Effect of Annealing Temperatures on Oxygen Reduction Reaction and Structure of Nitrogen and Sulfur Co-Doped Mesoporous Carbon Prepared from Polyquaternium-46
Authors: Qiao Jinli 
Published: February 2020

Mesoporous carbon materials have been used for numerous applications such as adsorption1, separation2, supercapacitor3 and oxygen reduction reaction (ORR)4 due to their preeminent textural characteristics, high surface area, mechanical stability and mesoporous structure. The properties of mesoporous carbon materials base on not only the sizes and location of the pore, but the heteroatoms doped into the carbon framework. Abundant experimental studies have certified that chemical doping of mesoporous carbon with foreign atoms, especially nitrogen and sulfur, can improve its electrochemical properties of ORR, as well as lead to new functions5. It is believed that the quantity of N-doped and S-doped in carbon will be vastly different if it was annealed at various reaction temperatures6. Herein, we use N and S co-doped mesoporous carbon which is prepared by Polyquaternium as a starting material to investigate the reaction in N2at various temperatures.
The nitrogen and sulfur co-doped mesoporouss carbon electrode materials (Fe-LH) were prepared by homogeneously dispersion of polyquaternium-46 (Luviquat- HOLD) and ferrous chloride (FeCl2·4H2O) precursors onto the surface of silica (which was firstly dispersed in hydrochloric acid solution by ultrasonication, the metal loading with respect to silica is 15 wt.% ). After dried overnight, the resulting solid was ground to a fine powder, and then calcined at temperatures from 700, 800 and 900℃ to form the different structure for 1h in nitrogen atmosphere. The excess amount of sodium hydroxide (NaOH) was added to vacate the silica and the resulting powder was acid-leached using 0.5 M H2SO4at 80℃ to remove the unreacted metallic Fe. Then, the catalytic graphitization of the impregnated carbon was subjected heat treatment at 700 to 900℃ for 1h pyrolyzation time again.
Besed on these method, we obain the mesoporous carbon with high porosity, and the electrocatalytic activity on the it was investigated using cyclic voltammetry (CV) and linear sweep voltammetry (LSV) employing rotating ring-disk electrode (RRDE)
Fig. 1 shows CV responses of Fe-LH-800℃ in N2/O2 saturated 0.1 M KOH solution. In the case of a N2-saturated solution, the cyclic voltammogram only presents a featureless quasi-rectangular trace. However, when O2 is introduced into the solution, a distinct ORR response with the peak potential (Ep) at 0.82 V vs. RHE, and the peak current density (Ip) of 3.61 mA cm-2can be clearly observed, indicating that this Fe-LH-800℃ catalyst has a profound catalytic ORR activity. Fig. 2 shows the polarization curves of the Fe-LH-700℃, Fe-LH-800℃ and Fe-LH-900℃ catalysts. It can be seen that the high activity of Fe-LH-800℃ for oxygen reduction was clearly demonstrated by onset potential of 0.88V, half-wave potential of 0.83V, which are positively shifted more than 93 and 36 mV, respectively, compared to Fe-LH-700℃ and Fe-LH-900℃.
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Figure 1