Based On The Derivatization Of ZIF-67 To Synthesize Bimetal Sulfides And Their Application In Dye-Sensitized Solar Cells

Energy crisis and environmental pollution have aroused widespread concern.Taking advantage of renewable clean energy is one of the most effective methods to deal with these issues.As a new type of green energy,solar energy is inexhaustible.And its effective development and utilization are crucial for the adjustment of energy structure and the development of ecological environment.Among plenty of new solar cells,dye-sensitized solar cells(DSSCs)have good prospects for development because of the simple manufacturing process,relatively low production cost and high power conversion efficiency.The counter electrode,as one of the essential and crucial components of DSSCs,plays a key role in typical DSSCs devices.It is necessary for the counter electrode material to exhibit good conductivity and electrocatalytic performance for,I3-reduction reaction.As a traditional DSSCs counter electrode material,platinum is scarcity,high cost,and easy to be corroded by electrolytes,which lead to reduce the catalytic performance.All these reasons make DSSCs difficult to achieve the goal of industrialization.Therefore,finding non-platinum counter electrode materials with low cost and superior property is one of the mainstream directions of studying DSSCs.This article aims to synthesize the bimetallic sulfides for non-platinum counter electrode materials of DSSCs based on the derivatization of ZIF-67.Bimetallic sulfides show higher specific surface area,more catalytical active sites,and a synergistic catalytic effect,so that its catalytic property is improved.The main research contents are as follows:1.Co8FeS8/N-C dodecahedral nanocages(DNCs)via cation exchange for the application in DSSCsBimetal sulfides Co8FeS8/N-C DNCs were successfully prepared by ZIF-67 as a template through subsequent sulfidation and cation exchange strategy.Co8FeS8/N-C DNCs were applied as counter electrodes for dye-sensitized solar cells.Firstly,the feasibility of the cation exchange method was determined based on theoretical calculations.Secondly,the chemical structure and composition were analyzed by X-ray diffractometer,inductively coupled plasma spectrometer and X-ray photoelectron spectrometer.Transmission electron microscope and scanning electron microscope were used to characterize the morphology and crystallinity.The experimental results indicate that Co8FeS8/N-C DNCs show the smallest peak potential difference,the smallest interfacial transfer resistance,and the largest exchange current density Jo than those of Pt counter electrode and monometallic sulfide Co9S8/N-C counter electrode for the reduction of triiodide.The high crystallinity and large specific surface area of the Co8FeS8/N-C DNCs are favorable for the adsorption and catalysis of I3-.When Co8FeS8/N-C DNCs were applied as the counter electrode(CE)for the dye-sensitized solar cells,they achieved high power conversion efficiency(PCE)of 8.06%,which were better than Pt CE.2.The synthesis of bimetallic sulfide nanocages(CoxM1-x)9S8/N-C(M=Ni or Cu)and the applications in DSSCs and OERUsing ZIF-67 as the template,they were transformed into hollow dodecahedron Co9S8/N-C firstly.Then bimetallic sulfides((CoxM1-x)9S8/N-C,M=Ni or Cu)and their composites((CoxM1-x)9S8/M/N-C,M=Ni or Cu)were obtained by doping different ratio of Ni2+and Cu2+ into Co9S8/N-C via cation exchange.The doping methods and element distributions of the two metal ions were confirmed through multiple characterization.Bimetallic sulfides show the excellent electrocatalytic performance for triiodide reduction reaction and oxygen evolution reaction(OER)owing to favorable compositional features and well-designed architectures.It was found that the catalytic performance extremely related to the atom ratio of Co:M and the component.(Co0.75Ni0.25)9S8/N-C DNCs delivered the best electrocatalytic activity for the triiodide reduction reaction and the highest power conversion efficiency(8.84%)in dye-sensitized solar cells(DSSCs),which was much higher than Pt and other component materials.Furthermore,(Co0.64Ni0.36)9S8/Ni/N-C-1 DNCs as an OER catalyst exhibited excellent electrocatalytic property in the light of the low overpotential(326 mV)at the current density of 10 mA cm-2.3.Graphene oxide assisted enhancement of CosFeSs and(CoxNi1-x)9Ss for catalytic reduction of iodide and the application in DSSCsIn order to improve the catalytic property of bimetal sulfide as a CE material for DSSCs,Co8FeS8 and(CoxNi1-x)9S8,which have better performance,were compounded with graphene oxide(GO),respectively.Firstly,ZIF-67 was grown in situ on the surface of GO.Co9S8/GO was formed by sulfidation.Then Co8FeS8/GO and(CoxNi1-x)9S8/GO composites were prepared by cation exchange.The characterizations of the composite material display that ZIF-67 was evenly distributed on the flat of GO and transformed into hollow Co9S8 after sulfidation.The bimetal sulfides were strongly loaded on the surface of GO to form the composite nanomaterials by cation exchange.The catalytic activity for I3-reduction was studied by cyclic voltammetry,electrochemical impedance spectroscopy and Tafel polarization curve.The results indicate that the electrocatalytic property was improved by adding graphene oxide Compared with pure Co8FeS8 and(CoxNi1-x)9S8,the photoelectronic experimental results show that the photoelectric conversion efficiency of Co8FeS8/GO and(CoxN1-x)9S8/GO as DSSCs counter electrodes have improved,which reached 8.74%and 8.98%respectively Bimetallic sulfide/graphene oxide composites are of latent applied value on the replacement of Pt electrodes in DSSCs,which can reduce the manufacturing costs and improve photoelectric conversion efficiency of DSSCs.