Preparation And Process Strengthening Of Polyphthalocyanine Gas Diffusion Electrode

Due to the increasing global environmental problems caused by the burning of fossil fuels,fuel cells have attracted much attention in recent years because of their clean environment and high energy density.In fuel cells,a large number of Pt-based electrocatalysts are needed to accelerate the slow kinetics of oxygen reduction reaction（ORR）on the cathode of membrane electrode.However,the high cost and scarcity of Pt catalysts cause people’s attention to shift to non-precious metal catalysts.Metal phthalocyanine has the active site of M-N_x,good catalytic activity of ORR and low cost,which make it have great development potential in oxygen reduction electrocatalysis.In view of the problems of phthalocyanine compounds in the field of oxygen reduction,such as insufficient utilization of active sites,poor conductivity and poor adaptability in practical applications,this paper carried out research on the mass transfer enhancement of phthalocyanine-based gas diffusion electrode.Firstly,the molecular structure of cobalt phthalocyanine（Co PPc）was designed,and the oxygen-containing functional groups（carboxyl groups）on the edge of the phthalocyanine molecules were removed by means of simple chemical reduction.The hydrophilic and hydrophobic modification of Co PPc was carried out to improve the microchemical environment around the metal-nitrogen-carbon active site and reduce the adsorption capacity of water around the active site.Reduced cobalt phthalocyanine（r-Co PPc）and Co PPc showed little difference in ORR performance in the rotating disk electrode test.However,r-Co PPc showed better performance in backpassed oxygen electrolytic cell half-cell,Zn-air battery and alkaline exchange membrane fuel cell（AEMFC）:The ORR performance of the backpass oxygen electrolyzer is obviously better than Co PPc.The peak power density of the Zn-air battery is156 m W cm^-2(at 0.231 A cm^-2),which is 28%higher than that of the Co PPc.The performance of the alkaline membrane fuel cell reaches 450 m W cm^-2(at1.04 A cm^-2),which is improved by 123%,showing better device adaptability.Then biochar was introduced as the carbon carrier of Co PPc.Through chemical activation,the pore structure of corn stalk（CS）was regulated,and the stalk carbon with different pore structure distribution was obtained.The effects of specific surface area,hydrophobicity and conductivity changes on the performance of catalyst caused by different activation degrees and activation-carbonization temperatures were comprehensively considered.when in 900℃,activator proportion and CS quality ratio of 5:1,the stalk charcoal as carrier of Co PPc（Co PPc/CS）has the better performance:it has the best ORR performance in backpass oxygen electrolytic cell.The peak power density of Zn-air battery reached 147.6 m W cm^-2(at 0.237 A cm^-2)and the peak power density of AEMFC reached 296 m W cm^-2(at 0.759 A cm^-2).Compared with unactivated sample,performance improved by 49%and 64%,respectively.In the electrochemical performance characterization of phthalocyanine catalysts,multi-scale electrochemical analysis techniques（RDE,half cell,single cell）were used to explore the key factors affecting the performance of phthalocyanine-based gas diffusion electrode,and in-depth understanding of the relationship between catalytic activity and mass transfer performance.It is proved that fuel cell system is highly sensitive to the change of hydrophilicity of catalys,indicating that the hydrophilicity of catalyst is as important as the catalytic activity,which jointly determines the adaptability of catalyst in it.