Synergistic effect of molybdenum nitride and carbon nanotubes on electrocatalysis for dye-sensitized solar cells

Abstract

As a counter electrode for dye-sensitized solar cells (DSSCs), MoN presents a high intrinsic electrocatalytic activity for the reduction of triiodide ions. However, the photovoltaic performance of DSSCs with a MoN counter electrode is hindered by the large diffusion impedance of the MoN electrode. In response to this problem, a MoN–carbon nanotube (CNT) composite is prepared by nitridation of the precursor MoO₂–CNTs, fabricated via a hydrothermal reaction of ammonium molybdate and carboxyl-functionalized CNTs. In the composite, MoN nanoparticles are well and stably dispersed on the surface of the CNTs, with a particle size of several tens of nanometers. Employing the composite as a counter electrode, the DSSC shows an energy conversion efficiency of 6.74%, which is much higher than that (5.57%) of the DSSC using pure MoN nanoparticles. The improvement is mainly attributed to a synergistic effect between the MoN nanoparticles and CNTs on ion diffusion and electrocatalysis. Electrochemical impedance spectra (EIS) indicate that the MoN–CNTs electrode has a lower ion diffusion impedance. It is believed that the smaller size of the MoN nanoparticles and the abundant porous structure in the MoN–CNTs composite are able to shorten the ion diffusion path and improve ion diffusion flux.