Preparation, Characterization And Catalytic Performance Of Niobium-based Bimetallic Compounds As Counter Electrodes In Dye-sensitized Solar Cells

Dye-sensitized solar cells（DSSCs）,which are considered forerunners of the third generation of photovoltaic devices and represent the frontier of solar cell technology,have attracted extensive research attention due to their many advantages,which include low preparation cost,extensive material resources,high photoelectric conversion efficiency（PCE）,and environment friendliness.Counter electrodes are a key component of DSSCs.The catalytic performance,electrical conductivity,and electrochemical stability of the electrode material largely determine the photovoltaic performance of solar cells.Therefore,developing new electrode materials with high catalytic performance,low preparation cost,and widely available material resources is of great significance.（1）Three types of Nb-based bimetallic compunds,namely,Co Nb₂O₆,Ni Nb₂O₆,and Zn Nb₂O₆,were prepared via the hydrothermal method followed by annealing;the compounds exhibited good crystallinity,high phase purity,and a uniform particle size distribution.The as-prepared materials were applied as counter-electrode catalysts in DSSCs,and their electrochemical properties,photovoltaic performance,and electrochemical stability were systematically characterized.Results showed that Co Nb₂O₆,Ni Nb₂O₆,and Zn Nb₂O₆ possess good catalytic activity and electrochemical stability in I^-/I₃^-electrolyte,and the corresponding DSSCs showed PCEs of 5.89%,6.14%,and 6.65%,respectively.（2）Aloe peel,a biomass waste,was used as a carbon source to prepare bio-based porous carbon;this carbon was introduced to Nb-based bimetallic compounds to successfully prepare Nb-based composites,namely,Co Nb₂O₆/BPC,Ni Nb₂O₆/BPC,and Zn Nb₂O₆/BPC.Introduction of the porous carbon significantly improved the agglomeration of the Nb-based bimetallic nanoparticles and increased their dispersibility.The synergistic effect between the Nb-based bimetallic compounds and BPC endowed the corresponding composites with obvious improvements in electron transport ability and catalytic activity compared with those of pristine bimetallic compounds.The composites achieved optimal R_ct（9.80Ωcm²,5.98ΩΩcm² and 3.34cm²）and presented excellent catalytic activity and electrochemical stability.The PCEs of Co Nb₂O₆/BPC and Ni Nb₂O₆/BPC-based DSSCs reached 5.98%and 6.36%,respectively.Interestingly,the Zn Nb₂O₆/BPC-based DSSC achieved a PCE of 8.83%,which is higher than that of a Pt-based cell（PCE,7.12%）.（3）Based on the two most important functions of the counter electrode,collecting the external circuit electrons and catalyzing I₃^-reduction,the first-principle density functional theory has been performed to anylysize the underlying catalytic mechanism of Zn Nb₂O₆ catalyst from two aspect,band gap and surface adsoption.The results indicate that zero band gap of surface metal atoms and the chemical adsorption of I₃^-on the surface are more conducive to the electron transport and catalytic reaction;the strong interaction between the surface metal atoms and the I atom result in the I-I bond to elongate,which promotes the catalytic reaction.（4）The catalytic properties of Nb-based bimetallic compounds and their composites were further explored in a reaction system containing Cu⁺/Cu²⁺electrolyte and Y123 dye.Electrochemical performance tests showed that the catalytic activities of Co Nb₂O₆/BPC,Ni Nb₂O₆/BPC,and Zn Nb₂O₆/BPC are better than those of their Nb-based bimetallic compounds and similar to that of Pt.In photovoltaic performance tests,DSSCs assembled with Co Nb₂O₆/BPC,Ni Nb₂O₆/BPC,and Zn Nb₂O₆/BPC electrodes achieved PCEs of 1.78%,2.11%,and 2.33%,respectively,in the Cu⁺/Cu²⁺electrolyte and Y123 dye system;these PCEs are similar to that of a DSSC assembled with a Pt electrode under the same conditions（2.89%）.