Modifying nitrogen species of nitrogen-doped carbon nanotubes by thermal annealing to explore their role in the triiodide reduction reaction

Dye sensitized solar cells can convert solar energy into electricity. The counter electrode plays a critical role catalyzing the reduction of the redox electrolyte which transports electrons to the photo-anode. Nitrogen doped graphitic Carbon materials have great catalytic activity for the Iodide reduction reaction (IRR). However, several nitrogen species coexist and not all of them contribute equally to the IRR activity. Therefore, the need to correlate the nitrogen species proportions with the IRR activity of nitrogen doped carbon materials. It is challenging to vary the proportion of nitrogen species directly from synthesis parameters. Then, we make use of thermal treatments of nitrogen doped carbon nanotubes (CNx-CNTs) to modify the amount of nitrogen species to be able to compare and analyze their IRR activity. The thermal treatments resulted in the pyrrolic nitrogen disappearance and a considerable decrease of the pyridinic nitrogen, while enriching the quaternary nitrogen content of the samples. The best IRR performance was achieved for the sample enriched with quaternary nitrogen. Remarkably, the CNx-CNTs peak current density equate the platinum reference sample performance. Moreover, we incorporate the CNx-CNTs into a water based ink for potential applications in flexible counter electrodes printing, and its IRR activity is systematically explored. (C) 2020 Elsevier Ltd. All rights reserved.