Preparation,Characterization And Catalytic Properties Of Tungsten-based Bimetal Compounds As Counter Electrodes In Dye-sensitized Solar Cells

As a new generation of photovoltaic technology,dye-sensitized solar cells（DSSCs）have the advantages of high theoretical photoelectric conversion efficiency（PCE）,wide source of raw materials,simple preparation process,low cost and environmental friendliness in comparison with traditional silicon solar cells.As an important part of DSSCs,the counter electrode（CE）collects electrons from the external circuit and catalyzes the reduction of I₃^-ions in the electrolyte.However,traditional Pt CE materials are expensive,have a limited source,and easily corroded by I^-/I₃^-electrolytes.These disadvantages restrict the commercial application of DSSCs.Therefore,exploring efficient and low-cost Pt-free catalysts as CE material is urgently needed.In this work,three tungsten（W）-based bimetal compounds（Fe WO₄,Co WO₄,and Ni WO₄）were successfully prepared by hydrothermal reaction combined with heat treatment.As CE materials,the electrocatalytic activities of Fe WO₄,Co WO₄,and Ni WO₄ were evaluated.The results show that Fe WO₄,Co WO₄,and Ni WO₄ have good catalytic activities and electrochemical stabilities in the I^-/I₃^-electrolyte,and their corresponding DSSCs yielded PCEs of 4.65%,4.46%,and 5.01%,respectively.Three composite materials comprising W-based bimetal compounds and biomass carbon（Fe WO₄/BC,Co WO₄/BC,and Ni WO₄/BC）were successfully prepared by hydrothermal reaction combined with heat treatment to further improve the electrochemical catalytic performance of electrode materials.The introduction of BC reduced the agglomeration and particle sizes of Fe WO₄,Co WO₄,and Ni WO₄ in the composite.A formation of a hexagonal flower-like nanostructure was observed in Co WO₄ when porous bio-based carbon was used as the structure-directing agent.After the introduction of the BC,Fe WO₄/BC,Co WO₄/BC,and Ni WO₄/BC CEs exhibited enhanced electrocatalytic activities,electrochemical stabilities,and reduced charge-transfer resistance（8.50Ωcm²,8.07Ωcm²,and 2.17Ωcm² for Fe WO₄/BC,Co WO₄/BC,and Ni WO₄/BC,respectively）;moreover,the PCEs of the corresponding DSSCs reached 5.38%,6.07%,and 7.08%,respectively.The PCE of the DSSC with Ni WO₄/BC CE was higher than that of the DSSC with Pt CE（6.46%）.This result was due to the synergistic catalytic effect between the W-based bimetal compound and the biomass carbon,indicating their potential to replace Pt as a DSSC counter electrode material.The catalytic properties of the W-based bimetallic compounds and their composites in Cu⁺/Cu²⁺electrolytes were further explored.The electrochemical performance tests showed that the catalytic activities of Fe WO₄/BC,Co WO₄/BC,and Ni WO₄/BC were better than those of Fe WO₄,Co WO₄,and Ni WO₄,and were similar to those of the Pt electrode.DSSCs assembled by Fe WO₄/BC,Co WO₄/BC,and Ni WO₄/BC electrodes obtained PCEs of 2.06%,2.51%and 2.53%,respectively,in the Cu⁺/Cu²⁺electrolyte and Y123 dye system.These values were close to the PCE（2.98%）of the DSSC with Pt electrode under the same conditions.