Preparation Of Porous Fe(Co)/N-C Catalyst And Its Application In Zinc-air Batteries

Zinc-air battery has been regarded as an important supplement and potential substitute for traditional fossil energy because of its high theoretical energy density,high conversion efficiency and low pollutant emission.However,the kinetic process of oxygen electrode reactions is sluggish,limiting the conversion efficiency of the whole device.Traditionally,platinum（Pt）and other noble metal catalysts are widely used as catalysts.However,the high cost and limited stability restrict their large-scale commercialization.Thus,it is of great significance to develop low cost,highly active and stable non-precious catalysts.Carbon-based non-precious metal catalysts are widely used as oxygen electrode reaction catalysts because of their adjustable composition and promising activity towards oxygen electrode reaction.However,the agglomeration of metal ions and encapsulation of active sites in bulk catalyst restricts the activity of catalysts.Therefore,it is highly significant and challengeable to increasing the density of exposed active sites.In this thesis,two strategies have been designed to regulate the structure of electrocatalysts so as to increase the density of exposed active sites:（1）extraction of Co nanoparticles from porous carbon matrix via catalyzing the growth of carbon nanotubes.Porous carbon has widely been used in preparing composite electrocatalysts due to its three-dimensional porous structure and large numbers of edge sites.However,due to the microporous structure in porous carbon,the active site can be embedded,resulting in insufficient release of its catalytic properties.In this paper,we have constructed nitrogen-doped carbon skeleton using biomass materials such as glucose and urea as precursors.The structure of the porous carbon skeleton was regulated via self-catalyzing growth of NCNTs on porous carbon,extracting the Co nanoparticles from porous carbon and thus increase the density of active sites.Eventally,the prepared catalyst exhibited a half-wave potential of 0.85 V（vs.RHE）,which was 30 m V positive than that of the unmodified catalyst.The Zinc-Air-battery assembled with this catalyst showed a peak power density of 146 m W cm^-2,much higher than 75 m W cm^-2 of commercial platinum/carbon.（2）The construction of layered iron,nitrogen doped carbon composite catalyst.Compared with the three-dimensional（3D）porous catalyst,2D layered composite featured with low atomic coordination number and large surface area,promising for boosting density of exposed active sites.In this section,Fe and N co-doped lamellar composite（Fe-NC）have been successfully synthesized via using graphitic phase carbon nitride as template.After optimizing the dosage of precursor and the process parameters,the resultant catalyst exhibit a half-wave potential of 0.86V（vs.RHE）towards ORR,which is superior to thatof commercial Pt/C.The specific capacity of the Zinc-Air-battery assembled with the catalyst as an air electrode is as high as 790m Ah g_Zn^-1,which is better than the specific capacity of Pt/C(732 m Ah g_Zn^-1)under the same conditions.