The effect of carbonization temperature on the electrocatalytic performance of nitrogen-doped porous carbon as counter electrode of dye-sensitized solar cells

Nitrogen-doped porous carbons (NPC) prepared by direct carbonization of nitrogen-containing polymer were investigated as the counter electrode of dye-sensitized solar cells. The effect of carbonization temperature on the electrocatalytic performance of NPC electrode was discussed. The nitrogen content reasonably decreased with the increase of carbonization temperature for NPC samples. However, the electrocatalytic activity of NPC electrode did not follow the same trend. As carbonization temperature increased from 700 to 800 °C, the charge-transfer resistance of NPC electrode decreased from 8.07 to 1.77 Ω cm². With further increasing carbonization temperature from 800 to 900 °C, the charge-transfer resistance of NPC electrode increased from 1.77 to 5.08 Ω cm². X-ray photoelectron spectroscopy analysis identified three kinds of nitrogen in as-prepared NPC, including pyridinic, pyrrolic, and quaternary nitrogen. With the increase of carbonization temperature, the content of pyridinic and pyrrolic nitrogen decreased, while the content of quaternary nitrogen increased. Pyridinic and pyrrolic nitrogen could create the electrocatalytic active sites in NPC, while quaternary nitrogen could improve the electron transfer through NPC. Therefore, the proper ratio among different nitrogen states has a significant effect on the electrolcatalytic activity of NPC. The NPC prepared at moderate carbonization temperature of 800 °C exhibited a superior electrolcatalytic activity because it possessed both relatively higher content of pyridinic nitrogen and higher content of quaternary nitrogen.