Preparation And Application Of Novel Composite Transition Metal Sulfide Catalyst Materials

Transition metal sulfides?TMSs?have attracted widespread attention due to their good physicochemical properties in recent years.The researchers found that transition metal sulfides have excellent catalytic activity,but their conductivity is poor.As a new carbon material,the carbon nanofibers have good electrical conductivity.In this paper,the composite material of transition metal sulfides and carbon fibers were prepared,which could combine the two advantages together,so that the composite materials have both the catalytic performance of the transition metal sulfides and the electrial conductivity of the carbon fibers.As an important part of dye-sensitized solar cells?DSSCs?,the counter electrode plays the role of collecting external circuit electrons and catalytic redution of redox couples in the catalytic reduction electrolyte.Transition metal sulfide composites have very high research significance and practical application value in dye-sensitized solar cells.In order to expand the research and application of transition metal sulfide materials,we selected MoS₂/carbon nanofibers?MoS₂/CNFs?,NiCo₂S₄/carbon nanofibers?NiCo₂S₄/CNFs?and NiMoS₃/carbon nanofibers?NiMoS₃/CNFs?for research,and described the preparation method and experiment results of each materials in detail.The results are as follows:?1?High-density“flower like”MoS₂/CNFs composites were prepared by electrospinning and one-step hydrothermal synthesis.The composites were used as catalysts in DSSCs.As a typical two-dimensional layered material,flower-like MoS₂ consists of two layers of sulfur atoms interposed with a layer of molybdenum atoms.It has a considerable number of Mo-S facets,high catalytic activity and large specific surface area.Scanning electron microscopy?SEM?results show that the flower-like MoS₂ nanosheets have a thickness of about 10-30 nm and are uniformly grown on the surface of carbon fibers.The composites?MoS₂/CNFs?combined the high conductivity of carbon nanofibers with the high catalysis of MoS₂materials.It was applied to the counter electrode of the dye-sensitized solar cells,and has an excellent photoelectric conversion efficiency?PCE?of 8.46%,the short-circuit current(J_sc)was 15.64%,which is higher than the Pt counter electrode?7.65%?under the same conditions.The Cyclic voltammetry?CV?and Tafel tests showed that the electrodes prepared by the MoS₂/CNFs composites have higher exchange current density?J₀?,limiting current density(J_lim)and smaller peak-to-peak(E_pp)value than pure CNFs and Pt electrodes.A series of morphological characterization and electrochemical test results show that the MoS₂/CNFs composite was a good counter catalytic material for electrode.?2?The carbon nanofiber-loaded bimetallic transition metal sulfide?NiCo₂S₄/CNFs?was obtained by combining electrospinning technology and hydrothermal method,and the composite material can combined the catalytic activity of the NiCo₂S₄ with the conductivity of the carbon nanofibers.In the composite system,NiCo₂S₄ was uniformly distributed and supported on the surface of carbon nanofibers?CNFs?.Compared with the single metal sulfides NiS and CoS,NiCo₂S₄ has more elemental valence states,which could be effectively achieved by the synergy between metal cations and increased the electrochemical reactivity of the electrode material to provide more oxidation active sites for the electrolyte.The prepared NiCo₂S₄/CNFs composites exhibited better catalytic activity on the electrode.A series of electrochemical measurements showed that NiCo₂S₄/CNFs possess excellent photoelectric conversion efficiency?PCE?9.0%and stability in iodine electrolyte.?3?Ni and Mo bimetallic doped transition metal NiMoS₄/CNFs composite counter electrode materials were successfully prepared by a simple one-step electrospinning and vulcanization method.Compared with single metal,bimetallic sulfide has a synergistic effect on the two metals,which greatly improves the electrical conductivity of the material while retaining the good redox characteristics of the material.As a chalcogen compound,NiMoS₃has more active sites and higher conductivity that greatly enhances the electron transport rate.The unique pore-like rough surface of the carbon fibers were combined with the catalytic activity of the NiMoS₃ particles.In this paper,we investigated the photoelectric conversion efficiency of DSSCs with NiMoS₃/CNFs counter electrode,obtained the PCE of 8.7%which was higher than that of the precious metal Pt?7.53%?.In order to improve the catalytic performance of the electrodes,highly stable transition metal sulfides?TMSs?undoubtedly provide another path for the development of electrode materials.This study confirmed that the transition metal NiMoS₃/CNFs composites have a significant effect on the reduction of I₃^-and the improvement of DSSCs performance,providing a new design idea for the development of efficient and low-cost DSSCs.