Performance Optimization And Control Of Photoelectrochemical Cells Based On Bismuth Vanadate Photoanode

Photoelectrochemical cells is an important device which can convert solar energy into hydrogen energy.At present,the conversion rate and stability of photochemical cells are limited by the photoanode,which has not reached the requirement of commercial application.Therefore,the development of photoanode with high performance and good stability is the key to realize the large-scale application of photoelectric chemical cells.Bismuth vanadate,as an n-type semiconductor,has good chemical stability,environmental inertness,and low cost,so it is suitable for photoanode in photoelectrochemical cells.However,bismuth vanadate is easily affected by the rapid recombination of photoelectron-hole and the slow surface oxygen evolution rate,and its actual performance is much lower than the theoretical maximum.In view of this,based on the bismuth vanadate nanoarray,this thesis constructed an efficient and stable bismuth vanadate composite photoanode by controlling the preparation process,parameters and surface interface regulation,so as to optimize the performance of photoelectrochemical cells.Through the study and analysis of the photoanode’s optical and electrical characteristics,the separation of photogenerated charge interface,the law of charge transfer and the mechanism of the photoanode’s surface oxygen evolution reaction were clarified.It provides experimental and theoretical basis for the development of photoelectrochemical cells based on new photoanode.The main contents and innovations of this thesis are as follows:（1）The bismuth vanadate nanoarrays were prepared on transparent conductive glass by electrodeposition.By controlling deposition voltage and total deposition charge,the size and thickness of bismuth vanadate layer were optimized to prepare high performance bismuth vanadate photoanode.Then,a bismuth vanadate/metal phthalocyanine composite photoanode was constructed by adjusting the addition amount of metal phthalocyanine and loading on the bismuth vanadate photoanode.The effects of the arrangement and stacking structure of each component on the oxygen evolution process were analyzed,and the mechanism of photogenerated charge migration and capture was determined.Based on this,the photoanode was optimized and regulated,and finally the efficient and stable bismuth vanadate/metal phthalocyanine composite photoanode was obtained.At 1.23V_RHE,compared with the unmodified bismuth vanadate photoanode,the photocurrent density of bismuth vanadate/cobalt phthalocyanine composite photoanode increased by about 1.4 times to 3.23 m A cm^-2.The maximum photoconversion efficiency of bismuth vanadate/cobalt phthalocyanine composite photoanode was 1.09%,3.6 times that of bismuth vanadate photoanode.（2）On the basis of optimizing the surface structure of bismuth vanadate nanoarray to achieve efficient light absorption,nickel phosphide was modified onto bismuth vanadate photoanode by convenient drop casting method to construct bismuth vanadate/nickel phosphide composite photoanode to optimize and control the surface charge separation characteristics and oxygen evolution reaction performance of bismuth vanadate photoanode,so as to play the synergistic effect between each component,improve the stability and activity of photoanode.At 1.23 V_RHE,the photocurrent density of the bismuth vanadate/nickel phosphide photoanode increased to 3.3 m A cm^-2,which was 2.36 times that of the bismuth vanadate photoanode,and the maximum photoconversion efficiency was 0.93%,which was 4.23 times that of bismuth vanadate photoanode.Further analysis shows that nickel phosphide can be used as a hole storage layer to capture and temporarily store the generated holes,thus effectively promoting charge separation on the electrode surface and improving oxygen evolution rate.