Hierarchical carbon nanofibers/carbon nanotubes/NiCo nanocomposites as novel highly effective counter electrode for dye-sensitized solar cells: A structure-electrocatalytic activity relationship study

Herein, we propose novel, highly effective Pt-free counter electrode (CE) material for dye-sensitized solar cells (DSSC) based on the hierarchical carbon nanofibers/carbon nanotubes/NiCo (eCNF/CNT/NiCoNP) ternary nanocomposites. The materials were obtained by combining the electrospinning technique and CCVD synthesis of carbon nanotubes directly on the surface of eCNF. By using various conditions of the CNT growth, it was possible to obtain series of nanocomposites differing with their morphology, surface chemistry, and structural ordering. The conducted studies unraveled significant correlations between the disordering of the nanocomposites, and their electrocatalytic activity towards reduction of I-3(.). The investigation methods included i.a. SEM, TEM, XPS, UPS, EDS, XRD, SAED, CV, EIS and J-V characterizations. The counter electrodes based on the nanocomposite synthetized at the lowest CCVD temperature of 700 degrees C exhibited remarkable catalytical activity as evidenced by very low charge transfer resistance of 0.93 O cm(2). Based on the obtained data, we propose new, alternative interpretation of the additional minor arc appearing at the high-frequency region of EIS Nyquist spectra of carbon based-CE. The DSSC with eCNF/CNT/NiCoNP-electrodes were characterized by efficiencies up to 7.08% (avg.eta = 6.95%), which was higher than for Pt-based devices (avg.eta = 6.80%), thus demonstrating excellent performance of prepared CE. Our results confirm that the eCNF/CNT/NiCoNP nanocomposite material is a promising low-cost CE alternative for DSSC.

Automated summary

In this study, a novel Pt-free counter electrode (CE) material, based on hierarchical carbon nanofibers/carbon nanotubes/NiCo (eCNF/CNT/NiCoNP) ternary nanocomposites, was proposed for dye-sensitized solar cells (DSSC). The nanocomposites were obtained through a combination of the electrospinning technique and CCVD synthesis. The morphology, surface chemistry, and structural ordering of the nanocomposites were found to have significant correlations with their electrocatalytic activity. The DSSC with eCNF/CNT/NiCoNP-electrodes exhibited higher efficiencies compared to Pt-based devices, demonstrating the excellent performance of the prepared CE.