Design,Preparation And Application Of Carbon-based Gas Diffusion Electrode

Energy demand and environmental issues are increasingly prominent.Gas diffusion electrodes,as cathodes for oxygen reduction reaction and anodes for hydrogen oxidation reaction,are widely used in various energy conversion devices such as electrochemical synthesis of hydrogen peroxide,hydrometallurgy,and fuel cell to improve energy conversion efficiency and reduce energy consumption.As a porous electrode that reacts at a three-phase interface,changes in the hydrophilicity and hydrophobicity or changes in the pore structure of the gas diffusion electrode can lead to various mutually constraining factors such as liquid wettability,gas diffusion,and electron conduction.Therefore,based on clarifying the constraints between various factors and their effects on electrode performance,it is necessary to change the hydrophilicity and hydrophobicity of the electrode and regulate the pore structure of the electrode through various means.This paper takes finite element simulation as the starting point,and through changing the contact angle and porosity to conduct simulation calculations to clarify the internal relationship of various constraints.On the basis of preparing carbon supported metal phthalocyanine catalysts to ensure the rate of oxygen reduction reaction,the effects of pore changes in the catalytic layer and gas diffusion layer on the electrode and its electrochemical synthesis of hydrogen peroxide performance were studied.On the basis of using commercial platinum carbon catalyst to ensure the rate of hydrogen oxidation reaction,the influence of changes in the hydrophilicity and hydrophobicity of the catalytic layer on the electrode and its hydrometallurgical performance was studied.The main conclusions are as follows:A three-dimensional model was constructed for finite element calculation.The results showed that increasing the contact angle of the catalytic layer would reduce the liquid saturation in the catalytic layer,resulting in a constraint relationship between an exponential increase in gas diffusivity and an exponential decrease in ionic conductivity.An increase in the porosity of the catalytic layer and the gas diffusion layer will form a constraint relationship between an exponential increase in gas diffusivity and an exponential decrease in electronic conductivity.Under these constraints,there are optimal values for electrode performance.The highly stable catalyst for oxygen reduction reaction is a carbon supported metal phthalocyanine prepared by conjugation self-assembly of both metal phthalocyanine and commercial carbon black.By adjusting the type and proportion of the central metal of the metal phthalocyanine,as well as the loading amount,oxygen reduction tests were conducted simultaneously.The results showed that the carbon loaded chromium cobalt bimetallic phthalocyanine with a loading amount of 5% and a ratio of chromium phthalocyanine to cobalt phthalocyanine of 1:2 exhibited excellent two-electron oxygen reduction activity,achieving a hydrogen peroxide yield of 92%,and maintaining performance without degradation after 10000 cycles.The cathode of the oxygen reduction reaction prepared based on this catalyst was subjected to pore structure regulation and used for the electrosynthesis of hydrogen peroxide.Due to the decrease in pressure during electrode hot pressing,there is a constraint relationship where porosity increases but conductivity decreases.Therefore,by adding carbon nanotubes to the catalytic layer and the gas diffusion layer,the electrode porosity and conductivity are simultaneously improved.In the electrochemical synthesis of hydrogen peroxide test,the gas diffusion electrode prepared with a carbon nanotubes content of 5% in the catalytic layer and 6% in the gas diffusion layer exhibit higher hydrogen peroxide production and current efficiency due to its better gas transport ability.Combined with the hydrogen peroxide/ozone oxidation method,the above electrodes achieve 100% removal of various phenols per hour.Hydrogen depolarization anodes based on commercial platinum-carbon catalysts with excellent catalytic activity for hydrogen oxidation reactions were tuned for hydrophilic or hydrophobic states and used for zinc electrowinning.Due to different hydrophobicity,polyvinylidene fluoride bonded and polytetrafluoroethylene bonded hydrogen depolarization anodes have different initial performance and degradation behavior.The polyvinylidene fluoride bonded hydrogen depolarization anode with lower hydrophobicity exhibits better electrocatalytic performance due to better electrolyte wettability,but simultaneously degrades faster.Both hydrogen depolarization anodes exhibit good performance for the zinc electrowinning.The cell voltage is lower than1.5 V,and the energy consumption is lower than 1320 k Wh/t,which is 60% less than the traditional lead silver anode.