Preparation Of Bismuth Doped Hollow Carbon Nanospheres And Their Performance Toward Electrocatalytic Reduction Of CO₂ To Formic Acid

The consumption of fossil fuels and the massive emissions of CO2 worldwide have caused energy crises and climate change issues.It is urgent to develop alternative energy sources and reduce the concentration of CO2 in the atmosphere.Electrochemical reduction of CO2 to generate fuel or small molecule compounds can not only reduce the concentration of CO2 in the atmosphere,but also provide a strategy idea for the development of new energy sources.Electrochemical reduction of CO2 to formic acid can be achieved only through two electron transfers,avoiding the problems of poor selectivity of the single product and difficult separation of mixed products caused by multiple electron transfer processes.The low rate of electroreduction of CO2 to formic acid restricts its practical application.Efficient electrocatalytic materials are the key to further improving the rate of electroreduction of CO2 to formic acid.In this study,we prepared a series of bismuth doped hollow carbon nanospheres as catalytic materials,and regulated their electrochemical reduction performance for CO2 to formic acid by changing the doping morphology and doping size of bismuth metal.The research results obtained are as follows:Bismuth oxide-supported hollow carbon nanospheres(Bi2O3-C)catalytic materials were prepared by template method.The hollow carbon nanospheres’cavities can be used as nanoreactors to improve the CO2 adsorption activation rate through nanolimiting action,and CO2 adsorption activation sites can be constructed by Bi2O3 loading to accelerate the CO2 reduction rate and improve the rate of CO2 reduction to formic acid.The results show that the performance of electrochemically reducing CO2 to produce formic acid first increases and then decreases with the increase of the doping amount of bismuth precursor.When the doping amount is 2.0 mmol,the Bi2O3 hollow nanospheres catalytic material obtained has the highest selectivity for CO2 reduction to produce formic acid.In an H-type reactor,under the conditions of-1.1 V vs.RHE voltage and 0.1 M KHCO3 electrolyte,the formation rate of formic acid from the electroreduction of Bi2O3-C can reach 1108.11 μmol/L/h/cm2.Bismuth single-atom doped hollow carbon nanospheres(Bix-NC)were designed and prepared as catalytic materials.Bismuth monoatomic were doped into hollow carbon nanospheres,and the unsaturated coordination structure of metal single atom was utilized to further improve their adsorption and activation performance for CO2.Through spherical aberration electron microscopy and Xray absorption spectroscopy,it was proved that metal bismuth was distributed as a single atom in the hollow carbon sphere.The fitting results of X-ray absorption spectroscopy showed that bismuth atoms coordinated with nitrogen atoms.In a gas diffusion electrode reactor,with a current density of 20 mA/cm2,a 1.0 M KOH electrolyte,and an electrolyte flow rate of 45 mL/h,the electroreduction rate of Bi0.15-NC catalytic material to formic acid reached 16.23 mmol/L/h/cm2,which is 14.65 times higher than that of Bi2O3-C nanohollow ball catalytic material.At the same time,the Faraday efficiency of formic acid production(FEHCOO-)can also reach 100%.In summary,by changing the amount,morphology,and size of bismuth doping,the performance of hollow carbon nanospheres towards electrocatalytic reduction of CO2 to formic acid is tuned by changing the amount,morphology,and size of bismuth doping.The optimized Bi2O3-C and Bi0.15-NC exhibit good catalytic activity and formic acid selectivity during the electrocatalytic reduction of CO2.The method and principle for regulating the electrocatalytic activity by doping of this study will provide new ideas for the design and development of highly active and selective catalytic materials for CO2 electroreduction.