Supporting information
A facile strategy to fabricate nitrogen-doped graphene aerogel supported Fe3N nanoparticles as efficient electrocatalysts for oxygen reduction reaction
Shufeng Wang, Dingling Yu, Xingquan He
Department of Chemistry and Chemical Engineering, Changchun University of Science and Technology, Changchun 130022, P. R. China.
E-mail: hexingquan@hotmail.com

Fig. S1 TEM image of Fe3N at high magnification showing a single nanoparticle (a) and the corresponding elemental mapping of O (b),C (c),Fe (d) and N (e), respectively.

Fig. S2 High resolution N1s spectra of Fe3N/N–GA-800 (a) and Fe3N/N–GA-1000 (b).

Table S1 The content of pyridinic N, Fe-N, pyrrollic N, graphitic N and oxidized N of Fe3N/N–GA-800, Fe3N/N–GA-900 and Fe3N/N–GA-1000.
Sample	N
(at%)	Fe
(at%)	Pyridinic-N
(at%)	Fe-N
(at%)	Pyrrolic-N
(at%)	Graphitic-N
(at%)	Oxidized N  
(at%)	
Fe3N/N–GA-800	1.8	0.88	42.88	6.36	9.22	21.53	20.01	
Fe3N/N–GA-900	1.58	1.72	43.19	8.29	7.08	24.53	16.91	
Fe3N/N–GA-1000	0.69	0.97	41.90	7.66	8.14	23.98	18.32	

Sample	N
(at%)	Fe
(at%)	Pyridinic-N
(at%)	Fe-N
(at%)	Pyrrolic-N
(at%)	Graphitic-N
(at%)	Oxidized N  
(at%)	
Fe3N/N–GA-800	1.8	0.88	42.88	6.36	9.22	21.53	20.01	
Fe3N/N–GA-900	1.58	1.72	43.19	8.29	7.08	24.53	16.91	
Fe3N/N–GA-1000	0.69	0.97	41.90	7.66	8.14	23.98	18.32	

   
Fig. S3 (a) SEM images of leached Fe3N/N–GA-900. (b) LSV polarization curves of Fe3N/N–GA-900 with acid leaching and without acid leaching.

ORR Activity Calculations
The kinetic parameters (n and Jk) were analyzed by Koutecky-Levich (K-L) Eq 1 and 2 as follows:
                       (1)
                             (2)
Where J is the measured current density, JK and JL are the kinetic and diffusion limiting current densities, respectively, n is the overall number of electrons transferred, F is the Faraday constant, C0 is the bulk concentration of O2 dissolved in the electrolyte, D0 is the O2 diffusion coefficient,  is the kinematic viscosity of the electrolyte, K is the electron transfer rate constant, and ω is the angular velocity of the disk (ω = 2πN, N is the linear rotation speed). The constant 0.2 is adopted when the rotating speed is expressed in rpm.
An additional rotating ring disk electrode (RRDE) experiment can be used to estimate n and further verify the ORR pathways, in which peroxide species produced during the ORR process at the disk electrode can be detected by the ring electrode. The electron transfer number and the percentage of hydrogen peroxide species can be determined by the following equations:
                                      (3)
                               (4)
Where Id is the disk current, Ir is the ring current, and N is the current collection efficiency of the Pt ring.