Active sites-enriched carbon matrix enables efficient triiodide reduction in dye-sensitized solar cells: An understanding of the active centers

Understanding the activity origins of electrocatalysts for the triiodide (I₃ ^-) reduction is highly desirable in dye-sensitized solar cells (DSSCs). Herein, we report a robust strategy to craft nitrogen-doped carbon nanowires (NCWs) through combining oxidation polymerization from p-phenylenediamine with carbonization process. Owing to the abundant edges of the graphite microcrystals embedded in the NCWs and the incorporated N species, the NCWs synthesized at 700 °C exhibit a superior response to the I₃ ^- reduction in DSSCs with a high power conversion efficiency of 8.90%, outperforming the Pt reference (8.09%), and a high stability is also manifested. Theoretical calculations reveal that, of various doped N species within NCWs, the quaternary N species can significantly decrease the ionization energy and modulate the spin density distribution of carbon frameworks, thus promoting the electron transfer from the external circuit to the electrolyte. Natural population analysis further reveals that the active centers within the NCWs for the I₃ ^- reduction are those positively charged carbon atoms adjacent to the quaternary N. As such, this work will pave an avenue for rational design and engineering of inexpensive yet high-efficiency carbon electrocatalysts for the advanced energy applications.