Synthesis of lignite-based Ni/C composite with low-medium temperature pyrolysis method as an efficient Pt-free counter electrode for dye-sensitized solar cells

In order to obtain inexpensive Pt-free counter electrode materials for dye-sensitized solar cells and expand the application fields of low-rank coal, lignite-based Ni/C composite was prepared by low-medium temperature pyrolysis method using Huolinhe lignite as raw materials. The structure and chemical components of as-synthesized lignite-based Ni/C composite was characterized by XRD, FT-IR, TG, Raman, SEM, TEM, and XPS, and the electrocatalytic activity of lignite-based Ni/C composite counter electrode was investigated by cyclic voltammetric curve, electrochemical impedance spectrum, and Tafel polarization curve. It is found that the electrocatalytic activity of the lignite was improved after low-medium temperature pyrolysis and composited with Ni species to form lignite-based Ni/C composite, which helps to catalyze the reduction of electrolyte and thus improve the photoelectric conversion efficiency of the solar cells. The photoelectric conversion efficiency (eta) of the dye-sensitized solar cells based on the lignite-based Ni/C composite counter electrode was 3.42% (J(sc) = 11.49 mA cm(-2), V-oc = 0.75 V, FF = 0.40) significantly higher than that of the lignite counter electrode (eta = 0.20%, J(sc) = 3.16 mA cm(-2), V-oc = 0.72 V, FF = 0.09). This indicates that low-medium temperature pyrolysis and composition with Ni are an effective method to improve the photovoltaic performance of lignite-based counter electrode materials.