10.1016/j.nanoen.2015.02.025
High-density iron nanoparticles encapsulated within nitrogen-doped carbon nanoshell as efficient oxygen electrocatalyst for zinc-air battery

Dicyandiamide and ammonium ferric citrate are used as pyrolysis precursors. 

In a typical experiment, 8 g of dicyandiamide (C2H4N4, Alfa Aesar, denoted as DCDA) and 1 g of ammonium ferric citrate (C6H11FeNO7, J&K Chemical Ltd., denoted as AFC) were dissolved in 100 mL of de-ionized water. The solution was continuously stirred and dried at 80 degC. The obtained mixture was placed in a quartz tube of a horizontal furnace. The pyrolysis of the mixture was performed in Ar atmosphere at a flow rate of 50 mL min-1. The furnace was heated to the target temperature at a rate of 10 degC min-1 and kept at the target temperature for 2 h, then cooled to room temperature. Then the samples were leached in 0.5 M HClO4 solution at 80 degC for 8 h to remove unstable iron species, and washed thoroughly with de-ionized water. Finally, the samples were dried at 60 degC in an oven. For highlighting the role of iron precursor, ferric chloride was used instead of AFC, and the mixture of DCDA and ferric chloride was pyrolyzed at 700 degC, followed by acid-leaching and washing, which is denoted as D-FC-700. The weight ratio of DCDA to iron was kept identical in the DCDA-AFC and DCDA-FeCl3 mixtures.
dicyandiamide (C2H4N4
dissolved
8 g
g
ammonium ferric citrate (C6H11FeNO7
dissolved
1 g
g
de-ionized water
100 mL
mL
solution
dried
80 degC
degC
pyrolysis of the mixture
flow rate
50 mL min-1
mL min-1
furnace
rate
10 degC min-1
degC min-1
furnace
kept at the target temperature
2 h
h
HClO4 solution
0.5 M
M
samples
leached
80 degC
degC
samples
leached
8 h
h
samples
dried
60 degC
degC
mixture of DCDA and ferric chloride
pyrolyzed
700 degC
degC