Research On Pyrite/carbon Composites As Efficient ORR/OER Catalyst

In order to achieve the goals of carbon peaking and carbon neutrality,it is necessary to develop devices that can effectively convert/store clean energy.This is not only a necessary condition for promoting high-quality development,but also an important direction for our future development.Rechargeable batteries can efficiently realize the reversible conversion of electric energy to chemical energy,such as metalair batteries,fuel cells and lithium-ion batteries.Due to their high theoretical energy density,environmental friendliness,safety and reliability,and low production cost,RZAB(Rechargeable Zinc Air Battery)technology has become one of the most promising energy storage technologies today,far exceeding fuel cells.Although the theoretical energy density of RZAB can reach 1350 Wh kg-1,the actual energy density is only 40-50%of the theoretical level.This is mainly due to the kinetic characteristics of oxygen evolution reaction(OER)and oxygen reduction reaction in the cathode.Therefore,effective measures must be taken to improve the operating efficiency of RZAB.In order to ensure the effectiveness and stability of RZAB,a highly active bifunctional catalyst is needed to simultaneously drive efficient ORR and OER.This study successfully synthesized two electrocatalysts(CoS2 YSS@NC and NC-CoS2/FeS2),both of which showed high catalytic activity.Through various physical characterization methods,such as material composition,elemental valence state,specific surface area,pore size,and apparent morphology,both electrocatalysts were analyzed in depth.Furthermore,electrochemical performance tests were conducted to investigate ORR and OER performance,allowing for the inference of the catalytic mechanism of the catalysts.Both electrocatalysts have good stability and are expected to be widely used in relevant fields.Here,cobalt-doped iron sulfide(CoS2 YSS)nanospheres with a yolk-shell structure were prepared as a template,modified with amino groups as nucleation sites,and coupled with highly conductive needle-like nitrogen-doped carbon through a simple solvothermal method(CoS2 YSS@NC).The labeled CoS2 YSS@NC-0.5 shows gaps between the yolk and shell,and an outer layer of clearly grafted NC,providing a complete structure,an internal position,and three exposed surfaces on the CoS2.CoS2 YSS@NC-0.5 exhibits a high half-wave potential of 0.88 V in ORR activity,significantly superior to commercial Pt/C,and has good methanol tolerance.Due to the formation of highly active CoOOH in situ,CoS2 YSS@NC-0.5 exhibits lower overpotential(244 mV at 10 mA cm-2)and Tafel slope(135 mV dec-1)than RuO2.The CoS2 YSS@NC-0.5 air cathode ZBA battery exhibits good open circuit voltage(1.44 V),specific capacity(772.5 mAh g-1),and cycling stability.Coating the needle-like NC layer on the yolk-shell structure of CoS2 can significantly reduce the charge transfer resistance and achieve excellent ORR/OER activity.The results demonstrate that the integration of highly conductive carbon with sulfide minerals of the pyrite type is an effective strategy to obtain durable bifunctional ORR/OER catalysts.In addition,this study synthesized a new type of bimetallic pyrite and carbon nanocomposite(NC-CoS2/FeS2)through a simple strategy of surface adsorption of Co2+and 2-methylimidazole self-assembly-low temperature sulfidation on PVPfunctionalized MIL-88B.The NC-CoS2/FeS2 morphology shows a hexagonal prism structure self-generated from MIL-88B nucleation particles,and the ΔE(Ej10(1.54 V,OER)-E1/2(0.89 V,ORR))value of NC-CoS2/FeS2 is as low as 0.65,superior to commercial Pt/C and RuO2.This is due to its stable self-assembly structure enhancing mass transfer,The bimetallic sulfides demonstrate remarkable ORR/OER activity and stability,owing to their ability to expose numerous active sites on both inner and outer surfaces,as well as benefit from the synergistic effect between the metals.This paper highlights the role of carbon materials in oxygen electrocatalysis on pyrite/carbon composite materials and studies the positive effect of strong interaction between bimetallic interfaces on the ORR/OER activity of pyrite/carbon composite materials.Through experiments,it is shown that the catalytic active site can form a strong synergistic effect with nitrogen-doped carbon,regulating the charge transfer mechanism and reducing polarization.At the same time,the presence of bimetallic interfaces greatly enhances the catalytic activity of the catalyst.This paper provides a new method for creating efficient and stable bifunctional electrocatalysts based on pyrite.