Hierarchical nickel sulfide/carbon nanotube nanocomposite as a catalytic material toward triiodine reduction in dye-sensitized solar cells

In this study, Ni3S2 nanoparticles are successfully decorated on the backbone of conductive multi-walled carbon nanotubes (denoted as Ni3S2/MWCNT-NC) via a facile glucose-assisted hydrothermal method and employed as a counter electrode (CE) in dye-sensitized solar cells (DSCs). It is noteworthy that the use of glucose in the hydrothermal reaction plays a crucial role in the formation of the nanocomposite structure. Nevertheless, a thick layer of amorphous carbon derived from the hydrothermal carbonization of glucose covers Ni3S2 nanoparticle surface, and thus may inhibit the contact of active sites in Ni3S2 nanoparticles with electrolyte. It is found that the partial amorphous carbon on Ni3S2/MWCNT-NC can be effectively removed after annealing at 400 °C in a nitrogen atmosphere, which further increases the active sites of Ni3S2 nanoparticles on MWCNTs and therefore improves the electrocatalytic activity of the Ni3S2/MWCNT-NC CE. As a result, the DSC with the Ni3S2/MWCNT-NC CE yields a cell efficiency of 6.87%, which is higher than those of DSCs based on the Ni3S2 CE (5.77%) and MWCNT CE (3.76%). Because the Ni3S2/MWCNT-NC CE based DSC shows a comparable photovoltaic performance to the DSC using the Pt CE (7.24%), Ni3S2/MWCNT-NC CE may serve as a promising alternative to Pt CE for DSCs. [Display omitted] •Ni3S2/MWCNT-NC was synthesized via a facile glucose-assisted hydrothermal method.•Annealed Ni3S2/MWCNT-NC CE showed improved catalytic activity for I3− reduction.•Ni3S2 and conductive MWCNTs imparted high catalytic activity and stability to the catalyst.•The DSC with the annealed Ni3S2/MWCNT-NC CE reached an efficiency of 6.87%.•Ni3S2/MWCNT-NC CE served as an inexpensive and promising alternative to Pt CE for DSCs.