Enhanced Synergetic Catalytic Effect of Mo2C/NCNTs@Co Heterostructures in Dye-Sensitized Solar Cells: Fine-Tuned Energy Level Alignment and Efficient Charge Transfer Behavior.

A highly active and stable electrocatalyst with the novel heterostructure of Co-embedded and N-doped carbon nanotubes supported Mo2C nanoparticles (Mo2C/NCNTs@Co) is creatively constructed by adopting the one-step metal catalyzed carbonization-nitridation strategy. Systematic characterizations and density functional theory (DFT) calculations reveal the advanced structural and electronic properties of Mo2C/NCNTs@Co heterostructure, in which the Co-embedded and N-doped CNTs with tunable diameters present electron-donating effect and the work function is correspondingly regulated from 4.91 to 4.52 eV, and the size-controlled Mo2C nanoparticles exhibit Pt-like 4d electronic structure and the well matched work function (4.85 eV) with I^-/I_(3 )^- redox couples (4.90 eV). As a result, the conductive NCNTs@Co substrate with fine-tuned energy level alignment accelerates the electron transportation and the electron migration from NCNTs@Co to Mo2C, and the active Mo2C shows high affinity for I_(3 )^- adsorption and high charge-transfer ability for I_(3 )^- reduction, which reach a decent synergetic catalytic effect in Mo2C/NCNTs@Co heterostructure. The DSSC with Mo2C/NCNTs@Co CE achieves a high power conversion efficiency of 8.82% and exceptional long-term stability with a remnant efficiency of 7.95% after 200 h of illumination, superior to those of Pt-based cell. Furthermore, the possible synergistic catalytic mechanism towards I_(3 )^- reduction is proposed based on the structure-activity correlation and DFT calculations. The advanced heterostructure engineering and electronic modulation provide a new design principle to develop the efficient, stable and economic hybrid catalysts in relevant electrocatalytic fields.