Electrospun carbon nano-felt derived from alkali lignin for cost-effective counter electrodes of dye-sensitized solar cells

In this study, freestanding and mechanically flexible nano-felt consisting of electrospun carbon nanofibers (ECNFs) derived from alkali lignin with a BET specific surface area of ∼583 cm² g^-1 and average pore size of ∼3.5 nm was prepared and then surface-deposited with Pt nanoparticles (Pt NPs). Both nano-felts of ECNFs and ECNFs-Pt were studied as cost-effective counter electrodes of dye-sensitized solar cells (DSSCs). The energy-dispersive X-ray spectroscopy (EDS) results showed that the amount of Pt NPs in ECNFs-Pt nano-felt was ∼9.9 wt%, and the scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) results indicated that the Pt NPs with small sizes in the range of 2-20 nm were randomly distributed on the surface of ECNFs. The electrochemical impedance spectroscopy (EIS) tests revealed that the ECNFs-based counter electrode had low charge transfer resistance (R_ct = 1.94 Ω cm²), and the R_ct value was reduced to 1.2 Ω cm² upon surface-deposition of Pt NPs. The prototype DSSCs based on ECNFs and ECNFs-Pt counter electrodes exhibited comparable performances to the DSSC based on a conventional Pt counter electrode in terms of short circuit density (J_sc), open circuit voltage (V_oc), fill factor (FF), and energy conversion efficiency (η).