the capture efficiency (0.42).

The H2O2 yield can be determined by the following equation

graphic file with name ao0c02182_m004.jpg 4

The durability of catalysts was evaluated from the i–t chronoamperometric responses of the prepared carbon catalyst and Pt/C catalyst in O2-saturated 0.1 M KOH at 0.6 V (vs RHE) for 50,000 s with a rotation speed of 1600 rpm.

Acknowledgments

H.A. thanks KAKENHI, JSPS (no. 19K15598), Research Institutes Ensemble Grant for young researchers and FRIS Creative Interdisciplinary Collaboration Program from Tohoku University for financial support. H.Y. thanks KAKENHI, JSPS (nos. 18H05482, 18H05322, 19KK0357, and 20H04625) for financial support. H.A., A.K., and H.Y. thank to AIMR Fusion research from Tohoku University for financial support.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.0c02182.

  • Photograph of prepared solution, chemical structures, LSV curves, SEM images, XPS spectra for N 1s, and H2O2 production of calcined samples (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao0c02182_si_001.pdf (358.2KB, pdf)

References

  1. Debe M. K. Electrocatalyst Approaches and Challenges for Automotive Fuel Cells. Nature 2012, 486, 43–51. 10.1038/nature11115. [DOI] [PubMed] [Google Scholar]
  2. Pei P.; Wang K.; Ma Z. Technologies for Extending Zinc-Air Battery’s Cyclelife: A Review. Appl. Energy 2014, 128, 315–324. 10.1016/j.apenergy.2014.04.095. [DOI] [Google Scholar]
  3. Katsounaros I.; Cherevko S.; Zeradjanin A. R.; Mayrhofer K. J. J. Oxygen Electrochemistry as a Cornerstone for Sustainable Energy Conversion. Angew. Chem., Int. Ed. 2014, 53, 102–121. 10.1002/anie.201306588. [DOI] [PubMed] [Google Scholar]
  4. Gong K.; Du F.; Xia Z.; Durstock M.; Dai L. Nitrogen-Doped Carbon Nanotube Arrays with High Electrocatalytic Activity for Oxygen Reduction. Science 2009, 323, 760–764. 10.1126/science.1168049. [DOI] [PubMed] [Google Scholar]
  5. Yu Y. M.; Zhang J. H.; Xiao C. H.; Zhong J. D.; Zhang X. H.; Chen J. H. High Active Hollow Nitrogen-Doped Carbon Microspheres for Oxygen Reduction in Alkaline Media. Fuel Cells 2012, 12, 506–510. 10.1002/fuce.201100111. [DOI] [Google Scholar]
  6. Guo D.; Shibuya R.; Akiba C.; Saji S.; Kondo T.; Nakamura J. Active Sites of Nitrogen-Doped Carbon Materials for Oxygen Reduction Reaction Clarified Using Model Catalysts. Science 2016, 351, 361–365. 10.1126/science.aad0832. [DOI] [PubMed] [Google Scholar]
  7. Li W.; Yang D.; Chen H.; Gao Y.; Li H. Sulfur-Doped Carbon Nanotubes as Catalysts for the Oxygen Reduction Reaction in Alkaline Medium. Electrochim. Acta 2015, 165, 191–197. 10.1016/j.electacta.2015.03.022. [DOI] [Google Scholar]
  8. Yang Z.; Yao Z.; Li G.; Fang G.; Nie H.; Liu Z.; Zhou X.; Chen X. a.; Huang S. Sulfur-Doped Graphene as an Efficient Metal-Free Cathode Catalyst for Oxygen Reduction. ACS Nano 2012, 6, 205–211. 10.1021/nn203393d. [DOI] [PubMed] [Google Scholar]
  9. Zhao Z.; Li M.; Zhang L.; Dai L.; Xia Z. Design Principles for Heteroatom-Doped Carbon Nanomaterials as Highly Efficient Catalysts for Fuel Cells and Metal-Air Batteries. Adv. Mater. 2015, 27, 6834–6840. 10.1002/adma.201503211. [DOI] [PubMed] [Google Scholar]
  10. Abe H.; Hirai Y.; Ikeda S.; Matsuo Y.; Matsuyama H.; Nakamura J.; Matsue T.; Yabu H. Fe Azaphthalocyanine Unimolecular Layers (Fe AzULs) on Carbon Nanotubes for Realizing Highly Active Oxygen Reduction Reaction (ORR) Catalytic Electrodes. NPG Asia Mater 2019, 11, 57. 10.1038/s41427-019-0154-6. [DOI] [Google Scholar]
  11. Zitolo A.; Goellner V.; Armel V.; Sougrati M.-T.; Mineva T.; Stievano L.; Fonda E.; Jaouen F. Identification of Catalytic Sites for Oxygen Reduction in Iron- and Nitrogen-Doped Graphene Materials. Nat. Mater. 2015, 14, 937–942. 10.1038/nmat4367. [DOI] [PubMed] [Google Scholar]
  12. Lee J.-S. M.; Sarawutanukul S.; Sawangphruk M.; Horike S. Porous Fe-N-C Catalysts for Rechargeable Zinc-Air Batteries from an Iron-Imidazolate Coordination Polymer. ACS Sustain. Chem. Eng. 2019, 7, 4030–4036. 10.1021/acssuschemeng.8b05403. [DOI] [Google Scholar]
  13. Yu M.; Wang Z.; Hou C.; Wang Z.; Liang C.; Zhao C.; Tong Y.; Lu X.; Yang S. Nitrogen-Doped Co3O4Mesoporous Nanowire Arrays as an Additive-Free Air-Cathode for Flexible Solid-State Zinc–Air Batteries. Adv. Mater. 2017, 29, 1602868. 10.1002/adma.201602868. [DOI] [PubMed] [Google Scholar]
  14. Liang Y.; Li Y.; Wang H.; Zhou J.; Wang J.; Regier T.; Dai H. Co3O4 Nanocrystals on Graphene as a Synergistic Catalyst for Oxygen Reduction Reaction. Nat. Mater. 2011, 10, 780–786. 10.1038/nmat3087. [DOI] [PubMed] [Google Scholar]
  15. Nabae Y.; Kuang Y.; Chokai M.; Ichihara T.; Isoda A.; Hayakawa T.; Aoki T. High Performance Pt-Free Cathode Catalysts for Polymer Electrolyte Membrane Fuel Cells Prepared from Widely Available Chemicals. J. Mater. Chem. A 2014, 2, 11561–11564. 10.1039/c4ta01828a. [DOI] [Google Scholar]
  16. Subramanian N. P.; Li X.; Nallathambi V.; Kumaraguru S. P.; Colon-Mercado H.; Wu G.; Lee J.-W.; Popov B. N. Nitrogen-Modified Carbon-Based Catalysts for Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells. J. Power Sources 2009, 188, 38–44. 10.1016/j.jpowsour.2008.11.087. [DOI] [Google Scholar]
  17. Shao M.; Chang Q.; Dodelet J.-P.; Chenitz R. Recent Advances in Electrocatalysts for Oxygen Reduction Reaction. Chem. Rev. 2016, 116, 3594–3657. 10.1021/acs.chemrev.5b00462. [DOI] [PubMed] [Google Scholar]
  18. Li L.; He J.; Wang Y.; Lv X.; Gu X.; Dai P.; Liu D.; Zhao X. Metal-Organic Frameworks: A Promising Platform for Constructing Non-Noble Electrocatalysts for the Oxygen-Reduction Reaction. J. Mater. Chem. A 2019, 7, 1964–1988. 10.1039/c8ta11704g. [DOI] [Google Scholar]
  19. Kaneti Y. V.; Zhang J.; He Y.-B.; Wang Z.; Tanaka S.; Hossain M. S. A.; Pan Z.-Z.; Xiang B.; Yang Q.-H.; Yamauchi Y. Fabrication of an MOF-Derived Heteroatom-Doped Co/CoO/Carbon Hybrid with Superior Sodium Storage Performance for Sodium-Ion Batteries. J. Mater. Chem. A 2017, 5, 15356–15366. 10.1039/c7ta03939e. [DOI] [Google Scholar]
  20. Wang C.; Kim J.; Tang J.; Na J.; Kang Y. M.; Kim M.; Lim H.; Bando Y.; Li J.; Yamauchi Y. Large-Scale Synthesis of MOF-Derived Superporous Carbon Aerogels with Extraordinary Adsorption Capacity for Organic Solvents. Angew. Chem., Int. Ed. 2020, 59, 2066–2070. 10.1002/anie.201913719. [DOI] [PubMed] [Google Scholar]
  21. Lee H.; Dellatore S. M.; Miller W. M.; Messersmith P. B. Mussel-Inspired Surface Chemistry for Multifunctional Coatings. Science 2007, 318, 426–430. 10.1126/science.1147241. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Li Z.; Zhang X.; Wang S.; Yang Y.; Qin B.; Wang K.; Xie T.; Wei Y.; Ji Y. Polydopamine Coated Shape Memory Polymer: Enabling Light Triggered Shape Recovery, Light Controlled Shape Reprogramming and Surface Functionalization. Chem. Sci. 2016, 7, 4741–4747. 10.1039/c6sc00584e. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Kohri M.; Kohma H.; Shinoda Y.; Yamauchi M.; Yagai S.; Kojima T.; Taniguchi T.; Kishikawa K. A Colorless Functional Polydopamine Thin Layer as a Basis for Polymer Capsules. Polym. Chem. 2013, 4, 2696. 10.1039/c3py00181d. [DOI] [PubMed] [Google Scholar]
  24. Cui J.; Wang Y.; Postma A.; Hao J.; Hosta-Rigau L.; Caruso F. Monodisperse Polymer Capsules: Tailoring Size, Shell Thickness, and Hydrophobic Cargo Loading via Emulsion Templating. Adv. Funct. Mater. 2010, 20, 1625–1631. 10.1002/adfm.201000209. [DOI] [Google Scholar]
  25. Ni Y.-Z.; Jiang W.-F.; Tong G.-S.; Chen J.-X.; Wang J.; Li H.-M.; Yu C.-Y.; Huang X.-h.; Zhou Y.-F. Preparation of Polydopamine Nanocapsules in a Miscible Tetrahydrofuran-Buffer Mixture. Org. Biomol. Chem. 2015, 13, 686–690. 10.1039/c4ob02080d. [DOI] [PubMed] [Google Scholar]
  26. Abe H.; Matsue T.; Yabu H. Reversible Shape Transformation of Ultrathin Polydopamine-Stabilized Droplet. Langmuir 2017, 33, 6404–6409. 10.1021/acs.langmuir.7b01355. [DOI] [PubMed] [Google Scholar]
  27. Liu Y.; Ai K.; Lu L. Polydopamine and Its Derivative Materials: Synthesis and Promising Applications in Energy, Environmental, and Biomedical Fields. Chem. Rev. 2014, 114, 5057–5115. 10.1021/cr400407a. [DOI] [PubMed] [Google Scholar]
  28. Abe H.; Nozaki K.; Kumatani A.; Matsue T.; Yabu H. N- and Fe-Containing Carbon Films Prepared by Calcination of Polydopamine Composites Self-Assembled at Air/Water Interface for Oxygen Reduction Reaction. Chem. Lett. 2018, 48, 102. 10.1246/cl.180872. [DOI] [Google Scholar]
  29. Wu X.; Niu Y.; Feng B.; Yu Y.; Huang X.; Zhong C.; Hu W.; Li C. M. Mesoporous Hollow Nitrogen-Doped Carbon Nanospheres with Embedded MnFe2O4/Fe Hybrid Nanoparticles as Efficient Bifunctional Oxygen Electrocatalysts in Alkaline Media. ACS Appl. Mater. Interfaces 2018, 10, 20440–20447. 10.1021/acsami.8b04012. [DOI] [PubMed] [Google Scholar]
  30. Qu K.; Wang Y.; Zhang X.; Chen H.; Li H.; Chen B.; Zhou H.; Li D.; Zheng Y.; Dai S. Polydopamine-Derived, In Situ N-Doped 3D Mesoporous Carbons for Highly Efficient Oxygen Reduction. ChemNanoMat 2018, 4, 417–422. 10.1002/cnma.201800032. [DOI] [Google Scholar]
  31. Ding D.; Shen K.; Chen X.; Chen H.; Chen J.; Fan T.; Wu R.; Li Y. Multi-Level Architecture Optimization of MOF-Templated Co-Based Nanoparticles Embedded in Hollow N-Doped Carbon Polyhedra for Efficient OER and ORR. ACS Catal. 2018, 8, 7879–7888. 10.1021/acscatal.8b02504. [DOI] [Google Scholar]
  32. Wang X.; Feng J.; Bai Y.; Zhang Q.; Yin Y. Synthesis, Properties, and Applications of Hollow Micro-/Nanostructures. Chem. Rev. 2016, 116, 10983–11060. 10.1021/acs.chemrev.5b00731. [DOI] [PubMed] [Google Scholar]
  33. Zhao H.; Zhu Y.-P.; Ge L.; Yuan Z.-Y. Nitrogen and Sulfur Co-Doped Mesoporous Hollow Carbon Microspheres for Highly Efficient Oxygen Reduction Electrocatalysts. Int. J. Hydrogen Energy 2017, 42, 19010–19018. 10.1016/j.ijhydene.2017.06.172. [DOI] [Google Scholar]
  34. Lei C.; Li Q.; Yang L.; Deng F.; Li J.; Ye Z.; Wang Y.; Zhang Z. Controlled Reversible Buckling of Polydopamine Spherical Microcapsules: Revealing the Hidden Rich Phenomena of Post-Buckling of Spherical Polymeric Shells. Soft Matter 2019, 15, 6504–6517. 10.1039/c9sm00705a. [DOI] [PubMed] [Google Scholar]
  35. Zhai Y.; Whitten J. J.; Zetterlund P. B.; Granville A. M. Synthesis of Hollow Polydopamine Nanoparticles Using Miniemulsion Templating. Polymer 2016, 105, 276–283. 10.1016/j.polymer.2016.10.038. [DOI] [Google Scholar]
  36. Guan B. Y.; Yu L.; Lou X. W. Formation of Asymmetric Bowl-Like Mesoporous Particles via Emulsion-Induced Interface Anisotropic Assembly. J. Am. Chem. Soc. 2016, 138, 11306–11311. 10.1021/jacs.6b06558. [DOI] [PubMed] [Google Scholar]
  37. Xu Z. Mechanics of Metal-Catecholate Complexes: The Roles of Coordination State and Metal Types. Sci. Rep. 2013, 3, 2914. 10.1038/srep02914. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Ang J. M.; Du Y.; Tay B. Y.; Zhao C.; Kong J.; Stubbs L. P.; Lu X. One-Pot Synthesis of Fe(III)-Polydopamine Complex Nanospheres: Morphological Evolution, Mechanism, and Application of the Carbonized Hybrid Nanospheres in Catalysis and Zn-Air Battery. Langmuir 2016, 32, 9265–9275. 10.1021/acs.langmuir.6b02331. [DOI] [PubMed] [Google Scholar]
  39. Knight D. S.; White W. B. Characterization of Diamond Films by Raman Spectroscopy. J. Mater. Res. 1989, 4, 385–393. 10.1557/jmr.1989.0385. [DOI] [Google Scholar]
  40. Fatima S.; Ali S. I.; Iqbal M. Z.; Rizwan S. The High Photocatalytic Activity and Reduced Band Gap Energy of La and Mn Co-Doped BiFeO3/Graphene Nanoplatelet (GNP) Nanohybrids. RSC Adv. 2017, 7, 35928–35937. 10.1039/c7ra04281g. [DOI] [Google Scholar]
  41. Cheng G.-C.; Li G.-L.; Liu C.-D.; Yuan L.-F.; Chen W.-W.; Hao C. Efficient Synthesis of Nitrogen- and Sulfur-Co-Doped Ketjenblack with a Single-Source Precursor for Enhancing Oxygen Reduction Reaction Activity. Chem.—Eur. J. 2017, 23, 3674–3682. 10.1002/chem.201604930. [DOI] [PubMed] [Google Scholar]
  42. Li Y.; Li Y.; Zhu E.; McLouth T.; Chiu C.-Y.; Huang X.; Huang Y. Stabilization of High-Performance Oxygen Reduction Reaction Pt Electrocatalyst Supported on Reduced Graphene Oxide/Carbon Black Composite. J. Am. Chem. Soc. 2012, 134, 12326–12329. 10.1021/ja3031449. [DOI] [PubMed] [Google Scholar]

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