Study On The Preparation Of Tantalum Nitride-based Heterojunction Materials And Their Photoelectrocatalytic CO₂ Reduction

Since the increase of human activities and excessive energy consumption,the concentration of CO₂ in the atmosphere has dramatically augmented year by year,and scientists all over the world are looking for appropriate methods to ameliorate the energy crisis and environmental problems.As one of the main contributors causing the greenhouse effect,the carbon dioxide could be converted to carbon-based fuels,which is not only conducive to the emission reduction of CO₂,but also can alleviate the problem of energy crisis.Compared with the traditional catalytic conversion of CO₂,the photoelectrocatalytic CO₂ reduction has been put forward by simulating the photosynthesis of natural plants,which is a green and environment-friendly way of CO₂ conversion.Photoelectrocatalytic reduction of CO₂ is a promising transformation strategy,in which,the preparation of catalysts is the key to catalytic researches.Based on the principle of photoelectrocatalysis,the selection of semiconductor materials with strong light absorption performance is beneficial to enhance the photoelectrocatalytic efficiency.In this study,Ta₃N₅ semiconductor materials with good light absorption performance are selected as the matrix.Due to the disadvantages of low separation efficiency of photogenerated carriers,Ta₃N₅-based semiconductors were modified by constructing heterojunctions and loading cocatalysts in order to improve the performance of photoelectrocatalytic reduction of CO₂.?1?The heterojunction materials,M-TNCN-x,?M=Pd,Pt,Ru;TN=Ta₃N₅,CN=g-C₃N₄?,have been designed and used in the study of photoelectrocatalytic CO₂reduction.The Ta₃N₅ semiconductor was firstly sysnthesized by Ta₂O₅ in the ammonia gas atmosphere,and then the Ta₃N₅/g-C₃N₄ heterojunctions were successfully synthesized,and the metal particles were loaded onto the surface of the heterojunction material by electrochemical deposition.A new photoelectrocatalytic cell M-TNCN-x?SCE?BiVO₄ consists of M-TNCN-x photocathode,BiVO₄ photoanode and saturated calomel reference electrode in KHCO₃ aqueous soultion.We investigated the effects of different electrode materials and different applied voltages for CO₂ reduction under the driving of applied voltage and simulated sunlight irradiation,and explored the reaction mechanism of photoelectrocatalytic reduction CO₂.The results indicated that the formation of heterojunction is beneficial to improve the separation efficiency of carriers,and the deposited metal particles can improve the catalytic performance of semiconductors.The Pd-TNCN-2?SCE?BiVO₄cell displays the highest CO₂ reduction activity under-0.9 V,the yield of formic acid is 38.8?M cm^-2 h^-1,the yield of the total hydrocarbon products can reach to 77.2?M cm^-2 h^-1,which is two times than TNCN-2 electrode and four times than pure Ta₃N₅electrode.The p-n type heterojunction materials Ta₃N₅/Co₃O₄-x have been fabricated and used in the study of photoelectrocatalytic CO₂ reduction.The p-type metal oxide semiconductor Co₃O₄ with high absorption capacity of visible light was coupled with n-type semiconductor Ta₃N₅ in various ratios by hydrothermal method.The microstructure and photoelectrochemical properties of materials were characterized by XRD,SEM,TEM,XPS,LSV,EIS and other test methods.The experimental results showed that the formation of heterojunction not only improves the utilization of visible light,but also promotes the separation of photogenerated electrons and holes,thus improving the ability of catalytic reduction of CO₂.Compared with the pure Ta₃N₅ photocathode,the heterojunctions are conducive to the production of C2+products such as ethanol.The total yield of carbon based products in Ta₃N₅/Co₃O₄-2-1photocathode is the highest,which is two times that of Ta₃N₅ photocathode.The yield of ethanol is 12.64?M cm^-2 h^-1,and the selectivity of C2+products is 63%.