Theoretical and Experimental Insights into the Effects of Oxygen-Containing Species within CNTs toward Triiodide Reduction

Heteroatom-doped micro-/nanostructured carbon materials feature unique superiorities for replacement of noble metal Pt counter electrode (CE) in dye-sensitized solar cells. Nevertheless, the effects of oxygen-containing species on/within carbon matrix on its electrocatalytic activity are seldom considered and concerned, is be hindered by a trade off between oxygen defects and conductivity. Herein, we report on the synthesis of activated carbon nanotubes (P-CNTs) with abundant active edge sites and oxygen species for simultaneous achieving the activation of sidewalls and open ends. Also, the positive effects of oxygen species are decoupled experimentally combined with theoretical analysis. With P-CNTs as the CE of DSSCs, the device delivers a high power conversion efficiency of 8.35% and an outstanding electrochemical stability, outperforming that of Pt reference (8.04%). The density functional theory calculation reveals that compared with the carboxylic groups, the hydroxyl groups and carbonyl groups on the surface of CNTs can greatly reduce the ionization energy of reaction and accelerate the electron transfer from external circuit to triiodide, and are thus responsible for an enhanced electrocatalytic performance. This work demonstrates that a certain amount of oxygen atoms within carbon materials is indispensable for the improvement in the reactivity of the triiodide.