Study Of Self-supporting Electrode For CO₂ Electroreduction And MEA Configuration

As the industrial revolution progresses,CO₂ emissions increase year by year,leading to the ever-increasing greenhouse effect.Electrocatalytic reduction of CO₂ has the characteristics of mild conditions and controllable reaction rate.It is considered to be a very advantageous method of CO₂ conversion,and the development of CO₂ RR catalysts is the focus of research.However,there are still three problems to be solved about CO₂RR:?1?Low efficiency: CO₂ has low solubility in aqueous solution,and the mass transfer speed is slow;?2?The reaction mechanism is unclear: there are various opinions on the speed control steps;After prolonged electrolysis at a density,the activity is greatly attenuated.This paper will conduct research on these three issues:First,aiming at the "dual function" mechanism of Ni-SACs by Ni site reduction and carbon-nitrogen anchor hydrolysis.Based on the experimental results of CO₂ RR steady-state polarization,the dynamic analysis of CO₂ RR and the sensitivity analysis of model parameters were carried out.With the aid of the transient model equation of CO₂ RR,the electrochemical impedance spectrum and total harmonic distortion spectrum that can express the linear and nonlinear frequency response characteristics of CO₂ RR are obtained.The results show that the dissolved concentration of CO₂ has the most significant effect on CO₂ RR activity.Increasing the loading of Ni-SACs and the number of Ni atom anchors will significantly enhance CO₂ RR activity.Secondly,using the "dual function" mechanism as a guide,a combination of electrodeposition and solid-phase thermal diffusion was used to prepare a three-dimensional self-supporting gas diffusion electrode loaded with Ni-SACs using porous carbon fiber paper as a carrier.Reduce the mass transfer limitation of CO₂ by increasing the "three-phase interface",confirming that the deposition conditions and the type of nitrogen source have an important influence on the electrode morphology and the activity and selectivity of CO₂ RR.By changing the deposition time,temperature and current density of the nickel layer on carbon fiber paper,the effect of the deposition process on the particle size of nickel particles and its relationship with the morphology of Ni-SACs were studied.The results show that when the nitrogen source is melamine,the diameter of nickel particles is positively correlated with the diameter of Ni-NCNTs generated and the internal resistance of the system,and negatively correlated with the selectivity of CO.When the nitrogen source is melamine and the potential is-1.25 V?vs.SCE?,the Faraday efficiency of CO can be up to 85%.Furthermore,changing the nitrogen source to urea can further improve the utilization rate of nickel atoms.When deposited at 25 ?,current density of 2 m A·cm-2 for 1000 s and potential-1.3 V?vs.SCE?,the Faraday efficiency of CO can reach 89%.Finally,a membrane electrode configuration reactor capable of converting CO₂ on a large scale is developed.In view of its reversible attenuation in the KHCO3 liquid layer during long-term electrolysis,the porosity and pore size of the support are changed to adjust the electrolyte capacity and gas distribution in the support layer.The 16 h stability test results show that the porosity of the support layer is negatively correlated with the activity,and the pore size is negatively correlated with the activity decay rate.Furthermore,an enhanced mass transfer electrolytic cell is designed,and an electrolyte flow field plate is designed between the membrane and the cathode.The bubbles in the buffer layer can flow out in time with the liquid electrolyte and enhance the mass transfer.This design can ensure that the electrolytic cell is at 16 In the stability test,neither CO₂ RR activity nor CO's Faraday efficiency was significantly attenuated.