Preparation And Performance Study Of Porous Carbon Based Zn-air Battery Electrode Materials

Nowadays,in the context of the energy crisis and environmental problems in human society and the continuous iteration of new generation energy storage and conversion devices,zinc-air batteries based on porous carbon-based transition metal catalyst materials have received extensive attention and the strong support from the society which is in line with my country’s requirements for the development of green and clean new energy.Its main advantages are the wide range of raw materials,low cost,high energy density,and good stability.The reaction kinetics of the zinc-air battery mainly depend on the oxygen reduction（ORR）reaction and the oxygen evolution reaction（OER）,which play a vital role in the electrocatalytic performance of the air cathode.However,the low electrocatalytic reaction activity of ORR and OER has always been the main bottleneck for its development,hindering the commercialization of zinc-air batteries.Its catalytic reaction mechanism is more complicated,and it is affected by the type of catalyst,surface structure,and the interaction between the catalyst particle clusters.For a long time,researchers in related fields have constructed highly efficient multifunctional catalysts by carefully designing the structure of the catalyst and improving the interaction between the carrier and the active site,which have achieved good results in zinc-air batteries.Based on this,this paper explores and improves the heteroatom-doped porous carbon-based transition metal composite material as a multifunctional catalyst for using in zinc-air batteries and the main research content and structure are as follows:（1）First,we synthesized 3D ZIFs with suitable size using dimethylimidazole as the metal organic ligand and Zn²⁺and Co²⁺as the transition metal source.Using the 3D ZIFs prepared above and adding iron salt,cobalt salt,and polyacrylonitrile（PAN）to prepare a uniform electrospinning precursor solution,the electrospinning process is performed by adjusting the appropriate electrospinning parameters to obtain a uniform diameter composite nanofiber membrane with appropriate pore size.Finally,the carbonization pyrolysis process carried out at the appropriate temperature obtained a N-doped/porous carbon nanocomposite material,the surface of which contains a large number of metal nanoparticles of two different sizes:the smaller nanoparticles contain metal-N active sites are rich in ORR active;larger nanoparticles contain high-valence metal active sites with OER activity,and the two types of active sites promote the dual-functional catalytic performance through synergy.Compared with commercial Pt/C or Ir O₂,the half-wave potential during ORR of this N-doped/porous carbon nanocomposite is 0.89 V vs.RHE,and the voltage value at a current density of10 m A cm^-2 is only 1.62 V vs.RHE.When this nanocomposite is used as a battery cathode catalyst to assemble a homemade zinc-air battery,it can cycle 1256 times at a current density of 10 m A cm^-2,and the power density can reach up to 115 m W cm^-2.（2）Here,we designed a N/S co-doped porous carbon-based transition metal composite catalyst through a simple method.The main experimental ideas are:ZIF-8with uniform shape and size were synthesized by a simple one-step hydrothermal method.In a certain solvent,ZIF-8 was used as a template material to uniformly adsorb Co²⁺and Fe³⁺in the solution to form a Zn FeCo-ZIF material.Subsequent pyrolysis process at an appropriate temperature formed a large number of uniformly dispersed Fe-N,Co-N,and FeCo alloy active sites,and the vulcanization process with thiourea as a sulfur source further changed the electronic structure of the porous carbon framework material,forming more defects for the adsorption of active sites,and also forming Co_9-xFe_xS₈ in the high temperature process,which plays a key role in improving the multifunctional catalytic activity of this porous carbon-based transition metal composite catalyst.In the electrocatalytic test,the half-wave potential in the ORR process is 0.97 V vs.RHE,and at a current density of 10 m A cm^-2,the voltage value in the OER process is only 1.64 V vs.RHE,in the HER process is only 225 m V vs.RHE.When used as an electrode material in a zinc-air battery,the stable cycle is more than 70 hours at a current density of 10 m A cm^-2,and the power density reaches134 m W cm^-2,which is obviously superior than commercial Pt/C and Ir O₂.