Effect Of Modified Foam Electrode On Cathodic Reduction Of CO₂

It is inevitable that the fossil fuels are over-used to lead to an energy crisis and the climate crisis.It could mitigate the energy and climate crises and achieve sustainable development by using clean electricity to reduce CO₂to fuel or other small molecule chemicals.It is more important for CO₂utilization and transformation by comparing to carbon capture.It has the advantages of more efficient,safer,lower cost and higher economic benefit for CO₂electrochemical reduction by comparing to other carbon utilization methods.Many metals and alloys could reduce CO₂,but most metal electrodes were plate.In this thesis,metal foams with a higher specific surface area were selected as the working electrode.Three kinds of electrodes,Cu O-Ni-f electrode,acid-modified Ni-Mo-f electrode and Cu₂O-Cu-f electrodes,were prepared on the basis of Ni foam,Cu foam and Ni-Mo foam.The crystal plane structure,surface morphology and elemental composition of above electrodes surfaces were characterized by XRD,SEM and EDS.The prepared electrode was used as the working electrode,the Pt sheet was used as the auxiliary electrode,and the saturated calomel electrode was used as the reference electrode,the electrolysis experiments were carried out in Na HCO₃solution.The effects of modification conditions and electrolysis conditions on the reduction of CO₂were explored.The producing products in electrolyte were analyzed by gas chromatography and liquid chromatography and the Faraday efficiencies（FE）of the product were calculated.The detailed research work were as follows:（1）CuO-Ni-f electrode.The CuO-Ni-f electrode was prepared by modifying Ni foam with basic copper carbonate through a hydrothermal synthesis method.The modified Cu O-Ni-f electrode had spherical Cu O particles on its surface,which covered the entire surface of the electrode.Characterization of the Cu O-Ni-f electrode after CO₂reduction showed a decrease in the intensity of the Cu O crystal plane and the disappearance of the spherical Cu O particles.The effect of different electrolysis potentials,electrolyte concentrations,and electrolysis durations on the Cu O-Ni-f electrode was investigated,and the results showed that the only product of CO₂reduction on the Cu O-Ni-f electrode was HCOOH.The optimal electrolysis conditions for CO₂reduction were potential of-1.6V_vs.SEC,0.5mol·L^-1Na HCO₃solution,and electrolysis duration of 3h,with an FE_HCOOHof 25.02%.（2）Ni-Mo-f electrode.Ni-Mo foam was used as the substrate,and it was modified with HCl and HNO₃,respectively.The effect of modification conditions on electrochemical reduction of CO₂was investigated.It was found that the Ni content on the surface of the Ni-Mo-f electrode modified with HNO₃and the Ni-Mo-f electrode modified with HCl decreased,while the Mo content increased,and spherical particles were generated on the surface.Electrolysis experiments showed that CH₃OH and C₂H₅OH were produced when the unmodified Ni-Mo-f electrode,HCl-modified Ni-Mo-f electrode,and HNO₃-modified Ni-Mo-f electrode were used for CO₂reduction.The unmodified Ni-Mo-f electrode had the highestFECH₃OHand FEC₂H₅OHfor CO₂conversion to CH₃OH and C₂H₅OH,respectively,at potential of-1.4V_vs.SEC,0.5mol·L^-1Na HCO₃solution,and electrolysis duration of 3h,withFECH₃OHand FEC₂H₅OHvalues of 29.13%and 18.64%,respectively.The experiments on Ni-Mo-f modification showed that the optimal conditions were 40℃and a 5vol%HNO₃solution.The optimal electrolysis conditions for CO₂reduction on the HNO₃-modified Ni-Mo-f electrode were potential of-1.4V_vs.SEC,0.5mol·L^-1Na HCO₃solution,and electrolysis duration of 1h,withFE_CH3OHandFE_C2H5OHfor CO₂conversion to CH₃OH and C₂H₅OH of 36.73%and 34.02%,respectively.（3）Cu₂O-Cu-f electrode.Cu foam was used as the substrate and treated at high temperature before being reduced to Cu₂O on the surface using glucose to prepare the Cu₂O-Cu-f electrode.Characterization showed that the Cu₂O-Cu-f electrode had only Cu₂O on its surface,which was distributed uniformly in the form of spherical particles.After electrochemical reduction,the intensity of the Cu₂O crystal plane decreased,and the Cu₂O particles became smaller.The effect of different electrolysis potentials,electrolyte concentrations,and electrolysis durations on electrochemical reduction of CO₂on the Cu₂O-Cu-f electrode was investigated,and the results showed that the products of CO₂reduction on the Cu₂O-Cu-f electrode were CH₃OH,C₂H₅OH,and HCOOH.The optimal electrolysis conditions for CO₂reduction were potential of-1.6V_vs.SEC,0.5mol·L^-1Na HCO₃solution,and electrolysis duration of 3h,withFECH₃OH,FEC₂H₅OH,and FE_HCOOHfor the production of CH₃OH,C₂H₅OH,and HCOOH of 32.45%,55.08%,and 9.48%,respectively.