Study on Electrocatalysis of Single-Atom Catalysts in the Counter Electrodes of Dye-Sensitized Solar Cells

Author:Liang Su Xia

Supervisor:hao ce shi yan tao


Degree Year:2019





It is of great significance to study single atom catalysts and their electrocatalytic behavior,which not only dramaticly reduces the use of precious metals,but also greatly promotes the design of electrocatalysts at atomic/molecular scale and further understanding of the essence of electrocatalysis.Dye-sensitized solar cells(DSSCs)are representative in the third generation of noval thin-film solar cells.It is the only known photovoltaic device using electrolyte.Iodine electrolyte(the redox pair is I-/I3-)is the most effective and widely used electrolyte.The oxidizing substance(I3-)undergoes a reduction reaction in the CEs of DSSCs,which has remarkable effect on the photovoltaic performance of the whole DSSCs device.This desertation focuses on the following key scientific issues:the electrocatalysis of counter electrodes in DSSCs and interfacial charge exchange in CEs,selects specific supported single atom catalysts as the research objects,and explores the structure-activity relationship between the composition and electronic structure of the SACs.Accordingly,three kinds of SACs were designed and prepared.Their electrochemical properties were systematically characterized and compared with the traditional catalytic materials.This study investigated the effects of sinlge atom on catalytic properties of the SACs and emphasized the relationship between the microstructure and catalytic activity of the materials.Firstly,we synthesized a novel single atom catalyst-Ti1/rGO by wetness adsorption method,using graphite oxide and organic metal titanium salt as raw materials,by means of the strong interaction between titanium atoms and oxygen-containing functional groups on the surface of graphite oxide.The HAADF-STEM characterization results showed that the titanium in the sample was monoatomic dispered.In order to further clarify the chemical structure of Ti1/rGO,a series of characterization were performed.The bonding structure of single atom Ti was confirmed by X-ray absorption fine structure spectroscopy.Ti atom was bound to the support through Ti-O-C bond.The structure of the prepared sample was analyzed and its catalytic activity was explored from the perspective of theoretical simulation.Compared with rGO,the ionization potential of Ti1/rGO decreased,the electron donation ability increased,and the catalytic activity of Ti1/rGO for IRR increased.Ti1/rGO as counter electrode(CE)materials in DSSCs,the photoelectric conversion efficiency of 8.29%was obtained,which was 37%higher than that of rGO.The results of electrochemical performance test showed that the catalytic activity of Ti1/rGO was significantly higher than that of rGO.The experimental results were consistent with the theoretical predictions.Secondly,we demonstrated the use of Pt1/FeOx as a counter electrode material in DSSCs.The IRR catalytic activity of the catalyst and its influence on the photoelectric properties of DSSCs were systematically studied from both experimental and theoretical approaches.The experimental results showed that the IRR catalytic activity of bare FeOx was very unsatisfactory.When 0.02wt%single atom Pt anchored on the bare FeOx,its catalytic activity was significantly enhanced,accordingly,the photoelectric conversion efficiency of DSSCs was dramatically improved.On the basis of the above experimental studies,the role of Pt single atoms in SACs was further analyzed theoretically.As indicated by the interaction between I atom and the O3-terminated Pti/Fe2O3(001)surface,charge transfer occured mainly between I atom and the surface Pt atom.After the anchoring of single atom Pt,on the one hand,the ionization potential decreased and the electron donation ability increased;on the other hand,the electronic stales became much more concentrated and density of the occupied states became higher around the Fermi energy level.This study elucidated the reason why atomically dispersed Pt on FeOx surface had high catalytic activity in IRR.Thirdly,another single atom catalyst Pt1/MnO was synthesized.As a counter electrode material in DSSCs,we systematically studied the IRR catalytic performance of Pt1/MnO by different electrochemical methods,and tested the photovoltaic performance of DSSCs devices assembled by Pt1/MnO CEs.Based on the above experimental study,the relationship between microstructure of Pt1/MnO and its catalytic activity was analyzed by DFT simulation calculation.Compared with MnO,Pt1/MnO had a lower work function,meaning that Pt1/MnO had a relative higher electron-donating ability.The DOS results indicated that the electronic states of Pt1/MnO(100)around the Fermi energy level became much more concentrated and density of the occupied states became much higher,after single atom Pt anchored on MnO(100)surface.By comparing the adsorption energy of transition metal atoms anchored on Mn vacancy of MnO(100)surface and its own average atomic binding energy,with Mn vacancy of Mn(100)surface as anchoring sites,it was predicted that the following stable single atom catalysts might be obtained:Yi/MnO,Zri/MnO,Lai/MnO and Hfi/MnO.