A novel porous three dimensional (3D) hierarchical graphene-beaded carbon nanofibers with incorporated Ni nanoparticles (G/CNFs-Ni) were used for the first time as cost-effective counter electrode for dye-sensitized solar cells (DSCs). G/CNFs-Ni was synthesized by electrospinning G/PAN/Ni(AcAc)2 precursor nanofibers, followed by carbonization and activation. The introduction of graphene nanosheets and Ni nanoparticles in CNF networks significantly increased the cells' stability and decreased the charge-transfer resistance at the interface between electrolyte and counter electrode, leading to the high electrocatalytic activity/efficiency for triiodide reduction. The G/CNFs-Ni composite counter electrodes possessed larger capacitance than that of Pt counter electrodes due to larger specific surface area, leading to significantly higher electrocatalytic activity/efficiency for triiodide reduction at the interface between electrolyte and counter electrode. The dye-sensitized solar cells (DSCs) fabricated using G/CNF-Ni composite as counter electrodes were tested at 100 mW/cm 2 AM 1.5 illumination. The G/CNFs-Ni composite exhibited an overall power conversion efficiency of 7.14 % as compared to 7.59 % for reference platinum (Pt) counter electrodes.

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5Graphene-embedded carbon nanofibers (GCNFs) were developed as a new counter electrode nanomaterial for higher efficiency dye-sensitized solar cells (DSCs). GCNFs were produced by electrospinning polyacrylonitrile (PAN) with graphene nanoplatelets followed by stabilization and carbonization. GCNFs decorated with surface-attached platinum nanoneedles (GCNFs-PtNNs) were 10 subsequently prepared by redox reaction and then deposited onto fluorine doped tin oxide (FTO) glass to make counter electrode for DSCs. Graphene inside carbon nanofibers and Pt nanoneedles on the surface demonstrated synergistic effects on improving DSC performance. Compared to DSCs with conventional planar Pt counter electrode, the DSCs with GCNFs-PtNNs significantly improved the energy conversion efficiency from ~ 8.63% to ~ 9.70% using a mask under AM1.5 illumination. This is the highest 15 conversion efficiency so far with carbon nanofiber based counter electrode. 65 2. Experimental Materials Polyacryonitrile (PAN), N, N-dimethylformamide (DMF), chloroplatinic acid (H 2 PtCl 6 ), formic acid (HCOOH), TiCl 4 liquid (≥ 99.0%), and Titanium diisopropoxide bis(acetylacetonate) (75 70 wt.% in 2-propanol) were purchased from Sigma-Aldrich Corporation (St. Louis, MO). Graphene nanoplatelet particles (C-750) were purchased from XG Sciences, Inc. (Lansing, MI). Fluorine doped tin oxide (FTO) substrates were ordered from Hartford Glasses. Nanocrystalline TiO 2 (Ti-Nanoxide HT/SP), 75scattering TiO 2 (Ti-Nanooxide R/SP), and N719 dye (Ruthenizer 535-bisTBA) were purchased from Solaronix. All materials were used as received except that TiCl 4 was diluted in deionized water (DI) to prepare a 40 mM aqueous solution. Preparation of TiO 2 photoanode 80FTO substrates were cleaned with detergent, deionized (DI) water, acetone, and 2-propanol in an ultrasonic bath for 10 min each. The cleaned FTO was first immersed in 40 mM TiCl 4 aqueous solution at 70 °C for 30 min, then cleaned with DI water DSCs, 15.2 mA·cm -2 for GCNFs based DSCs, and 18.56 mA·cm -2 for GCNFs-PtNNs based DSCs. These values were very close to corresponding values from J-V analysis and further confirmed measurements of power conversion efficiency.