Preparation Of Co₃O₄ Micro-nano Array And Electrocatalytic Reduction Of CO₂ To Syngas?CO+H₂?

In 21^stcentury,people are facing two significant problems,energy crisis and environmental contamination.The emission of large amount of CO₂ into the atmosphere in our daily life and industrial production,which will lead to global warming directly.In recent years,the rapid development of electrocatalytic CO₂ reduction?CO₂RR?technology has attracted widespread attention from some scientists both here and abroad.There is a competitive reaction which is hydrogen evolution reaction?HER?,which greatly inhibits the reduction of CO₂ of the cathode.Syngas?a mixture of CO and H₂?is an important industrial raw material for the production of some chemical products?such as CH₃OH,CH₃COOH and CH₃OCH₃,etc.?and synthetic fuels via industrial processing.The ratio of H₂/CO of the syngas is crucial for the synthesis of the type of downstream products.Therefore,controlling the ratio of H₂/CO is the key to synthesize downstream products.Cobalt tetroxide?Co₃O₄?is a widely used and inexpensive semiconductor material in a variety of applications,such as energy storage and conversion,drug release,sensors,and field emission materials,which due to its stable chemical properties.The main research contents of this paper are as follows:?1?The one-dimensional complex Co?C₄H₄O₄??H₂O?₄ was synthesized by normal temperature ultrasonic method.The micro-nano porous Co₃O₄ polyhedral material was obtained by calcination in air,and the Co₃O₄ polyhedral material was modified by two simple methods.The obtained sample materials were characterized by IR,TG,PXRD,SEM,TEM,XPS and Raman,etc.The electrocatalytic properties of the three materials were investigated.It was found that the current density of the modified samples was significantly higher than that of the pure Co₃O₄ polyhedron samples,and the highest Faraday efficiency?FE?of the modified two Co₃O₄ materials was determined.It is 3%higher?R-Co₃O₄?and 0.6%?Co₃O₄-C?than the pure Co₃O₄ material,and all the corresponding H₂ FE is above 78%.?2?A mixed-metal MOF material?[Ag₄Co₂?pyz??PDC?₄][Ag₂Co?pyz?₂??PDC?₂],denoted as Ag/Co-MOF)was synthesized through high temperature hydrothermal method,and Ag-doped Co₃O₄ material was obtained by calcination under air atmosphere.At the same time,pure Co₃O₄materials were synthesized by simple method for comparison.And the prepared materials were characterized by a series of physical characterization methods.The electrochemical tests showed the introduction of Ag element can improve the selectivity of CO.When the voltage was-1.8 V?vs.SCE?,the FE of CO is 55.6%,and the ratio between H₂ and CO is about 4:5.?3?CuO/Co₃O₄ composite micro-nano arrays were directly synthesized on Cu foil by simple means for electrocatalytic CO₂RR,and CuO nanosheet arrays and Co₃O₄ nanowire arrays were prepared as reference.The prepared materials were characterized by a series of physical characterization methods.The results of electrocatalytic experiments show that the CO of CuO/Co₃O₄ has the highest FE?35.4%?at-1.6 V?vs.SCE?,which is 5.2%and 3.9%higher than that of Co₃O₄ and CuO,respectively and the FE of H₂ of CuO/Co₃O₄material is 61.8%.?4?A beaded ZIF-67 nanowire array directly grown on a copper foam substrate was prepared via a low temperature hydrothermal method.The beaded Co₃O₄ nanowire array?denote as Co₃O₄NAs?was obtained by calcination in an air atmosphere and modified by room temperature immersion.Material Au@Co₃O₄?denote as Au@Co₃O₄ NAs?.The prepared materials were characterized by a series of physical characterization methods.The results of electrocatalysis showed that the highest FE of CO reached to 40.5%for the Au@Co₃O₄ NAs electrode at-2.0 V?vs.SCE?,and the corresponding FE for H₂ was 49.9%.The highest FE of CO of Co₃O₄ NAs electrode is only 27.3%.It shows that the introduction of noble metal Au can greatly improve the selectivity to CO and inhibit the production of HER.