Synthesis of bimodal mesoporous carbon with embedded nickel nanoparticles through pyrolysis of nickel-organic framework as a counter-electrode catalyst for dye-sensitized solar cells

Bimodal mesoporous carbon with embedded Ni nanoparticles (BMCNi) was prepared by thermal pyrolysis of nickel-organic framework (NiOF) in nitrogen environment followed by acid treatment. The coordination complex of NiOF enabled the formation of small mesopores (3.6 nm) during pyrolysis. The thermal decomposition and acid treatment generated large mesopores (23.6 nm). The small mesopores contributed to high surface area and the large mesopores speeded up the transport of electrolyte species. Fluorine-doped tin oxide electrode with attached BMCNi catalyst possessed good electrocatalytic performance for I−/I3− couple compared with bimodal mesoporous carbon (BMC) only, owing to its high current peak and small voltage separation between anodic and cathodic peaks in cyclic voltammetry test. Ni nanoparticles embedded in BMC could provide electrical conductivity and extra active sites for facilitating the redox reaction. BMC with high surface area acted as not only a catalyst, but also a protective matrix to lessen the corrosion of Ni nanoparticles in I−/I3− electrolyte, leading to an improved electrochemical stability. Consequently, the dye-sensitized solar cell employing BMCNi counter electrode could reach a cell efficiency of 8.6%, which is higher than that using Pt (8.4%).