Preparation Of Zinc Bismuth Based Semiconductor Nanocomposites And Their Photoelectrocatalytic Reduction Of CO₂

Since the industrial revolution,the rapid development of human society has led to a significant increase in the rate of global energy consumption.It is expected to grow from 15TW in 2010 to 27TW in 2050.However,our energy demand still depends on limited and non-renewable fossil energy sources,such as coal,natural gas and so on.Over consumption these fossil fuels not only causes serious air pollution and water pollution,but also results to large amount of CO₂ emission,and serious changes in global climate and destructive effects on the environment.Thus,we urgently need to find green and renewable energy sources to replace traditional fossil fuels.It is generally accepted that solar energy is a kind of green and sustainable energy.It provides about 120 million TW of energy to the earth every year.Therefore,the storage and utilization of solar energy become more and more important.The photosynthesis of plants in nature is the best example for us to learn form.Using solar energy to turn CO₂ and H₂O into useful chemicals is truly the best strategy.It can not only alleviate the effect of global warming,but also provide renewable energy.Photoelectrocatalytic CO₂ reduction is an artificial photosynthetic process that canwellsimulatenaturephotosynthesis.Wehavedesignedannew photoelectrocatalytic cell for CO₂ reduction.The ZnO or Bi-based semiconductor materials with certain optical properties and electrochemical properties as the photocathode,and BiVO₄ as the photoanode.The external silicon solar cell constitutes a new type of photoelectrocatalytic cell.Although semiconductor materials have certain photoelectric feature,it still has limitation in CO₂ reduction.In this paper,the ZnO or Bi-based semiconductors were modified by morphological regulation,modification of organic ligands and construction of heterojunction to make it be better catalysts for photoelectrocatalytic CO₂ reduction.?1?ZnO semiconductor is selected due to its low toxicity,high mobility and good catalytic activity.The Ni foam as the susbstrate,Taking electrodeposition method.The morphology of ZnO nanomaterials was controlled,six different ZnO/Ni-X photocathodes were prepared and used in the photoelectrocatalytic reduction of CO₂.The experimental results shown that the ZnO/Ni-30 have the best selectivity?100%?for C2 products due to it 3D nanorod structure.The formation rate of C2 products is 13.75?M h^-11 cm^-2(416.67?mol h^-11 g^-1).As is well known that ZnO has a wide band gap energy of about 3.2eV,its absorption range is limited to 390nm.It can only absorb ultraviolet light form solar spectra,In order to expand the absorption range,we modified the semiconductor material with anime ligands,prepared four different electrodes material and used them in the photoelectrocatalytic reduction of CO₂.Our experimental results demonstrate that modification of anime ligands can not only increase the absorption of visible light,but also facilitate the adsorption of CO₂,improving the catalytic property.When the A-ZnO/Ni-30 electrode was utilized in photoelectrocatalytic system,that can produce acetic acid and ethanol9.16?M h^-11 cm^-2(277.78?mol h^-11 g^-1),methanol 23.3?M h^-11 cm^-2(707.07?mol h^-1g^-1).?2?Bismuth oxyhalide have good response to visible light because of suitable band gap.In recent years,it has been widely used in the field of photocatalysis.BiOCl with good 2D layered structure was selected.BiOCl was in-situ grown on FTO by solvent-thermal synthesis.However,the forbidden band width of BiOCl is about3.19-3.34eV,which can only absorb part of ultraviolet light,and photogenic electron holes are easy to recombination.In order to solve these two issues,the heterojunctions of Bi₂WO₆/BiOCl were fabricated.They were characterized by SEM,TEM,XRD,XPS,¹H-NMR and applied to photoelectrocatalytic CO₂ reduction.The heterojunction is more favorable for the separation of photogenic electron and holes,The total yield of carbon based products was significantly higher than that of the precursor BiOCl.The selectivity of C2 products in BCW-6 heterojunction was up to 80%,and the total yield of carbon based products(25.72?M h^-11 cm^-2)was 3 times that of BiOCl(8.57?M h^-11 cm^-2).