Deciphering the Electrocatalytic Activity of Nitrogen-Doped Carbon Embedded with Cobalt Nanoparticles and the Reaction Mechanism of Triiodide Reduction in Dye-Sensitized Solar Cells

The electrocatalytic activity of carbon materials for triiodide (I<sub>3</sub><sup>–</sup>) reduction has spurred the development of low-cost electrocatalysts as an alternative to platinum in dye-sensitized solar cells. While many catalytic aspects of nitrogen-doped carbons have been unveiled in recent years, not all underlying factors that dictate their electrocatalytic activity have been fully considered; the current understanding of the electrocatalytic activity of nitrogen-doped carbons is limited. In addition, the synergistic effect of metal nanoparticles embedded in nitrogen-doped carbon, which was recently demonstrated as a facile way to boost the electrocatalytic activity of carbon, remains elusive. This work sheds light on these unknown aspects of carbon’s electrocatalytic activity by carrying out a systematic investigation of nitrogen-doped carbon with incorporated cobalt nanoparticles. Furthermore, the generally accepted mechanism of the I<sub>3</sub><sup>–</sup> reduction reaction (IRR) is re-evaluated in this work with the aid of density functional theory calculations and in-depth electrochemical analysis. A new insight into this mechanism, which suggests that there is another possible reaction pathway available for the IRR on carbon, is provided.