The Study On Preparation Of Copper-based Self-supported Gas Diffusion Electrode And Electrocatalytic Carbon Dioxide Reduction

With the increasing use of fossil fuels worldwide,carbon dioxide（CO₂）has been emitted in large quantities since the industrial revolution,resulting in a series of environmental problems.Therefore,there is an urgent need to develop green ways to convert CO₂and finally realize carbon cycle.By utilizing green and renewable electricity such as hydropower and wind power to electrocatalytic CO₂reduction reactioncould convert CO₂into fuels and value-added chemicals,which provides a promising way to reduce atmospheric CO₂concentration in an environmentally friendly manner.Among various metals,copper-based catalyst has attracted many attentions due to its unique properties in electrocatalytic CO₂reduction to hydrocarbons.However,copper-based catalyst exhibited low product selectivity and the stability of traditional copper electrode system is poor.It is urgent to develop new catalysts and improve the performance of reaction system to solve the above problems.In this thesis,the self-supported cuprous oxide（Cu₂O）gas diffusion electrode was prepared on commercial carbon paper by electrochemical deposition,and the modification of the electrode was studied.We foucused on Au-Cu₂O self-supported gas diffusion electrode,which was fabricated via the spontaneous replacement reaction driven by the potential difference between Au Cl₃^-/Au and Cu₂O/Cu²⁺.The corresponding Au-Cu-Cu₂O was obtained by further electrochemical reduction.The aim is to achieve highly selective reduction of CO₂into different products through simple regulation.The main research contents are as follows:1.The Cu₂O was deposited on the hydrophilic carbon paper with double gas diffusion layers by electrochemical deposition method.The prepared electrodes were characterized and utilized for electrocatalytic CO₂reduction and the influence of different deposition time on the product selectivity was investigated.The results show that the main product is H₂when the deposition time is 25 min.The Faraday efficiency of C₂H₄,CO and HCOOH achieves 16%,18%and 15%at-0.6 V（vs.RHE）potential,respectively,when the deposition time extends to 75min.The total current density is 17.79 m A/cm².On the above basis,Au-Cu₂O catalyst was prepared by using the difference of reduction potentials of Cu₂O/Cu²⁺and Au Cl₄^-/Au through spontaneous replacement reaction of 3Cu₂O+6H⁺+2Au³⁺→2Au+6Cu²⁺+3H₂O.Au-Cu-Cu₂O was finally formed by in-situ electroreduction of Au-Cu₂O.The catalyst was characterized by scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,X-ray diffraction（XRD）and electrochemical impedance（EIS）and etc.The corresponding electrocatalytic CO₂reduction activity was tested.Au-Cu-Cu₂O gas diffusion electrode shows higher catalytic activity than Cu₂O gas diffusion electrode.We successfully changed the selectivity of the products by adjusting the deposition time of Cu₂O and the concentration of chlorauric acid solution.When the electrodeposition time was 75min and the concentration of chlorauric acid was 0.01 M,the Faraday efficiency of HCOOH reached 45.4%at-0.6 V（vs.RHE）with an overall current density of 23.5 m A/cm².When the concentration of chlorauric acid was 0.05 M,the product selectivity changed from HCOOH to CO under the same conditions,and the Faraday efficiency reached 90%,while the selectivity remained unchanged during the6 hours stability test.When the deposition time was adjusted to 100 min and the concentration of chlorauric acid was 0.01 M,the Faraday efficiency of C2 product reached 36.4%with the current density of 47.8 m A/cm².2.In this thesis,we prepared Cu_xO-I powder catalyst and loaded it on carbon paper as a non-self-supporting gas diffusion electrode for electrocatalytic CO₂reduction reaction.The activity test showed that the Faraday efficiency of CO reached38%at-1.0 V（vs.RHE）when the loading amount was 4 mg whereas the main product was H₂for 8 mg and 12 mg.In order to inhibit the generation of H₂by-product,we constructed a hydrophobic layer composed of polytetrafluoroethylene（PTFE）on the self-supported Cu₂O gas diffusion surface by impregnation method and investigated the effect of different mass fractions of PTFE on suppressing H₂evolution.With a loading amount of 15%wt,the catalyst could keep the Faraday efficiency of H₂<20%in a wide potential range of-0.6 V to-0.9 V（vs.RHE）.Ag-Cu₂O gas diffusion electrode was prepared by using the potential difference between Cu₂O/Cu²⁺and Ag⁺/Ag.For CO₂reduction,the Faraday efficiency of CO reaches 40.3%,HCOOH reaches 10.2%with the current density of 38 m A/cm²at-0.9V（vs.RHE）.