Supplementary Information

Fe3O4 Nanoparticles Encapsulated in Single-Atom Fe-N-C

towards Efficient Oxygen Reduction Reaction: Effect of the

Micro and Macro Pores

Shuqi Hu,a Wenpeng Ni,a Daihui Yang,a Chao Ma,a Jiaheng Zhang,b Junfei Duan,c

Yang Gao*a and Shiguo Zhang*a

a College of Materials Science and Engineering, Hunan province key laboratory for

advanced carbon materials and applied technology, Hunan University, Changsha,

410082, P. R. China.

b School of Materials Science and Engineering, Harbin Institute of Technology

Shenzhen, 518055, P. R. China

c School of Materials Science and Engineering, Changsha University of Science and

Technology, Changsha, 410004, P. R. China.

*Corresponding authors. E-mail: ygao@hnu.edu.cn; zhangsg@hnu.edu.cn.

Figure S1. (a) TEM image of the surface of a selected nanoparticle in Fe3O4@FeNC.

(b) TEM image of Fe3O4@FeNC with the meso-pores highlighted.

Figure S2. EDX analysis of in Figure 2f. Characteristic peaks for C, N, O and Fe are

marked. The signal of Zn located at ~8.6 keV was not detected.

Figure S3. (a) Overall XPS spectra of overall survey spectra of the Fe3O4@FeNC,

Macro- FeNC and Micro-FeNC. (b) High resolution spectrum for Fe 2p peak of

Fe3O4@FeNC.

Table S1. Atomic ratios of C, N and O in the as-prepared samples.

Sample C atom N atom O atom N/C ratio

Fe3O4@FeNC 96.71% 1.28% 2.01% 0.013

Macro-FeNC 95.92% 1.35% 2.73% 0.014

Micro-FeNC 95.63% 1.07% 3.30% 0.011

Figure S4. (a) High-resolution C 1s spectra with deconvolutions of Fe3O4@FeNC,

Macro-FeNC and Micro-FeNC. (b) The corresponding atomic ratios of different C

species.

Figure S5. Electrochemical measurements of the as-prepared catalysts in alkaline

solution: (a) CV curves of Fe3O4@FeNC in N2 or O2-saturated alkaline solution with

the scan rate of 50 mV s-1. (b) LSV curves of Fe3O4@FeNC at different rotation

speeds. (c) The corresponding Koutecky-Levich plot of b. (d) RRDE measurement of

the as-prepared catalysts.

Figure S6. Electrochemical measurements of the as-prepared catalysts in acid

solution: (a) LSV curves in O2-saturated acid solution. (b) Corresponding half-wave

potentials and limiting current densities. (c) Tafel plot. (d) The H2O2 yields and

electron transfer numbers obtained from RRDE measurements. Same color scheme is

used for figure a, c and d.

Figure S7. Electrochemical measurements of the as-prepared catalysts in acid

solution: (a) CV curves of Fe3O4@FeNC in N2 or O2-saturated acid solution with the

scan rate of 50 mV s-1. (b) LSV curves of Fe3O4@FeNC at different rotation speeds.

(c) The corresponding Koutecky-Levich plot of b. (d) RRDE measurement of the as-

prepared catalysts.

Figure S8. CV curves of the as-prepared catalysts at different scan rates in N2-

saturated alkaline solution.

Figure S9. Current densities as a function of the scan rate based on the CV curves in

Figure S8.

Figure S10. (a) LSV curves of Fe3O4@FeNC before and after the addition of 10 mM

KSCN in 0.1 M HClO4. (b) LSV curves of KSCN poisoned Fe3O4@FeNC in 0.1 M

KOH.

Figure S11. Slab models for O2 adsorption on the surface of (a) individual Fe-N4-C

active site and (b) Fe-N4-C supported by Fe3O4. (c, d) The corresponding top views.

Table S2. ORR activity of recently reported catalysts in 0.1 M KOH aqueous solution.

Catalysts Mass loading

(mg cm-2)

Onset potential

(V vs. RHE)

Half-wave potential

(V vs. RHE)

Tafel slope(mV dec-1 )

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